Last Updated: Tuesday, April 05, 2005

Fundamentals. 1

Basic Electronics and Number Systems. 1

Using the Right Tools. 2

Inside the Case. 3

Serial and Parallel Ports. 19

Fundamentals

Basic Electronics and Number Systems

Voltage measures the electrical pressure in a circuit.
Amps measure an electrical current’s strength.
A semiconductor that can store one of two toggled values is a transistor.
A multimeter is a device that can measure more than one property of electricity.
Antistatic bags are treated to become conductive.
Common Electrical Measurements:

Measurement	Description	Application
Amps	Measures a current’s strength or rate of flow	The amount of current needed to operate a device; for example, a hard disk drive needs 2.0 amps to start up, but only .35 amps for typical operation.
Ohms	Measures a conductors resistance to electricity	Resistance of less than 20 ohms means that current can flow through a computer system.
Volts	Measures the electrical pressure in a circuit.	A PC power supply generates 4 levels of voltage: +5 volts (V), -5V, +12V, and -12V.
Watts	Measures the electrical power in a circuit	A PC power supply is rated in a range of 200 to 600 watts.
Continuity	Indicates the existence of a complete circuit.	A pin in a DIN connector registers 5V on a digital voltage meter (DVM or multimeter) when grounded to another pin.

Volts measure pressure and amps measure current. Current isn’t needed to have voltage. When a water faucet is off, water pressure still exists. There is just no current.
The PC uses DC power. The PC’s power supply converts power from the AC wall outlet into DC power for the computer.
The four DC power levels produced by the power supply in a computer are -5V, +5V, -12V, and +12V.
A digital circuit is an electronic circuit that accepts and processes binary data using the rules of Boolean algebra – the logic of AND, OR, NOT, and so on. Digital circuits are made up of one or more electronic components placed in series to work cooperatively to achieve the logical objective of the circuit.
A resistor acts much like a funnel to slow down the flow of current in a circuit.
A capacitor is like a storage bin to hold a charge. The PC has a few large capacitors that can literally kill you if you make contact with them, such as the capacitors in the monitor and in the power supply.
A diode is a one-way valve that allows the current to flow in only one direction.
A transistor is a semiconductor that stores on binary value.
Transistors, resistors, capacitors, and diodes produce logic gates. Logic gates create circuits, and circuits make up electronic systems.
A human feels ESD at around 3,000 volts, but only around 30 volts are needed to damage electronic components. ESD is a far greater threat to the PC than anything else the PC service technician might accidentally do.
The largest number that can be stored in a certain number of bits is calculated by raising two to a power represented by the number of bits minus one.
2F8 is the default address of IRQ3 and COM2.
The radix of a number is the value that 10 represents in that number’s number system. The radix of decimal is 10, the radix of binary is 2, and the radix of hexadecimal is 16.
Any number to the zero power is 1.
Electrical current is measured in Amps. The strength of an electrical current is measured with an ammeter in amps. The forces of electricity inside the computer can be measured, and each type of measurement tells you something different about the computer.
Computer components can be damaged by an ESD charge of 30V. It doesn’t take very much of an ESD charge to zap the internal components of a computer. Most PCs are designed to have some ESD protection as long as their cases are intact and closed properly. Cases are chemically treated or have copper fittings designed to channel electrostatic discharge away from the sensitive components inside. The danger from ESD begins when the case is opened and the fragile components on the motherboard are exposed. When a human with a static electrical charge touches anything inside the case, the charge can travel along the wires interconnecting the various electronic components. One of the wires may lead inside a component, and when the charge nears a metal part with an opposing charge, the effect is that the internal wires and elements of components can explode or weld together. Most of the computer’s electronic components use from 3 to 5 volts of electricity. An ESD shock of 30 volts can destroy a computer circuit. An ESD shock you can feel has around 3,000 volts. An ESD shock you can see carries about 20,000 volts. The real problem with ESD damage is that not all of it is obvious. If an entire component is destroyed, you know it, and you replace the piece. When a component has been damaged but continues to work, though, days, weeks, or even months may pass before the component fails completely. More frustrating is intermittent partial failures that can’t be isolated.

Using the Right Tools

Loop-back plugs are used to diagnose a parallel or serial port on a PC
The range of values used when measuring VDC is 3V to 12V.
Placing one probe on a pin at an end of a serial cable and the other probe on a pin at the other end of the cable checks for continuity.
The abbreviation DVM stands for Digital Voltmeter. Some multimeters don’t measure continuity and so they’re called digital volt meters. A multimeter is a voltmeter, an ammeter, and sometimes a ohmmeter all rolled into one. A multimeter measures electrical resistance, voltage, and current. Most multimeters used by field technicians are battery powered, but some of the higher-end models use AC power from a wall plug. When you set up a multimeter for use, you must set three things:

The type of current you’re measuring: AC or DC (also known as VDC – voltage direct current).
What you’re measuring: You set the appropriate indicator or dial to either voltage (volts), current (amps), or resistance or continuity (ohms).
The range of values expected: If you’re measuring voltage from the power supply, the voltage range is 3V to 12V, and for the AC wall plug’s output, the range is around 105V to 125V. You can find Autorange multimeters that sense the incoming power and set the range automatically.

A multimeter has two probes: a red (positive) probe and a black (negative) probe. When you test a device, place the red probe on the hot point, or high point of the current and place the black probe on the ground, or low point. The voltage of the circuit is calculated as the difference in the readings of these two points.

Inside the Case

The Motherboard

The three standard motherboard types are AT, Baby AT, and ATX.
The four primary types of bus structures found on most motherboards are Address, control, data, and power.
The 486DX was the first to feature a built-in math coprocessor.
The Pentium processor generates about 185 degrees Fahrenheit.
MMX is short for Multimedia extensions.
BIOS is an acronym for Basic Input/Output System.
The BIOS process that verifies the integrity of the hardware is the POST.
Using software to control the upgrading of the BIOS ROM is called Flashing.
You can use a Jumper to reset the CMOS settings, including the startup password.
CMOS settings are changed by running the BIOS setup program.
You will commonly hear the motherboard referred to as the systemboard. In most usage, a systemboard goes beyond a motherboard by integrating video, audio, graphics, and other device support into the board’s architecture. IBM has called its motherboard a systemboard from the beginning. Apple Computer calles theirs a logic board, and still others call it a planar board.
The shape, packaging, and to a certain extent, the function of a motherboard is called its form factor. Three standard forms of motherboards exist:

AT: A motherboard patterned after the original IBM AT motherboard.
Baby AT: A smaller motherboard used in clone machines.
ATX: Smaller like the Baby AT board, but installed with a 90-degree rotation. The ATX motherboard allows for easier installation of full-length expansion cards and cables and is easier to cool.

