ISA Shared Memory – The Tech ARP BIOS Guide

ISA Shared Memory - The Tech ARP BIOS Guide

ISA Shared Memory

Common Options : 64KB, 32KB, 16KB, Disabled

 

Quick Review

This is an ISA-specific BIOS option. In motherboards that have ISA slots, the BIOS can be set to reserve part of the upper memory area (UMA), which resides between 640 KB and 1 MB, for use by ISA expansion cards. This is particularly important for older operating systems like MS-DOS because it frees up conventional memory (the first 640 KB) for use by the operating system and applications.

If your ISA expansion card requires an upper memory area of 64 KB in size, select the 64KB option. Similarly, if it requires just 32 KB or 16 KB of upper memory, select the 32KB or 16KB options respectively.

If you are not sure how much memory your ISA expansion card requires, select 64KB. It will work with cards that only require 32 KB or 16 KB of upper memory. The rest of the reserved upper memory area will be left unused.

If you do not have any ISA expansion cards installed, leave it at its default setting of Disabled. This frees up the UMA for use by the operating system (or third-party memory managers) to store TSR (Terminate and Stay Resident) programs.

 

Details

This is an ISA-specific BIOS option. In motherboards that have ISA slots, the BIOS can be set to reserve part of the upper memory area (UMA), which resides between 640 KB and 1 MB, for use by ISA expansion cards. This is particularly important for older operating systems like MS-DOS because it frees up conventional memory (the first 640 KB) for use by the operating system and applications.

In truly old motherboards with multiple ISA slots, you will have the option to set both the memory address range and the reserved memory size. You may have to set jumpers on your ISA expansion cards to prevent two or more cards using the same memory address range, but this allows you to reserve segments of the upper memory area for your ISA expansion cards.

PCI-based motherboards have no need for so many ISA slots. Most, if not all, only have a single ISA slot for the rare ISA expansion card that had not yet been “ported” to the PCI bus. Therefore, their BIOS only has a single BIOS option, which allows you to set the size of the UMA to be reserved for the single ISA card. There’s no need to set the memory address range because there is only one ISA slot, so you need not worry about conflicts between multiple ISA cards. All you need to do is set the reserved memory size.

To do so, you will have to find out how much memory your ISA expansion card requires. Check the manual that came with the card. It ranges from 16 KB to 64 KB. Once you know how much upper memory your ISA expansion card requires, use this BIOS setting to reserve the memory segment for your card.

If your ISA expansion card requires an upper memory area of 64 KB in size, select the 64KB option. Similarly, if it requires just 32 KB or 16 KB of upper memory, select the 32KB or 16KB options respectively.

If you are not sure how much memory your ISA expansion card requires, select 64KB. It will work with cards that only require 32 KB or 16 KB of upper memory. The rest of the reserved upper memory area will be left unused.

If you do not have any ISA expansion cards installed, leave it at its default setting of Disabled. This frees up the UMA for use by the operating system (or third-party memory managers) to store TSR (Terminate and Stay Resident) programs.

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