Like most computer manufacturers, Apple uses different sources for its chips, and this policy, though normally unnoticed, has caused some difficulties in upgrading the video RAM (VRAM) in Macintosh LCs, Quadras, and 4*8 video cards. Apple differentiates between its VRAM SIMMs, so you can make sure you buy the right parts when upgrading. However, if already have an upgrade, you may experience strange problems.

For instance, if you have the wrong VRAM on a 4*8 card, the monitor may come up after a cold boot (turning the power switch on) in black & white mode without the "millions of colors" option available in the Monitors Control Panel. Restarting (a warm boot) will cause that option to appear, but the problem will recur every cold boot.

If you use inappropriate SIMMs in a Macintosh LC, a few pixels along the left edge of the screen may intermittently change color. Similarly, inappropriate SIMMs in a Quadra may cause pixels to drop out on large monitors.

To solve the problem, buy the right VRAM expansion kit from Apple or make sure your dealer replaces a defective VRAM SIMM with a correct one. If you bought your VRAM from a third party vendor, complain to them to get a correct SIMM.

Here are the Apple part numbers for the original VRAM SIMMs:

     Part Number  Description
     M0517LL/A    Mac LC 512K VRAM SIMM
                    Use with Macintosh LC only
     M5953LL/A    Macintosh VRAM Expansion Kit
                    Use with Macintosh Quadra only
     661-0609     VRAM SIMM, 256K
                    Use two SIMMs to upgrade Macintosh Display Card
                    4*8 only

Defective VRAM should be replaced with the following service part numbers:

     Part Number  Description
     661-0609     VRAM SIMM, 256K - use with Macintosh Display Card
                                    4*8 only
     661-0649     VRAM SIMM, 512K - use with the Macintosh LC only
     661-0722     VRAM SIMM, 256K - use with CPUs (Quadras and LC)
                                    only

Information from:
Mark H. Anbinder -- mha@baka.ithaca.ny.us