I tracked down a Micron ZIP datasheet plus five Tech Notes for the MT42C4256 (DPDRAM -or- VRAM) . First, there is NO pin-compatible 28 pin ZIP of >256K capacity.

This does NOT garentee that we can pump the XGA up to 2MB, nor does it mean the XGA BIOS supports 2MB (or 4MB). The XGA standard DOES support up to 4MB, but does the software support 2MB / 4MB?

I would be thrilled to have a Model 90 with 2MB on-planar. 1024x768x64k.....


MT42C4256Z-8 Datasheet
http://ps-2.kev009.com/ohlandl/video..._Datasheet.pdf

TN-42-01 - Upgrading from 1 Meg to 2 Meg VRAMs
http://ps-2.kev009.com/ohlandl/video/MT_TN-42-01.pdf

TN-42-02 - Designing with MT42C4256/8128 VRAM
http://ps-2.kev009.com/ohlandl/video/MT_TN-42-02.pdf

TN-42-03 - Regular, Real-Time, Split Read Transfers
http://ps-2.kev009.com/ohlandl/video/MT_TN-42-03.pdf

TN-42-04 - Bank Interleaving w/ Extended Data-Out VRAMs
http://ps-2.kev009.com/ohlandl/video/MT_TN-42-04.pdf

TN-42-05 - Four-Column vs Eight-Column Block Write
http://ps-2.kev009.com/ohlandl/video/MT_TN-42-05.pdf