A microprocessor is an integrated circuit that contains millions of transistors interconnected with very small aluminum wires. Its processing capabilities are used to control and direct the activities of the PC by interacting with the other electronic components on the motherboard. The exact functions performed by a microprocessor are dictated by software.
The 486DX was the first CPU to have a math coprocessor built into it.
Since 1981, microporcessors have been packaged in a form factor (package style) called the Pin Grid Array (PGA), which arranges its transistors into a square shape. The PGA microprocessor installs on the motherboard in a special socket called a ZIF (Zero Insertion Force).
Newer ZIF sockets, such as ZIF Socket 7, also come with a lever (ZIF handle) to lock and release the chip.
Packaging abbreviations:

DIP – Dual Inline Packaging. This is the most common package for all types of integrated circuits. It is usually a black plastic or ceramic body with a row of metal pins along each side.
PGA – Pin Grid Array. There are various sizes of PGA packages and mountings. The 486 uses a 169-pin package; the Pentium processor mounts in either a 273- or 296-pin socket; and the Pentium Pro uses a 387-pin mounting.
SEC – Single Edge Contact – Mounts the processor as a single module into a specially designed slot on the motherboard.

Microprocessor Characteristics

CPU	Package	Speed (MHz)	Data Bus (bits)	Memory (MB)	Co- processor?	Cache (K)
8086	DIP	8	16	1	No	0
80286	PGA	20	16	16	No	0
386DX	PGA	40	32	4096	No	0
386SX	PGA	25	16	16	No	0
486DX	PGA	25, 33, 50	32	4096	Yes	8
486SX	PGA	20, 25, 33	32	4096	No	8
486DX2	PGA	40, 50, 66	32	4096	Yes	8
486DX4	PGA	75, 100	32	4096	Yes	16
Pentium	PGA	100, 133, 150, 166	64	4096	Yes	16
Pentium MMX	PGA	150, 166, 200	64	4096	Yes	32
Pentium Pro	PGA	166, 200	64	4096	Yes	16
Pentium II	SEC	166, 180, 200, 266, 300+	64	4096	Yes	64

The 486DX was the first CPU with an integrated math coprocessor; The Pentium Pro offers a 64-bit data bus; and the Pentium and Pentium II processors offer MMX.
The Pentium processor is basically a combination of two 486DX chips that create a parallel processing environment that Intel calls superscalar.
Intel’s 386 Overdrive and 486 Overdrive processors provide 386 and 486 processor owners with Pentium-level performance without the need to pay for a new Pentium computer. The Overdrive processor increases the speed of the processor about 2.5 times the motherboard’s bus speed.
MMX (multimedia extensions) technology has added three features to the Pentium processor:

Fifty-seven new instructions to improve video, audio and graphics capabilities.
SIMD (Single Instruction Multiple Data) technology, in which one instruction can control several data items.
Cache doubled to 32K.

The Pentium processor operates at 185 degrees Fahrenheit. The cooling system is designed to keep the processor in this range. Therefore, you want to keep the PC’s case closed to ensure that its cooling system is operating efficiently. In fact, the cooling system on a Pentium PC sucks air into the case, whereas earlier systems blew air out of the case.
You can find four primary bus structures on most motherboards:

Address: The components on the motherboard pass memory addresses to one another over the address bus.
Control: Used by the CPU to send out signals to coordinate and manage the activities of the motherboard components.
Data: Because the primary job of the computer is to process data, logically the data must be transferred between peripherals, memory, and the CPU.
Power: The power bus is the river of life for the motherboard’s components, providing each with the electrical power it needs to operate.

The number of wires in a bus controls the number of bits that can be transferred over the bus.
Memory chips come in three package sizes:

Dual inline package (DIP): Small byte-size pieces installed individually.
Single inline memory module (SIMM): Large economy size pieces that combine multiple DIPS on a single module.
Dual inline memory module (DIMM): High capacity modules that have memory on each side of the module board that connects through a single connector.

The BIOS code is installed on the motherboard in a ROM chip.
The jump instruction of the BIOS program is located at address FFF0h of conventional memory.
Flashing is updating the contents of a ROM chip under software control.
Cold Boot Processing:

Step	Activity
Power Initialization	The motherboard chipset holds the CPU at bay until the power supply initializes.
BIOS startup	The processor reads the jump address and starts the BIOS program.
POST (Power-On Self Test)	The BIOS checks the hardware system – any errors are signaled with error beep codes.
Video and peripheral BIOS	The video card and any other device BIOSes execute.
System Check	After displaying its startup screen, BIOS checks memory, storage drives, ports, and other devices – any errors are signaled with error messages on the screen.
Plug-and-Play (PnP) check	If BIOS supports this standard, it detects and configures any Plug-and-Play devices.
Summary screen	The BIOS displays a summary of the PC’s configuration. On some systems, it displays long enough to read.
Boot device	The BIOS determines which drive is the boot drive and looks for the volume boot sector or the master boot record.
Op Sys running	Control passes to the boot sector code and the operating system.

The POST is a hardware diagnostic routine built into the BIOS that checks the PC’s hardware to make sure that everything that’s supposed to be there is, and that everything is working properly. The POST process ensures that the system is ready to begin the boot sequence.
BIOS beep codes can be used to troubleshoot hardware failures occurring in the POST procedure.
POST Hardware Diagnostic Message Groups:

Code	Description
1xx	Systemboard errors
2xx	Main memory errors
3xx	Keyboard errors
5xx	Color Monitor errors
6xx	Floppy disk controller errors
14xx	Printer errors
17xx	Hard disk controller errors
86xx	Mouse error

CMOS Entries and Possible Settings:

Entry	Settings
Parallel port	Unidirectional, bidirectional, ECP, EPP, enabled/disabled
Serial port	COM port assignment, I/O address, IRQ, enabled/disabled
Floppy Drive	Boot sequence level, size, speed, density
Hard drive	Size and standard AT type number (used to indicate volume, cylinders, heads, capacity, and so on
Processor	CPU type and speed
Memory	Size and type
Standard system	Date, time, passwords, values

A three-pin jumper located near the CMOS battery on most motherboards can be used to reset CMOS settings to their default values, including the password.
The primary functions of the ROM BIOS are gathering configuration information and initializing the computer when powered on and providing software to communicate directly with hardware components when the OS is functioning. In addition to handling startup functions for the processor, BIOS is the basic input/output system.
You open the case on a PC that has been making a strange sound and find that the cooling fan has fallen off the CPU. It is possible that the thermal grease was never applied to the top of the processor. Thermal grease acts somewhat like an adhesive as well as a heat transfer material.
Built-in video and drive controllers make a systemboard different from a motherboard. Most new boards should technically be called systemboards for this reason.

