Basic Electronics, Computer Terms, and Binary Number Systems.

In order to understand the fundamentals of computer technology, you must have a basic understanding of electronics itself.  This week's objectives are to teach you to be able to identify terminology and concepts of electricity and electronics, understand the hazards of electrostatic discharge (ESD), and understand and use the binary, decimal, and hexadecimal numbering systems.  Without this basic knowledge, your ability to understand how computers work would be greatly limited.  All computers rely on both basic electronics and the binary and hexadecimal numbering systems, so learning these areas well will increase your ability to understand the inner workings of a computer.

Basic Electronics

The easiest way to understand how electricity works is to relate the entire computer system to the human body.  We will use this relationship throughout our tutorials, as it will help you understand not only how computers work but how the human body is a form of a computer.

Where the human body requires blood to transfer oxygen, electricity is required to flow through a computer to transfer power.  The passing of this electricity opens and closes small gates inside the chips on a computer, which is how it processes information.  There are several forces of electricity that relate to the human blood system as well.  Examine the table below;

There are 5 terms you must know to understand and be able to measure electricity.  Each measurement tells you a separate discrete piece of information about the electricity you are using, and can be measured with a multi-meter.  (We will discuss multi-meters in later weeks, as they are a key component in a computer technician's toolbox)

 One difference between the human blood system and the electricity in a PC is that there isn't always a current flow inside a circuit, but there is a voltage rating.  In a human body, there is always a pulse or blood pressure (We hope), whereas if you turn off the computer, no current (or amperage) is registered.  But if you touch the live circuits with your fingers you complete a circuit and get shocked. 

AC/DC

There are two forms of electrical current that electronics use; Alternating Current (AC) and Direct Current (DC).  AC is the electricity coming into your home from the power lines, whereas DC is the electricity from a battery.  They have one simple difference in how they function; DC always flows in one direction, AC flows in both directions.  Electricity flows from a positively-charged area to a negatively-charged area.  With DC power these two areas remain constant, allowing the flow to go in one consistent direction.  AC power switches it's areas of negative and positive charge 60 times per second, alternating the flow of electricity from one direction to the other 60 times per second, or 60 Hertz.

The low voltage systems inside a computer can not use AC voltage, as the transistors inside can't function with electricity flowing in both directions.  Therefore, the power supply inside your computer must switch the AC power input to a DC power in order for your computer to work.  

The components in your computer run off of 4 main power levels; 5V, -5V, 12V, and -12V. 

Digital Circuits

In order for computers to work, electricity must more then just pass through the computer.  It must be processed in some form.  A digital circuit is an electrical circuit that processes binary functions.  These binary functions are processed using a system known as Boolean algebra, and consist of the cunctions AND, OR, NOT, and more.  When you place several digital circuits in series, you can make them work collectively to achieve the logical objective of the circuit.

In order to create a digital circuit, the electricity passing through must be controlled.  This is done through conductors and insulators.  Conductors (just like they sound) conduct electricity, or let electricity pass through them with a certain degree of freedom.  Insulators block electricity from passing through.  Copper, tin, and gold are the main conductors in a computer, and rubber is the main insulator.  That is why you always see conductors wrapped in insulators.

For a digital circuit to work, there had to be something that could be both a conductor and an insulator created.  These are called semiconductors.  When a semiconductor is zapped with electricity, it toggles between a conductor and an insulator, depending on what it was at the time it was zapped.  Essentially it is a switch on a microscopic level.  Zap it with electricity and it opens.  Zap it again and it closes.

In order for computer systems to work, there have to be four electronic components present to regulate and adapt the electrical power passing through them.  They all serve distinct functions necessary for a digital circuit to work.

• Resistor - Slows down the flow of electricity through a circuit, measured in Ohms.
• Capacitor - Holds a charge until it is triggered to release that charge.
• Diode - Makes all the electricity in the circuit flow in one direction.
• Transistor - A semiconductor.

Resistors, capacitors, diodes, and transistors make up logic gates.  Logic gates make up circuits, and circuits make up electronic systems.

Into Everyone's Life A Little Static Must Fall...

Remember rubbing your feet across the carpet and then touching someone in order to see them scream in horror and the blue light passed from you to them?  Wasn't that fun?  Or when you put on that wool sweater and your hair all stood up on end?  In electronics, this is called Electro-Static Discharge, or ESD

ESD is a catch-all term in electronics.  Basically, any discharge of electricity that is uncontrolled and undesired is an Electro-Static Discharge.  Essentially, ESD is an area of negative charge that pulls the positive charge from an electronic device.  If it ended there it would be simple, but ESD has some nasty side effects.  

First off, ESD can destroy electronic equipment.  Most of the components of a computer system are built to handle a 30 volt change in electrical state.  Human's don't even begin to feel ESD until the 2000 to 3000 volt range.  That means that even though you may not feel it, you could be zapping your computer with an ESD at any time.  To put this in perspective, remember that the components in your computer run on about 3 to 5 volts, and the average ESD you can see is about 20,000 volts.  

Secondly, ESD occurs all the time.  Our bodies tend to generate negative fields of energy very easily.  Therefore, you are a walking ESD.  The biggest threat to your computer is not your computer tech skills; It's your body. 

When an ESD travels through an electronic system, it passes through parts of the computer that contain incredibly small parts, measured in microns.   The energy has one of two effects; either it blows the circuit open so it won't close, or permanently welds the circuit closed.  Either effect is detrimental.  Either effect costs money.

