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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0001:  Power Supplies - System Board

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XVIII  Memory Mapping
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XIX  Logical Names

The BIOS assigns Logical Names to the devices using an IRQ and memory address. Now IRQ 3 and I/O address 2F8-2FFh becomes Com 2.

This does not mean that you cannot change the standardized IRQ and I/O address. Be strongly cautioned however against doing this, "just because you can". And whenever you are building or working on a new system, be strongly advised to create a map of the system before you start making any changes.

Remember some programs will not ask the Operating System for details such as IRQ and I/O. Some programs require this information in their own setup. And there are a few older programs, such as games, that require the popular default settings for the ISA Sound Blaster. That is:

IRQ 5, I/O 220h, DMA 1

Table 9 shows the classical assignments of IRQs and I/O addresses in the PC.


Table 9: Typical PC IRQ I/O Address Device Assignments

IRQ

Used By

I/O Address

0

System Clock

40h

1

Keyboard

60h

2

Cascade

 

3

Com 2/4

2F8h / 2E8h

4

Com 1/3

3F8h / 3E8h

5

LPT2 / Sound

278h / 220h

6

Floppy

3F0h

7

LPT1

378h

8

Real Time Clock

70h

9

Open

 

10

Open / NIC

 

11

Open / VGA

A000h

12

PS/2 Mouse

 

13

Math Coprocessor

 

14

Primary IDE

170h

15

Secondary IDE

1F0h

IRQ TIP

Write the chart until you can do so from memory. Before you begin your test, re-create the chart.



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