Memory Systems

On older PCs, the DIP package form was installed in sockets directly on the motherboard.
The most common type of DRAM used is the EDO technology.
SRAM, much faster and more expensive than DRAM, is used for memory caching.
Nonvolatile memory used to permanently store instructions is ROM.
Individual DRAM chips soldered to a small circuit board are called a SIMM.
Parity involves the use of an additional bit for each 8 bits of data.
EDD or Error Correction Code can detect and correct 1-bit errors in data.
Virtual memory is the combination of physical memory and hard disk space, which gives the appearance of more memory than is actually available.
The first 640K of system memory is called conventional memory.
The upper 384K of the first megabyte of memory is expanded or upper memory area.
All memory above 1MB is called extended memory.
Two basic types of memory are in the PC:

RAM (random access memory): Holds the instructions and data in use by the operating system and software applications before and after they pass to the CPU. RAM is volatile; to hold its contents, it must have a steady power source. Should the power stream be broken, anything stored in RAM is erased.
ROM (read-only memory): Is nonvolatile and retains its contents through even the darkest power outage.

Shadowing is the process of copying the contents of the BIOS ROM into RAM for faster access to the instructions by the CPU.
DRAM must be refreshed every two milliseconds. A special refresh logic circuit reads and then rewrites the contents of each DRAM address, whether it’s in use or not.
DRAM chips come in three package forms: DIP (Dual In-line Package), SOJ (Small Outline J-lead), and TSOP (Thin, small outline package).

DIP DRAM is used to install memory directly on a motherboard.
SOJ and TSOP DRAM gained popularity with the development of the SIMM (single inline memory module). These components mount directly on a circuit board’s surface. These packaging forms make it possible to build memory modules, SIMMs and DIMMs (dual inline memory modules), that may contain many separate DRAM chips.

The characteristics of each of the DRAM technologies:

Extended Data Out (EDO) is the most common type of DRAM, although it is only slightly faster than FPM memory. It’s common in most Pentium and later PCs, except those with memory buses over 75 MHz.
Fast Page Mode (FPM) DRAM is occasionally called non-EDO RAM. It’s generally compatible with all systemboards except those with memory buses with speeds over 66MHz.
Burst Extended Data Out (BEDO) DRAM is EDO memory with pipelining technology added for faster access times. BEDO allows much higher bus speeds than EDO. But, this standard has little chipset support.
Synchronous DRAM (SDRAM), like its SRAM cousins, is tied to the system clock and reads or writes memory in burst mode.
Video RAM (VRAM) is a specialized DRAM physically separated from main memory. VRAM applies dual porting, which allows the processor and the video card’s refresh circuitry to access the memory at the same time.

The SRAM that is included along with the cache controller is internal, or level 1 (L1), cache. Additional external SRAM is called external or level 2 (L2) cache.
Characteristics of DRAM and SRAM:

DRAM	SRAM
Slow and must be constantly refreshed	Fast and doesn’t require refreshing
Simple	Complex
Inexpensive	Expensive
Physically small	Physically large

Officially, ROM is the nonvolatile memory used to permanently store instructions and data that can’t be altered in normal operations.
Types of ROM chips:

PROM (Programmable Read-only Memory): Stores data or instructions as firmware and can’t be reprogrammed.
EPROM (Erasable Programmable Read-Only Memory): Can be erased by exposure to ultraviolet light through a little window on the chip’s top and can be reprogrammed with a chip burner.
EEPROM (Electrically Erasable Programmable Read-Only Memory): Can be flash programmed with software; also called flash ROM.

The first code that the CPU has access to is on the ROM.
SIMMs must be installed in pairs. Each bank of memory for a SIMM has two sockets. You must fill the bank before moving on to another bank.
When a character fails to have the appropriate number of bits, it causes a parity error. A parity error can be the first signal of a host of problems.
Parity memory chips contain an extra bit used to check the integrity of the data stored in each byte and nonparity memory does not.
Virtual memory is the combination of installed physical memory and hard drive space that gives the appearance of more memory than is actually installed on the system.
Virtual memory is the basis for multitasking in Windows 95.
Memory on the PC is broken into four basic divisions:

Memory	Description
Conventional Memory	The first 640K of system memory. Used by standard DOS programs, device drivers, TSRs, and anything that runs on standard DOS
Upper Memory Area	The upper 384K of the first megabyte of memory, located right above conventional memory. Reserved for system devices and special uses such as BIOS ROM shadowing. Also called expanded memory or reserved memory.
High Memory Area	The first 64K (less 16 bytes) of the second megabyte of memory. Although it’s the first 64K of extended memory, it can be accessed in real mode. Used by DOS to preserve conventional memory.
Extended Memory	Technically, this is all memory above 1MB, but in actuality it is memory above the high memory area. Used for programs and data in protected mode, such as under Windows.

EMM386.EXE frees up conventional memory by allowing unused portions of the reserved memory area to be used for DOS drivers and memory-resident programs.
The best way to implement EMM386 is by adding the following lines to the CONFIG.SYS file in the DOS root directory:
DEVICE=C:\DOS\EMM386.EXE
DOS=UMB
If you don’t want to run EMS emulation, but you do want the ability to load drivers and TSRs to upper memory, the NOEMS option is added
DEVICE=C:\DOS\EMM386.EXE NOEMS
DOS=UMB
High memory area is the first 64K of the extended memory area. It’s also the only part of extended memory that a program in real mode can access. This space is normally used by DOS after the following specification is included in the CONFIG.SYS file:
DOS=HIGH
Expanded memory expands base memory to its full 1MB. Extended memory extends memory on up to the clouds.
The most commonly used DOS extender is HIMEM.SYS. With HIMEM.SYS, DOS is magically extended to see extended memory.
To add expanded memory emulation, move some of the drivers and TSRs to upper memory, move DOS into the high memory area, open up the extended memory frontier, and include the following code in the CONFIG.SYS file:
DEVICE=HIMEM.SYS
DEVICE=EMM386.EXE
DOS=HIGH.UMB
All versions of Windows 3.x need HIMEM.SYS running to access extended memory.
The LOADHIGH and DEVICEHIGH commands also put upper memory blocks (UMB) to use. The LOADHIGH and LH commands are used on the DOS command line or in the AUTOEXEC.BAT file to start a program and direct the operating system to place it into the upper memory area. For example:
C:\> LOADHIGH C:\PxP\PxP.EXE
loads the driver PxP into the upper memory area. This statement works only if HIMEM.SYS and EMM386.EXE device commands have been included in the CONFIG.SYS file.
DEVICEHIGH is used in the CONFIG.SYS file to assign a device driver to UMB, commonly done with the mouse driver, as shown in this example:
DEVICE=HIMEM.SYS
DEVICE=EMM386.EXE
DOS=HIGH.UMB
DEVICEHIGH=C:\MOUSE\MOUSE.SYS
The DOS command MEM reports the status and usage of all memory, including how UMB has been assigned. Typically, you run MEM with its /C options. This option produces a classified report that lets you know how memory is being utilized.
You may see the “/C” switch listed as “/CLASSIFY”.
MemMaker, available in MS-DOS 6.0 or later, manages UMB and extended memory. It scans the CONFIG.SYS and AUTOEXEC.BAT files and automatically edits or inserts the commands discussed previously as needed. It also decides whether device drivers should be placed high or left in conventionally memory and makes the necessary adjustments.
MemMaker is a memory management utility available in DOS 6.0 and later that is used to automatically optimize memory usage.
In its 386 enhanced mode, Windows 3.x needs HIMEM.SYS to execute from the CONFIG.SYS file before it can load. Enhanced mode also creates a virtual memory environment using swap files.
Windows 3.x uses three core files to manage memory and other system resources:

KRNL386.EXE: The kernel file handles memory management as well as loading and executing Windows applications. Depending on the system, KRNL286.Exe could be used instead.
GDI.EXE: The Graphics Device Interface (GDI) handles graphic display and printing tasks.
USER.EXE: The user interface handles user input, communication ports, and the display and interaction of icons, windows, and dialog boxes.