How To Protect Yourself From ESD

This should be "How to protect your computer from ESD", but the most important ways of doing this involve you, not the computer.  Here are a few basic tips;

1. When working on a computer, ALWAYS wear an Electro-Static Discharge grounding strap on your wrist.  This strips are THE #1 piece of equipment a computer tech has in his tool box.  When attached to the chassis of the PC or a grounding mat, your chances of zapping your equipment is incredibly small.
2. Keep the humidity around computer components above 50%.  Dry air is a better conductor for ESD, and allows ESD to be passed more easily.
3. Put a grounding mat under your chair at the desk you work at.  If you don't have a grounding mat, there are sprays that perform the same function.
4. Always store unused components in an anti-static bag.

One thing you MUST be aware of is that when you work inside a computer monitor, you NEVER wear an ESD wrist strap.  There is a very large capacitor in a monitor that stores a huge amount of potential energy.  If you happen to wear an ESD strap while working on a monitor, you invite all the energy inside that capacitor to flow out through your body.  (I've touched a fly-back transformer once...  It wasn't fun)  So never wear your ESD strap when working on a monitor.

Number Systems

As hard as this may seem to believe, it is possible for A to follow 9 instead of 10. It's also possible for 10 to follow 1.  We live in a world based on the decimal number system, but computers live in a world built of two totally different systems; The Hexadecimal system, and the Binary system.  If you've worked on computers before, you've seen the hexadecimal system when you see IRQ and COM port references to hexadecimal addresses.  Understanding how these systems work is imperative to understanding how your computer works.

Binary Systems

Binary number systems are the easiest number systems to understand.  They only have two numbers; 0 and 1.  Either a number is an off (0) or on (1).  Since semi-conductors can only be on or off, this is a perfect number system for a computer to understand.

Converting decimal numbers to binary numbers involves a little more information.  You may have seen a number that looked like 00100110 before, and wondered why there were the two 0's before the 1.  This is a binary number, equivalent to our decimal number 38.   

The conversion method involves knowing how Binary number systems work.  They work from right to left, with the first digit always representing equaling 1.  In an 8 bit system (8 possible positions), that makes 1 equal to 00000001.  The second space from the right is twice the first space.  Therefore 2 is equal to 00000010.  The third space is twice the second, the fourth twice the third, and so on.  We can make any number up to 255 using an 8-bit system simply by adding up the positions of the 1's.  Always remember that the next number in sequence is double the number before.  

Lets take the number 157.  We know that 128 is 2⁷, which corresponds to 10000000 on the binary system. (the 7th power or ⁷ means there are 7 zeros after the number.)  Subtracting 128 from 157, we're left with 29.  16 is 2⁴, which corresponds to 00010000.  We're now left with 13.  2³ is 8, or 00001000.  That leaves 5.  2² is 4, or 00000100. That leaves 1, or 00000001.

So we're left with;
10000000
00010000
00001000
00000100
00000001

10011101, which equals 157 in decimal terms.

The key to this system is to try to find the highest number that's a power of 2 that you can subtract from the root number.  In my example, 128, or 2⁷, was the number.  It's best to find your own method for finding the biggest number you can find, but I use my fingers.  1-2-4-8-16-32-64-128-256-512-1024-2048-4096-8192-16384 until I find a number 1 multiple less then the number I'm subtracting from.  It's not scientific, but it works.

Back to the bit size for a second.  I referred to an 8 bit system earlier  This means there are 8 possible 0 or 1 values, each represented as a power of 2.  Most computer systems use either a 32 or 64 bit addressing system now, which calculate out to numbers of size you'll never have to convert.  But remembering how to convert is vital, as it probably will show up on your test.

*Quick Memory Tip* 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 1.

Hexadecimal Numbers

The word hexadecimal means 10 and 6.  (It kind of means 16, but not in a numerical sense as we know it)  the 10 is represented by standard numbers 0 through 9, and the 6 is represented by the letters A, B, C, D, E, and F.

Hexadecimal numbers are used to store the addresses of IRQ, LPT, and COM ports in a computer.   The decimal number of these addresses as they relate to IRQ's and COMs are irrelevant.  The ability to convert decimal numbers to hexadecimal is more important for determining the size of a memory, storage, or address range.  This helps in determining a memory problem or memory size in some older programs.

The method for converting Hexadecimal to decimal numbers is quite complex.  So I'm going to steal a page from IDG's  to explain it better then I ever could.

The radix of a number is the value that 10 represents in that number's number system.  The radix of of decimal is 10, the radix of binary is 2, and the radix of hexadecimal is 16.

What is the decimal equivalent of the hexadecimal number A012F?  Use the process shown here to convert it.

1. Because each position represents a power of 16, the A in A012F represents the positional value of 16⁴.  The A has the decimal equivalent of 10.  So, this position is worth 10X16⁴, or 655,360

2. The next position of value is a 1 in the position of 16², which is worth 256.

3. The next position has a value of 2 X 16, or 32.

4. The last position has a value of F (15) X 16⁰, or 15.  Any number to the zero power 0 is worth 1, so this is the same as 15 X 1

5. Add up the numbers to come up with a value of  655,663

You probably won't be asked to convert hexadecimal numbers on the test, but it still is good knowledge to know.  It will also help later when you deal with I/O Addressing.  Concentrate more on being able to convert binary to decimal and vice versa, and this part of the test will be a snap.