[PATCH] RAM size range correction

[ecksemmess]

I've just noticed that, with some of the early models, the allowed RAM size range doesn't cover the full gamut of what was available on each model during its lifetime. The cloned XT systems are a bit tricky, but I currently own (or have owned) several of these and can attest from experience that some do have early or budget versions that shipped with 64KB. It seems best to err on the side of unrealistically allowing the 64KB option, rather than unrealistically disallowing it. Other than that, I can say for a fact that the three genuine IBM models' RAM ranges are wrong. I've done my best to correct all of these in this patch for model.c.

[SarahWalker]

Everything I've read about the IBM XT suggests that 128kb was the minimum configuration. Was a 64kb configuration actually sold?

[omarsis81]

From Wikipedia
"IBM sold the first IBM PCs in configurations with 16 or 64 kB of RAM preinstalled using either nine or thirty-six 16-kilobit DRAM chips. (The ninth bit was used for parity checking of memory.) After the IBM XT shipped, the IBM PC motherboard was redesigned with the same RAM configuration as the IBM XT. (64 kB in one bank, expandable to 256kB by populating the other 3 banks.)"

"At introduction, a PC with 64 kB of RAM and a single 5.25-inch floppy drive and monitor sold for US $3,005 (equivalent to $7,835 in 2015), while the cheapest configuration (US $1,565) that had no floppy drives, only 16 kB RAM, and no monitor (again, under the expectation that users would connect their existing TV sets and cassette recorders) proved too unattractive and low-spec, even for its time"

https://en.wikipedia.org/wiki/IBM_Personal_Computer

So... not only was 64 KB the minimum, also 16 KB for what I just noticed!

[omarsis81]

Oh, I just noticed you are talking about the XT, my post was for the first IBM PC
Indeed, the minimum for the XT was 128 KB

[ecksemmess]

There absolutely was a 64KB configuration of the IBM PC/XT, though rare. I had one for years. There are a few sites around the web attesting to this--for example, see http://www.old-computers.com/museum/computer.asp?c=286. I also have a few early 80s computing magazines and newsletters where people talk about using XTs with only 64KB of RAM installed. My understanding is that very few were actually sold that way directly by IBM themselves and I don't believe the 64KB configuration was an official offering of theirs, but it was most definitely a possible configuration.

[SarahWalker]

Most of this is committed to rev 607. I left out the PCJr change, as it currently won't boot with 64kb (emulator issue), and the PC change, as without cassette emulation you can't really do anything useful with less than 64kb...

[ecksemmess]

Fair enough. Thanks!