File talk:EmulexPersyst 4M ISA.jpeg
Are we sure that's 4MB? There's 9 rows of chips, that's normal, they're seemingly 41256 chips, 256K x 1 bit. 9 rows gives 8 bits + 1 bit for parity, normal for PC RAM in the old days (until somebody realised that, since a RAM error just hangs the machine, what's the point!?). Each column of 9 is therefore 256K x 1 byte. There's 12 columns, 12 X 256K = 3MB! Not 4!
Is it intended to upgrade a computer to 4MB, rather than with 4MB? Assuming you've already upgraded your motherboard RAM to 1MB? Which would be fairly usual for the time.
Or is there another 1MB on the other side of the PCB? I doubt that, since RAM chips back then famously ran hot, sticking them on both sides of a PCB would be asking for trouble. I suppose they might do it double-sided if the board was otherwise too big to stick the desired amount into an ISA card's size.
Thank you for assuaging my curiosity, assuming you do...
[ edit: I found this... http://www.vcfed.org/forum/showthread.php?46409-Emulex-Persyst-4-MiB-ISA-memory-board-in-IBM-AT-5170 which says it IS a 3MB card. Makes sense, saves 36 expensive chips from a 4MB one. ]
