Installing New Hardware

Installing New Hardware

Although Plug-and-Play has cut down on the amount of this knowledge you must have, it's still importantnot only what these items are, but how they work and what components they are assigned to.

IRQs DMA's, and I/Os

Interrupt Requests are settings that allow components to talk directly to the CPU. I/O Addresses are memory locations reserved for individual components to store data with other components in the computer. IRQs allow components that need specific tasks performed to signal the processor to tell it that the processes are waiting. I/O addresses simply map out memory locations in RAM that components use to share data. IRQ's can be shared between multiple components as long as both components don't use the IRQ at the same time. I/O Addresses can not be shared, and will normally cause the devices using the I/O Address to fail.

Direct Memory Access channels give components to read and write directly to RAM rather than going through the CPU. Most devices don't need a DMA, but DMA's can not be shared between devices that do. DMA Channels 0 and 4-through-7 are not used in a standard system and are available for other items.

Please look at standard_irq.htm for more information.

Here are the Standard IRQ, DMA, and I/O Address Assignments;

IRQ #	Assignment	I/O Address	DMA Channel
0	System Timer	040-043
1	Keyboard	060-064
2	Bridge To IRQ 9	0A0-0A1
3	COM 2&4	2F8-2FF
4	COM 1&3	3F8-3FF
5	Sound Card	220-22F	1 & 3
6	Floppy Disk	3F0-3F7	2
7	LPT1	378-37F
8	System Clock	070-07F
9	Bridge To IRQ 2	N/A
10	Available	N/A
11	Laptop PC Cards	N/A
12	Bus Mouse	238-23B
13	Math Coprocessor	0F8-0FF
14	Primary IDE Channel	N/A
15	Secondary IDE Channel	N/A

So why is this important to know? Simply put, if you install a new piece of equipment you need to know how it connects to the computer. If an item conflicts, you need to know where that device should be assigned, as well as what assignments are available. To be honest, it's only Legacy systems that you need to worry about this with, as Plug-and-Play handles most of this for you. Be prepared to know it all.

Another system you must be aware of is Bus Mastering. Bus Mastering is the ability of devices to by-pass not only the CPU, but memory as well. Bus Mastering devices have microprocessors imbedded inside, and can work totally independent AND concurrent with the main processor. Bus Mastering devices also can communicate with each other without going through RAM or the CPU. This makes the total system faster by requiring the processor to perform less work.