Windows 3.x arranges portions of its memory in heaps that are allocated to GDI.EXE and USER.EXE to use for recording and tracking every icon, mouse click, windows resizing, and other user interface actions. The total of the heaps allocated to these two functions, along with those allocated to the system and text functions, creates the Windows systems resources.
In Windows 3.x, you can view the amount of system resources available in the Windows Help – About Program Manager option.
Windows 95 has effectively eliminated the need for DEVICE entries in the CONFIG.SYS file with the advent of a group of 32-bit protected-mode device drivers. Windows 95 automatically loads these drivers into extended memory when it loads. These 32-bit drivers are called virtual device drivers (VxD drivers) and have .VXD or .386 file extensions.
Frequent general protection faults could be caused by poor quality memory chips. Faulty memory can cause repeated memory parity errors.
You have installed four 4MB SIMMs on your PC, but when you boot the system, only 12MB are counted up. To determine what may have happened to the other 4MB, replace the SIMMs in pairs to determine which is failing. SIMM assemblies must be installed in pairs, so the troubleshooting procedure is to remove a pair of SIMMs and replace them together or to swap banks and individual SIMM assemblies to eventually isolate the bad assembly.
BIOS programs are most often loaded to Upper Memory. The upper memory area is used to hold BIOS programs and memory-resident drivers.
Windows organizes memory into heaps. Windows organizes memory into heaps that are allocated to support system, user, graphics, and text activities.
Windows NT environments are not bound by the memory limitations of MS-DOS. Windows 95 is. Windows NT addresses all memory as one resource without the logical divisions used in DOS and Windows 3.x and 95.
All memory above 1MB is called extended memory. Memory above 1MB is called extended memory.

Storage Systems

Tape storage is a serial or sequential access media
A hard disk cluster is a collection of sectors.
FM and RLL are the two primary data encoding schemes used to translate date into flux transitions on disk media.
An IDE disk drive should never be low-level formatted.
You can connect two hard drives to a single ATA IDE cable.
You must install terminating resistor pack or terminators at the beginning and end of the SCSI chain.
RAID level 0 provides for disk striping without parity.
The two primary utilities used for maintaining and optimizing hard drives in DOS and Win95 are SCANDISK and DEFRAG.
Under DOS and Windows 3.x, 2GB is the size of the largest hard disk partition that can be created.
You can use a disk compression utility to reduce the space used by files on the disk.
An incremental backup copies all the data modified since the last backup.
IDE, also known as AT Attachment (ATA) interface is a simple interface technology compared to its predecessors. With the interface controller built into the disk drive itself, only a passthrough board is needed to connect the device to the motherboard.
EIDE enlarges the capacity into four multigigabyte drives.
A three-pin jumper can be used to indicate a total of eight values, ranging from 0 to 7.
To operate a PC’s CD-ROM drive in a DOS environment, its device driver must load from the CONFIG.SYS files during the boot process.
When installing an IDE CD-ROM drive to a system that has an IDE hard disk installed, you must configure the CD-ROM as a slave. If no IDE hard disk exists, the CD-ROM can be set to be the master, but some CD-ROMs only run as slaves.
The major improvements to the SCSI-1 interface are:

SCSI-2: Also called SCSI Fast-WIDE, includes 16-bit bus (Wide SCSI) and twice-as-fast transfer rate (Fast SCSI).
SCSI-3 and beyond: Includes Ultra SCSI, Wide Ultra SCSI, SCSI Parallel Interface (SPI), and Ultra2 SCSI, which all feature 16-bit bus and from 40 to 80MBps transfer rate.

All SCSI devices should be powered on before the PC to allow the SCSI host adapter to detect and interrogate each of the devices on the SCSI bus.
A Redundant Array of Independent Disks (RAID) is a category of disk drives that employs two or more drives in combination for fault tolerance (error recovery) and performance.
Data striping is the process where data files are subdivided and written to several disks.
Data mirroring involves writing duplicate data segments or files to more than one disk to guard against losing the data because of a device failure.
Important RAIDs:

RAID 0: Striped disk array without fault tolerance. This level provides for data striping but doesn’t include mirroring or redundancy or any protection against device failure.
RAID 3: Parallel transfer with parity. This level is very much like Level 0, except that it sets aside a dedicated disk for storing parity and error correction code (ECC) data.
RAID 5: Data striping with parity. This level provides data striping at the character level and also implements stripe error correction. The ECC data is recorded on a separate disk for each level of data stripe.

Building blocks of disk media organization:

Tracks: Concentric circular areas of the disk. When data is written to the disk, it begins with the outermost track first.
Sectors: Cross-sectioning divisions of the disk that intersect all the tracks. Sectors provide addressing references.
Cylinders: Unique to hard disk drives, cylinders are a logical grouping of the same track on each disk surface in a disk unit.
Clusters: Groups of sectors used by operating systems to track data on the disk. The size of the disk drive determines the actual number of sectors in a cluster.

Before data can be read from a disk, it must be written to the disk through a process called flux transition, which means that the storage media is altered with an electromagnet to either a positive or negative charge. Two different encoding schemes have been used to convert data into flux transitions:

FM (frequency modulation) and MFM (modified frequency modulation): Some of the first widely used encoding methods. These schemes simply recorded a 1 or a 0 as different polarities on the recording media.
RLL (run length limited): Allows for higher track and data density by spacing one-bits farther apart and specially encoding each byte. RLL introduced data compression techniques and most current disk drives use a form of RLL encoding.

Interleave relates to PC hard disks and interlace relates to PC monitors.
The FAT is always located at Track 0 because different disks have different sizes, number of tracks, and so on.
Low-level formatting accomplishes two major things:

Builds the File Allocation Table (FAT) file and records the location of all tracks and sectors on the device.
Physically scans the disk media for defects and records the location of any unusable areas found.

