Looks like S-100 bus to me.

And the other ad says 300mb, not 800mb.

sliderider wrote:

Looks like S-100 bus to me.

I've never head of the S-100 bus before. I assumed it was 8-bit ISA. I should have known better as ISA was introduced in 1981.

EDIT: Looked at the ad more closely. It is indeed a S-100 bus card. And it does indeed appear to be a conventional memory expansion card as far as I can tell. I never knew those existed. I thought you had to solder memory chips onto the motherboard or something. I'm afraid my knowledge of 1970s and, to an extent, 1980s hardware is somewhat lacking, as it was long before my time.

sliderider wrote:

And the other ad says 300mb, not 800mb.

Thanks for pointing that out 😦. I guess I need to proofread more...

Errrrr i read "disk system". which does not sound like "RAM" to me. But still 300 MB for 20K sounds like a bargain? The RAM is just 16K, so no idea about that?

AdamP wrote:

EDIT: Looked at the ad more closely. It is indeed a S-100 bus card. And it does indeed appear to be a conventional memory expansion card as far as I can tell.

S-100 systems had no such thing as "conventional memory" - that term refers to the IBM PC platform (ISA, x86) which was introduced much later. 16 KB RAM was the minimum that the PC ever shipped with, and wasn't a popular option even back then... I think the first expansion cards were 64 KB.

S-100 was an older architecture, based on Intel's 8080. Machines with a total of maybe 4 KB RAM were common around 1977, so a 16 KB expansion card would indeed be a "giant" 😉

I didn't know conventional memory only referred to the main RAM of the 8088 and later PCs. Didn't main RAM not become conventional until it broke 640KB? I thought all RAM below 640KB on all PCs became conventional, lower, or base memory after that.

I suppose the RAM on the S-100 was only ever just called RAM, as they never came close to breaking 640KB?

well the 640KB barrier was itself specific to the IBM PC family design, so it can't be applied to other architectures. I think in this case we shouldn't be using the term "PC" ambiguously - S-100 systems could be called personal computers, but not "PCs" in the sense of "IBM PC compatible or related", much like Apples weren't "PCs" either. 😉 you probably know that already, just clearing up my own usage of the term.

the S-100's memory barrier was actually much lower - the addressable limit of the 8080/Z80 was 64 KB. The standard OS was CP/M, and I think some later versions were able to get around this limit somehow... probably analogous to how EMS accessed >1MB on 8088 PCs (bank switching), but not related to the 640 KB "conventional memory" limitation. And by then the S-100 + CP/M platform was starting to die out in favor of IBM PC + DOS, anyway.