Memory-Resident Programs
There are a variety of utilities and supplementary programs that can be loaded 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
file. 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.
Programs that use specialized subroutines called
device drivers
can also cause problems with your computer 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 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
Table 1
to configure the card for one of the available IRQ lines.
Table 1. Default IRQ Line Assignments
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. If you install a
non-Plug and Play or legacy card, you may need to run the ISA Configuration Utility to determine the current IRQ settings and to find an
available IRQ line.
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
IRQ5
Available
IRQ6
Used by the diskette/tape drive controller
IRQ7
Used by the parallel port
IRQ8
Used by the real-time clock (RTC)
IRQ9
Used by the video graphics array (VGA) interface (optional)
IRQ10
Available
IRQ11
Available
IRQ12
Used by the mouse port