File Systems of old OS’s:

Operating Systems	File System
DOS	File Allocation Table (FAT)
Windows 3.x	Virtual File Allocation Table (VFAT)
Windows 95	VFAT and FAT32
Windows NT Workstation	Windows NT File System (NTFS)

In DOS, Windows 3.x, and early releases of Windows 95, a hard disk over 2GB in size must be divided into partitions each smaller than 2GB if you want to use the entire disk. Windows 95 OSR2 and Windows 98, which implement FAT32, can create a primary partition of 8GB.
The Windows 95 version of DriveSpace creates compressed drives of up to 512MB. Large disk drives usually can’t be compressed as a single volume.
You can create four different types of backups:

An archival backup (or full backup) is one that contains every file, program, table, and so on from the hard disk.
An incremental backup contains only the files that have been modified since the last previous backup.
A differential backup copies all the data added or modified since the last full backup.
A copy backup is created by using a copy command to write a duplicate of a file, directory, or disk to another media.

In a situation where a rotated group of tapes is used for daily backups of a server, and intermittent problems start occurring on different days and at different points in the backup process, the problem could be in the age of the tapes.
To be sure you have the floppy cable installed correctly, you can use two tricks:

remember “Big Red is Number One”
in most cases, the red edge should point toward the AC power cord.

If you have both an IDE disk drive and a SCSI disk drive on a system, the IDE driver should be the boot drive.
The SCSI host adapter is set to 7; the boot hard disk drive is set to 0.

Bus Structures

The two general types of bus structures on every motherboard are Internal and External.
The system bus provides four different system necessities: Power, Control Signals, Addresses, and Data.
The ISA architecture provides a 16-bit bus.
MCA was the first 32-bit architecture.
Plug-and Play is a configuration standard that allows the BIOS and operating system to automatically configure expansion boards and device adapters.
The Type II PC Card is primarily used to add Modems or NICs to portable computers.
System Resources are the resources used to interface, communicate, and control individual device adapters and controllers.
A DMA (direct memory access) channel allows a device to bypass the processor to access memory directly.
An interrupt is a signal from a device to the processor that a service or special action is needed.
The default IRQ for COM1 is IRQ 4.
The default I/O address for LPT1 is 3F8h.
Two general types of bus structures are on every motherboard:

Internal bus: Interconnects main memory, the CPU, and all other components on the motherboard.
External (expansion) bus: Connects the outside world of peripherals to the motherboard.

The internal bus provides the internal components of the computer with four different necessities:

Power: Power comes to the motherboard straight from the power supply. The motherboard uses the system bus to distribute power to its ICs and other components.
Control signals: The control unit within the CPU sends out control signals to coordinate the activities of the system. These signals are carried on a part of the internal bus called the control bus.
Addresses: PC components pass data and instructions between one another using memory location addresses to reference the location of the data or instructions in memory. These addresses are transmitted on a part of the internal bus called the address bus.
Data: The actual data or instructions being transferred between components are transmitted around the system on the part of the internal bus called the data bus.

External (expansion) bus channels:

Clock signal: This connection provides the card with the signal of the bus clock so that it can synchronize its communications with the buses of the motherboard.
Interrupt request (IRQ): A request telling the CPU to interrupt what it’s doing and take care of the special needs of the device sending the IRQ. So that the CPU knows which device is the rude one, devices are assigned IRQ numbers. When you install a new device, it is assigned an IRQ number, which enables the CPU to know which device to service. On occasion, devices may share an IRQ, provided both devices do not attempt to interact with the CPU at the same time.
Direct Memory Access (DMA): DMA channels allow certain devices to bypass the processor and access main memory directly. Some architectures allow more DMA channels than others, but a DMA channel can’t be shared by two devices.
Input/Output (I/O) address: Assigned to each device via the device’s expansion slot. The I/O address also called and I/O or hardware port, allows the CPU to send commands directly to the device. The I/O address is a one-way-only line that works like a reverse IRQ. The CPU uses the I/O address to send a command to the device. If the device responds, it uses the data bus or DMA channel to do so. Only one device can be assigned to an I/O address.
Bus mastering: Another feature attached to expansion slots and expansion cards that allows one device to interact directly with another. Usually, the expansion card plugged into a slot has a bus master processor on the card that directs this activity.

Windows 95 fully supports Plug-and-Play, although Windows NT only partially supports it. Plug-and-Play is compatible with ISA, EISA, MCA, PC Card (PCMCIA), and PCI devices and adapters. All PCI devices are Plug-and-Play, but not all Plug-and-Play devices are PCI devices.
Expansion slot architectures:

8-bit bus: A single slot that supports eight interrupts and four DMA channels, with all of the preassigned.
Industry Standard Architecture (ISA): 16-bit data bus. 8 IRQs and 8 DMA channels. ISA expansion cards were designated to the appropriate IRQ or DMA numbers through jumpers and DIP switches. The ISA architecture also separated the bus clock from the CPU clock to allow the slower data bus to operate at tis own speeds.
Micro-Channel Architecture (MCA): MCA was the first 32-bit option, and featured bus mastering and a 10MHz bus clock for expansion cards. Configured by software.
Extended ISA (EISA): 32-bit data bus, uses software setup, has more I/O addresses available, and ignores IRQs and DMA channels. EISA uses only an 8MHz bus clock to be backward compatible with ISA boards.
Intelligent Drive Electronics (IDE): Used almost exclusively for disk drives. Allows up to two different devices on each expansion slot. Extended IDE (EIDE) allows up to four drives to be connected to a single slot.
VESA Local Bus (VLB or VL-bus):
Peripheral Component Interconnect (PCI) bus: Introduced with the Pentium PC, PCI is a local bus architecture that supports either a 32- or 64-bit bus, which allows it to be used with both 486 and Pentium computers. The PCI bus is also processor independent because of a special bridging circuit contained on PCI boards. Its bus speed is 33MHz, giving it much higher throughput than earlier cards. The PCI architecture and expansion slot also supports ISA and EISA cards. PCI cards are also Plug-and-Play.
Universal Serial Bus (USB): Allows for the connection of up to 127 external serial devices.

Bus Architecture Characteristics:

Bus	Bus Width (bits)	Bus Speed (MHz)	How Configured
8-bit	8	8	Jumpers and DIP switches
ISA	16	8	Jumpers and DIP switches
MCA	32	10	Software
EISA	32	8	Software
VL-Bus	32	Processor Speed	Jumpers and DIP switches
PCI	32/64	Processor Speed	Plug-and-Play

PCMCIA (Personal Computer Memory Card International Association) is used to add external devices to a notebook or hand-held computer. Three standards exist:

Type I: Cards that are 3.3mm thick, are used for memory additions, and have a single row of connectors.
Type II: Cards that are 5mm thick and used primarily to add modems or NICs. Type II cards have two rows of connectors.
Type III: Cards up to 10.5mm thick, which are often used to add an external hard disk to a notebook computer. Type III cards have four rows of connectors.

