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Device Drivers

Programs that use specialized subroutines called

device drivers

can also cause problems with your system. For example, a variation in the way

the data is sent to the monitor may require a special screen driver program that expects a certain kind of video mode or monitor. In such cases,
you may have to develop an alternative method of running that particular program

—

the creation of a boot file made especially for that program, for

example. Call the support service for the software you are using to help you with this problem.

Memory-Resident Programs

Many utilities and supplementary programs load either when the computer boots or from an operating system prompt. These programs are
designed to stay resident in system memory and thus always be available for use. Because they remain in the computer's memory, memory
conflicts and errors can result when other programs require use of all or part of the memory already occupied by these TSR programs.

Typically, your operating system's start-up files (such as

config.sys

and

autoexec.bat

) contain commands to start TSR programs when you boot

your system. If you suspect that one of these TSR programs is causing a memory conflict, remove the commands that start them from the start-up
files. If the problem you were experiencing does not recur, one of the TSR programs probably created the conflict. Add the TSR commands back
into the start-up files one at a time until you identify which TSR program is creating the conflict.

Program Conflicts

Some programs may leave portions of their setup information behind, even though you have exited from them. As a result, other programs cannot
run. Rebooting your system can confirm whether or not these programs are the cause of the problem.

Memory Address Conflicts

Memory address conflicts occur when two or more devices try to access the same address in the upper memory blocks (UMB). For example, if a
network expansion card and an expanded-memory page frame are assigned an overlapping block of addresses, a memory address conflict
arises. As a result, when you try to log in to the network, the operation fails.

To resolve this type of conflict, you can change the address of one of the devices. For example, in the case of the network expansion card and
expanded-memory page frame address conflict, you can move the network card to an address block in the range of CC000h through D0000h. To
reassign the expansion card's address block, refer to the documentation for the card.

Interrupt Assignment Conflicts

Problems can arise if two devices attempt to use the same interrupt request (IRQ) line. To avoid this type of conflict, check the documentation for
the default IRQ-line setting for each installed expansion card. Then consult the following table to configure the card for one of the available IRQ
lines.

Table 5. Default IRQ Line Assignments

BIOS Recovery Utility

NOTE: Table 1 lists default IRQ settings. In systems with Plug and Play capabilities, you can modify the default settings. If you install a
Plug and Play card in a Plug and Play system, the system automatically selects an open IRQ line if any are available.

IRQ Line

Used/Available

IRQ0

Used by the system timer

IRQ1

Used by the keyboard to signal that the output buffer is full

IRQ2

Used by interrupt controller 1 to enable IRQ8 through IRQ15

IRQ3

Used by serial port 2

IRQ4

Used by serial port 1