PC Setup DIMM Patch: large DIMMs (32 or 64 MB) with the 12" PC Compatibility Card.

Realitystorm · Sep 30, 2025

Working on a post for DOS/PC Compatibility Cards and came across a KB article KB026105: PC Setup DIMM Patch.
It "Corrects the problem of not being able to use large DIMMs (32 or 64 MB) with the 12" PC Compatibility Card"
Not sure if this issue was fixed for later versions of PC Setup or not (after PC SETUP 1.5)
Also not clear if the DIMM.sys file is needed even with a patched version of PC SETUP
It may have been included in the Apple Software Upgrades CD-ROM (July 1997)

There is also TA35935: 12 Inch PC Compat Card: Freezes With 32 MB & 64 MB DIMMs (1997-03-01), which describes the problem but does not mention a DIMM.sys file?

TITLE

PC Setup DIMM Patch

Article ID:
Created:
Modified:

26105
9/11/98
9/11/98

TOPIC

Name: PC Setup DIMM Patch
Version: n/a
Released: August 20, 1996
Description: Corrects the problem of not being able to use large DIMMs (32 or 64 MB) with the 12" PC Compatibility Card.
Instructions for using the patch are below.

This software consists of a self-extracting archive. To use, download, double-click the downloaded file (this decompresses it).

DISCUSSION

This archive contains files that will correct the problem of using large (32 or 64 MB) DIMMs with the 12" PC Compatibility Card. Instructions for using the patch are below. This archive contains two different fixes for the same problem. Either method can be used. IMPORTANT NOTE: Supported DIMMs must be 2K refresh, fast-page mode, and symmetrical. Neither EDO nor asymmetrical DIMMs are supported. The 12" PC Compatibility Card will also support 4K refresh DIMMs, but the 7" PC Compatibility Card will not. Please consult your memory vendor for details regarding their DRAM specifications. This fix can be installed on other PC/DOS Compatibility Cards but it will not do anything differently unless it is used with the 12" PC Compatibility Card.-----PC Setup 1.5 Large DIMM patch This is a patch file that contains an update to the PC Setup BIOS for the 12" PC Compatible card. This patch will only modify PC Setup 1.5. Do not attempt to patch or use anything else! After the patch is installed, select Shutdown from the Special menu. Do not select Restart.-----PC "DIMM.SYS" driver This is the same patch in the form of a DOS driver. To use, copy "DIMM.SYS" to the C: drive and add this line, as the first line, to the CONFIG.SYS file: DEVICE=C:\DIMM.SYSAfter that, restart the PC.

NJRoadfan · Sep 30, 2025

Would be curious if PC Setup 1.6.4 or the 3rd party PC Setup 2.0 fixed this. Assuming Apple stored the PC side BIOS in a resource, it should be easy to compare what was patched.

PC Setup DIMM Patch: large DIMMs (32 or 64 MB) with the 12" PC Compatibility Card.

Realitystorm

NJRoadfan

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