System Resources refers to the mechanisms used to interface, communicate, and control individual device adapters and controllers, along with the serial, parallel, and mouse ports.
An interrupt is a signal from one part of the computer (the requesting device) to the processor indicating that a service or special action be taken that only the CPU can perform.
Interrupt requests are sent to a special system component, called and interrupt controller, which either is a separate chip on the motherboard or is incorporated into the chipset. The interrupt controller receives and verifies requests and passes them on to the processor.
An IRQ is assigned to one specific device, and it just doesn’t work to have more than one device assigned to an IRQ at one time. If two devices were assigned to the same interrupt, the processor could become confused and send its response to the wrong device at possibly the wrong time, causing untold horrors to happen. Assigning two devices to the same IRQ creates an IRQ conflict, a serious system no-no.
An IRQ conflict can cause both devices to perform sporadically – in the best case – or not to work at all – in the worst case. Similar devices can share IRQs, but they can’t be used at the same time. IRQs are assigned by the system BIOS during POST and the boot process.
IRQ assignments:

IRQ#	Default Use	Description
0	System Timer	Reserved interrupt for the internal system timer.
1	Keyboard controller	Reserved interrupt for the keyboard controller.
2	Bridge to IRQs 8-15	In cascaded interrupt systems, IRQ 2 is used as a link to IRQs 8 to 15, which means it’s not available for general use; if needed by an older (IBM PC/XT) system, it’s replaced by IRQ 9.
3	COM2 and COM 4	Many modems are preconfigured for COM2 on IRQ 3. It’s also used as the default interrupt for COM4.
4	COM1	Normally used by the serial mouse. It’s also the default interrupt for COM3.
5	Sound Card	Often the default IRQ for network interface cards. Also used by PC/XT systems for the hard disk drive and is the default interrupt for LPT2. Most sound cards are preset to IRQ 5.
6	Floppy disk controller	Reserved for the floppy disk controller.
7	LPT1	Although not reserved for it, this interrupt is normally used for the first parallel port and printer.
8	Real-time clock	Reserved for the real-time clock timer, which is used by software to track events to “real-world” time. (IRQs 8-15 are not available in 8-bit systems.)
9	None	A popular choice for network interface cards, but it’s general available for any use. It does replace IRQ 2 in cascading interrupt systems, so it should not be used if IRQ 2 is in use.
10	None	Generally available and unencumbered because no other devices are vying for it.
11	None	Often used by the SCSI host adapter if present, but normally this line is open and available. Some PCI video cards and IDE sound cards try to use IRQ 11.
12	Motherboard mouse (PS/2) Connector	On motherboards supporting a PS/2 mouse (mini-DIN connection on the motherboard), this IRQ is reserved for the PS/2 mouse. A PS/2 mouse on this interrupt frees up IRQ 4 (and COM1) for other uses. Otherwise, this IRQ is available.
13	Math coprocessor or floating point unit	Reserved for the integrated floating point unit (386DX and later) or a math coprocessor (386SX and earlier).
14	Primary IDE adapter	Reserved for the primary IDE controller, which controls the first two IDE (ATA) disk drives. On PCs with no IDE devices, it can be reassigned in the BIOS setup for other uses.
15	Secondary IDE adapter	Reserved for a secondary IDE controller, if present. Can be reassigned in BIOS.

Every device in the PC uses input/output addresses (called I/O addresses or port addresses). The address in the I/O address points to the location in memory that’s assigned to a specific device to use for exchanging information between itself and the rest of the PC.
Common I/O Address Assignments:

I/O Address Range	Device or Port Commonly Assigned
000-00Fh	DMA channels 0-3 controller
020-021h	IRQ 0-7 interrupt controller
060h, 061h	Keyboard
0F8-0FFh	Math coprocessor
130-14Fh	SCSI host adapter
170-177h	Secondary hard disk controller
1F0-1F7h	Primary hard disk controller
200-207h	Game port
220-22Fh	Sound cards
278-27Fh	LPT2 or LPT3
2E8-2EFh	COM4
2F8-2FFh	COM2
300-30Fh	Network cards
3B0-3BBh	VGA video adapter
378-37Fh	LPT1 or LPT2
3E8-3EFh	COM3
3F0-3F7h	Floppy disk
3F8-3FF	COM1

A direct memory access (DMA) channel allows a device to bypass the processor to directly access memory. Those devices with a DMA channel assignment gain the advantage of faster data transfers that do not have to pass through the CPU.
DMA Channel Assignments

DMA Channel	Assignment
0	DRAM refresh
1	Available
2	Floppy disk controller
3	Available
4	Link to second DMA controller
5	Available
6	Available
7	Available

Logical device names are assigned to serial ports (which are given the logical names COM1 to COM4) and parallel ports (LPT1 and LPT2).
Logical device names are assigned during the POST process by the system BIOS.
Logical Device Name Assignments

Port	I/O Address	Default IRQ
COM1	3F8-3FFh	4
COM2	2F8-2FFh	3
COM3	3E8-3EFh	4
COM4	2E8-2EFh	3
LPT1	378-37Fh	7
LPT2	278-27Fh	5

Type I PCMCIA (PC Card) cards are used to install RAM, Type II cards are used to install a modem or network card, and Type III cards are used to install disk drives.

Power

The PC power supply converts AC power into DC power.
The power supply also contains the main cooling fan of the PC.
The PC power supply generates five voltages: +5V, -5V, +12V, -12V, +3.3V
The PC power supply’s output is measured in watts.
A Power surge happens when disturbances create a temporary high-voltage burst that travels down the power line.
Line noise is small variations in the voltage of the power line.
A surge suppressor reduces power problems by absorbing spikes and smoothing line noise.
UPS stands for Uninterruptable power supply.
A Green Star device reduces its power consumption by 99 percent in sleep mode.
During the POST processing, an error code of 021 indicates a power supply error.
Kinds of problems the PC can experience from external power:

Line Noise: Consists of small variations in the voltage of the power line.
Power surges: A power spike or overvoltage happens when disturbances, such as distant lightning strikes or other anomalies in the electrical supply grid, create a voltage spike that travels down the line and to your wall plugs.
Brownouts: Also known as undervoltage, a brownout is the opposite of a power surge and happens when a sudden dip occurs in the power line voltage.
Blackouts: Occur when the power fails completely.
Lightning strikes: This biggest spike delivers a million volts or more.

