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Memory addin boards.

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First post, by Robin4

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Is there any story about those memory add in boards.

I only know they where used in the 386 area in time and mostly on the slower 386 systems.
They had a special connector on the motherboard.
There where 386 motherboard that didnt had any ram sockets or slots on the motherboard it self. They required these memory add in boards.

What i like to know how compatible they are / where on other motherboard supporting these as well.
Or where these cards specific brand made.. So a biostar memory add in board could only used on biostar motherboard..

Are there URLs or links available to the internet which could me provide more information on these boards.
Everything that can teach me something new whole be awesome.

Is there also anything to find about the connectors they where used on the motherboard and how they actually named.

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~ At least it can do black and white~

Reply 1 of 3, by rasz_pl

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totally incompatible between brands and probably even models of same brand

https://github.com/raszpl/FIC-486-GAC-2-Cache-Module for AT&T Globalyst
https://github.com/raszpl/386RC-16 memory board
https://github.com/raszpl/440BX Reference Design adapted to Kicad
https://github.com/raszpl/Zenith_ZBIOS MFM-300 Monitor

Reply 3 of 3, by MikeSG

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A few months ago, I mapped out every pin of one of the latest Biostar boards to have a Memory Card Bus. A 386DX Biostar MB-1333C/40C-CH board.

Board: https://theretroweb.com/motherboards/s/biostar-mb-1333c-ch

If you were to make your own memory card, I think it's possible to only add the extra RAM slots, and the chipset does the rest. No extra logic. The chipset on this board has 8 RAS. Two are used on the board for normal RAM. Two others connect to the Memory Card Bus via a jumper to select RAS 4/5 and RAS 6/7. The Memory Card Bus contains everything that the RAM on the motherboard has.

So you can make a custom board with 8 RAM slots (2 RAS, 16MB max per) for an extra 32MB total RAM, allowing up to 64MB max on the board...

Windows 98 min RAM requirements are 16MB and the default board spec allows 32MB, so hard to see the benefit of going to all that trouble.

The very latest boards to have a Memory Card Bus though are the easiest to make your own card with.... but also this spec sheet attached is only guaranteed for this exact model.

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