The PC power supply only functions when it has demand. It has to know how much power to produce from the switching process used to generate its DC voltages. A power supply without some demand will not function properly and may even damage itself. Never “test” a power supply without connecting it to at least one 12V line.
Two types of damage can be done to the PC by electrical forces: catastrophic and degradation. Catastrophic damage is when the device is destroyed all at once in a single event. Degradation is when a device is damaged over a period of instances and begins to fail or has intermittent problems.
The primary component of a surge suppressor is a Metal Oxide Varistor (MOV). The MOV protects the computer by taking the hit from voltage spikes. The problem with MOV is that one big spike or an accumulation of small surges over time can knock it out. Some surge suppressors have a light to indicate that the MOV is still all right.
Consider two main features when choosing a surge suppressor: clamping voltage and clamping speed. Clamping voltage is the voltage at which the suppressor begins to protect the computer. Clamping speed is the time lapse before the protection begins.
Other things to look for in a surge suppressor:

Energy Absorption: Surge suppressors are rated in Joules, which measure their capability to absorb energy. The higher the rating, the better the protection.
Line Conditioning: The line conditioning capability of a surge suppressor is measured in decibels. The more decibels of noise reduction, the better the line conditioning.
Protection Indicators: You have no way of knowing whether you’re protected if a suppressor has no indicator.
Levels of Protection: Surge suppressors have three levels of protection that indicate the maximum number of watts the suppressor allows to pass through anything plugged into it. The standard ratings are 330 (best), 400 (better), and 500 (good).

The standby and in-line differ in the following ways:

The standby UPS operates normally from its AC side. When the power drops, it switches over to its battery backup side.
The in-line UPS operates normally from its DC or battery backup side. The AC side is only used in the event of a problem with the battery-powered circuits.

UPS units are often confused with a standby power supply (SPS), or battery backup, which only supplies power when none is available and has no power-conditioning abilities.
Never plug a laser printer into a conventional PC UPS.
A caution sticker on an electric or electronic device in a PC alerts you to possible equipment damage. A warning label alerts you to possible bodily injury.
Inside the power supply is a 1000 microfarad capacitor.
The primary power supply components are:

Power cord
Passthrough connectors
Power switch
110/220V Selector switch.

Only with the case closed and intact will the PC cooling system function at its optimum.
The Baby AT cools the system by pulling air out of the case and blowing it out through the fan.
The ATX form of power supply sucks air into the case.
The power supply provides the following voltages to the motherboard and drives:

+5V: The standard voltage of motherboards for all 8086, 286, 386, 486 processors below 100MHz, and peripheral boards.
+12V: Used primarily for disk drive motors and similar devices. Modern motherboards pass this voltage to ISA bus expansion slots.
-5V and -12V: Included in most power supplies for compatibility with older systems. Most modern systems don’t use either of these voltages.
+3.3V: A 486 100MHz or above, and all Pentium, Pentium Pro, and equivalent chips run at 3.3V.

The ATX power supply differs from the Baby AT power supply in three primary ways:

ATX has additional voltage and power lines that are used to signal and control the power supply.
The fan blows into the case instead of our like the Baby At, which helps keep the case clean.
The ATX power supply turns on and off with electronic signaling and not a physical power switch. It can also be switched on and off by software, such as a Windows shutdown.

The Baby AT power supply has two 6-wire connectors, and the ATX has a single 20-wire keyed connector.
The P8 and P9 connectors are oriented correctly if all four of the black wires, or grounds, are together in the middle.
The ATX power supply is always on. Power is supplied to the motherboard even when the system power is off. Always disconnect the power cord from the back of the case before working on one.
The larger drive connector for CD-ROMs and HDDs are called a Molex connector. The small FDD ones are called a Berg connector.
A few symptoms that indicate a power supply problem:

The power light on the front panel is off.
The power supply fan isn’t operating.
The computer sounds either a continuous beep or doesn’t beep at all.
The computer sounds a repeating short beep.
The computer displays either a POST error in the 020-029 series or a parity error.

Capacitors in the PC power supply absorb most power spikes. A capacitor is used to absorb a power spike and can be used to provide power to bring up an undervoltage condition.

Outside the Case

Input Devices

The capacitive keyboard used a capacitive membrane module.
The most commonly used PC keyboard format is the enhanced keyboard.
Two popular types of mouse units are mechanical and optical.
A serial mouse connects to a serial computer port.
A PS/2 mouse connects to a mini-DIN-6 connector.
The bus mouse attaches to its own adapter or expansion card.
The standard IRQ assigned to the mouse is IRQ12.
To remove paper bits and food crumbs from a keyboard, you turn it upside down and shake it.
A swab and mild soap are best for cleaning the ball of a mouse.
A 300-range error code displayed during the boot sequence indicates a keyboard error.
The keyboard formats found on any DOS or Windows PC can be grouped into one of four categories:

XT: 83 keys, 10 function keys, numeric keypad and cursor control keys combined, keyboard processor in keyboard.
AT: 84 keys, with the addition of the SysRq key, a larger Return key, and the keyboard processor on system board.
Enhanced: 101 keys, which includes 12 function keys, cursor and screen control keys, and numeric keypad.
Ergonomic: Enhanced keyboard with built-in wristrest, and arched or bowed keyboard shape; may also separate into segments.

Two types of mechanisms are used in PC keyboards: mechanical and capacitive.
The capacitive keyboard is more reliable, slightly more expensive, and found in name-brand keyboards like IBM, Compaq, DEC, KeyTronic, and so on.
Differences between Mechanical and Capacitive keyboards:

Mechanical	Capacitive
Uses electromechanical keyswitches
A plunger presses two contacts together, creating a signal	A paddle contacts the capacitive membrane, creating a signal
Less expensive to manufacture	Expensive to manufacture
Used in clones and generic brand keyboards	Used in brand-name and high-quality OEM keyboards
Heavier than capacitive keyboards	Lighter and more compact than mechanical keyboards
	More reliable

DIN connectors have a notch or key slot that prevents an incorrect connection.
Two fundamental layers to make it input devices work:

Firmware: Stored on a ROM chip either inside the device or on the interface card installed on the motherboard. The firmware contains hardware and BIOS interface information, such as IRQ, COM port assignments, and boot sequence support data.
Device driver: The software that communicates directly with the device itself and interacts with the operating system during normal operations. Device drivers are started during the system boot sequence from either the CONFIG.SYS in DOS and Windows 3.x or by the Windows 95 device management utilities.

The keyboard is typically assigned IRQ 1 and I/O address 060h.
You can clean a keyboard with the computer turned off using the following steps:

Turn the keyboard upside down and shake out any paper, potato chips, cookie crumbs, paper clips, or the like.
Use an aerosol can of compressed air to dislodge any stubborn bits.
Use an all-purpose cleaner and soft cloth to clean the key tops.
Use a lint-free swab and the cleaner to clean between the keys.

To determine whether a keyboard electrical failure is in the keyboard or on the system board, use the following steps:

Power off the computer.
Unplug the keyboard connector from the motherboard.
Power on the computer.
Use a digital multimeter to check the voltages of the connector pins.

If the failure occurs later in the POST or boot sequence, an error code in the 300 to 399 number range displays, indicating a keyboard error.
You can prevent CTS by keeping your elbows at the same level as the keyboard and keeping your wrists straight and higher than your fingers.
The four mouse types and their connectors are:

Serial: Connects via a 9- or 25-pin serial port usually with a DB-9 or DB-25 connector.
PS/2: Connects with a mini-DIN 6-pin plug to a port usually mounted on the motherboard.
Combination
Bus

DEVICE=C:\MOUSE\MOUSE.SYS is added to the CONFIG.SYS file.
The mouse is typically assigned IRQ 12 and an I/O address of 238h.
The sound card is generally assigned to IRQ 5 and I/O address 220h. A sound card can use up to three DMA channels. Channels 0, 1, and 3 for an 8-bit card, and channels 5, 6, and 7 for a 16-bit card.

Output Devices

The CRT is the primary component of the PC monitor.
A CRT paints its image using pixels, which are tiny clusters of color dots.
The VGA/SVGA standard connector has 15 pins.
A sound card usually supports both the SoundBlaster and the General MIDI standards.
A sound card typically uses IRQ 5.
The monitor’s glass builds up static electricity and holds dust on its surface.
The CRT is considered an environmental hazard because it contains lead.
A Green monitor is one that reduces its power by 99 percent in sleep mode.
A CRT has a large capacitor inside that holds an electrical charge.
You should not wear an ESD grounding strap when working inside a monitor.
A process called degaussing eliminates most of the magnetization inside the CRT.
Monitor related terms:

Refresh rate: represents the time it takes the CRT’s electron beam to paint the screen from top to bottom. Refresh rates are expressed as hertz (Hz), which is one complete screen refresh cycle.
Interlacing: Interlaced monitors draw the screen in two passes, drawing only the even count lines on the first pass and just the odd count lines on the second pass. An interlaced monitor usually has more screen flicker in each pass.

Technologies used to control the illumination of the CRT’s phosphor:

Shadow mask: A metal screen with thousands of very small holes. The mask is placed so that the holes are directly in line with the dots of each pixel. The shadow mask absorbs unwanted electrons and prevents the phosphor material between the pixels from being illuminated, which leaves a black border around each pixel.
Aperture grill: Very thin vertical wires instead of the shadow mask’s little openings. These wires let more electrons through, creating a deeper color display. Horizontal wires hold the vertical wires in place to keep the verticals from vibrating.

The number of displayable pixels on a screen is the resolution. The more pixels available for display, the higher the resolution.
The distance between pixels is the dot pitch. The smaller the dot pitch, the better the picture quality.
Different video adapter cards (old):

Monochrome Display Adapter (MDA): Displays mostly text on a monochrome monitor. Resolution is not an issue.
Color Graphics Adapter (CGA): This digital adapter was the first color adapter. It’s capable of displaying four colors. CGA monitors support 320 x 200 (four colors) or 640 x 200 (two colors).
Enhanced Graphics Adapter (EGA): This digital adapter supports 16 colors at a resolution of 640 x 350.
Video Graphics Array (VGA): Introduced by IBM and soon copied by the Super VGA (SVGA) and Ultra VGA (UVGA) adapters. SVGA and UVGA monitors and cards did not define new graphics standards, but merely added a few features to the IBM VGA standard. The VGA card supports up to 640 x 480 (16 colors) or lower resolutions in 256 colors. The SVGA and UVGA adapters are available with resolution as high as 1,280 x 1,024 and up to 16 million colors.

The video card and monitor must use the same graphics standard to work properly.
An accelerated video card has a video coprocessor that enables it to calculate many of the display calculations previously handled by the CPU.
Accelerated video cards include a video coprocessor that offloads video image production from the CPU.
The memory on a video card is called video memory, or the frame buffer.
Specialized video memory technologies:

Video RAM (VRAM): Dual-ported DRAM that requires far less refreshing than ordinary DRAM and can be written to and read from at the same time.
Windows RAM (WRAM): Also dual-ported, but is accessible in blocks, which results in slightly faster transfers over VRAM.
Synchronous Graphics RAM (SGRAM): Represents improvements in the technology of single-ported DRAM that enables the chips to run as much as four times faster than conventional DRAM memories.

A process called degaussing eliminates most of the magnetization inside the CRT.
SoundBlaster-compatible sound cards are normally configured to support:

DMA Channel 1
IRQ5
I/O address 220

Serial and Parallel Ports

Serial data is transmitted 1 bit at a time.
A serial cable can be up to 50 feet in length.
COM1 is commonly assigned to IRQ 4.
A DTR or Data Terminal Ready signal on pin 4 of a serial connector is used to indicate that the DTE device is ready to communicate.
A null modem cable is used to directly connect two computers via their serial ports.
Serial devices are controlled by a UART or Universal Asynchronous Receiver/Transmitter.
Parallel cables should not be more than 15 feet in length.
The IEEE 1284 standard covers bidirectional communications through a parallel port.
To check for system resource conflicts in the Windows operating system, use the device manager.
Serial port problems are usually caused by system resource conflicts.
Serial ports are always either a 9- or 25-pin male connector. A parallel port is always a female connector.
Serial Port System Resource Assignments.

Logical Device	IRQ	I/O Address
COM1	IRQ 4	3F8h
COM2	IRQ 3	2F8h
COM3	IRQ 4	3E8h
COM4	IRQ 3	2E8h

Serial Key Words

Data bits: Indicates the number of bits used in the character coding scheme, or data word.
Flow control (handshaking): The embodiment of the protocol used to control the dialog of two serial devices. Used to manage the data flow by sending a character or signal to stop it.
Parity: Five choices: Even, odd, space, mark, or none.
RTS/CTS (request-to-send/clear-to-send): Sends signals to stop and start the data flow.
Stop bits: Used in certain serial communications to indicate the beginning and end of data words.
XON/XOFF: One of the two most common forms of flow control, it send control characters to stop the flow of data (XOFF) and restart it again (XON). This is the software method of flow control.

Serial connection pin assignments:

Pin Number	Designation	Activity
1	Carrier Detect (CD)	Indicates a connection is established.
2	Receive Data (RD)	All incoming data is received on this pin.
3	Transmit Data (TD)	All outgoing data is sent on this pin.
4	Data Terminal Ready (DTR)	The host device (such as the PC) is ready to communicate.
5	Signal Ground	Not used on PC systems.
6	Data Set Ready (DSR)	The connected device (such as the modem) is able to communicate.
7	Request to Send (RTS)	Host device wants to communicate.
8	Clear to Send (CTS)	Connected device is ready to communicate.
9	Ring Indicator (RI)	The telephone is ringing.

Handshaking accomplishes the hardware flow control between the PC and the modem, as follows:

The DTE (Data Terminal Equipment), or PC, turns on the DTR (Data Terminal Ready) signal, indicating it’s good to go.
The DCE (Data Communications Equipment) acknowledges this message by turning on the DSR (Data Set Ready).
The DTE turns on its RTS (Request to Send) signal to let the DCE know it is ready to receive the data.
The DCE acknowledges this request with a CTS (Clear To Send).
The data flows one bit at a time until one of the devices needs to stop it. This stopping is indicated by either the RTS or CTS being turned off.

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