24k #20 — Ghost machine

The most elusive 24k machine may be one that was never built at all. Some may be vellum tigers — impractical, uneconomical, and possibly impossible. Others are house cats, underpowered machines that require all the maintenance of their larger cousins but offer little of the performance. These may exist on paper for no purpose other than making another system seem a bargain.

That‘s where I’m stuck with the IBM System/360 Model 22. Sure, there’s a wikipedia page for the thing that lists its introduction date in 1971. IBM’s archive says that the machine was available in only two memory configurations — 24k and 32k, with the 24k model available for $246,000. I‘m not sure what the market was like in 1971 for $250k machines that held 24k and that did around ten thousand instructions per second but the 16-bit DEC PDP-11/20, introduced a year earlier, could probably have emulated the 32-bit IBM Model 22 in real time. The PDP system could be purchased outright for a couple months’ rent on the Model 22.

I’ve been searching for evidence of an actual sale of a Model 22 with 24k for a year and I have come up completely empty. I think it may be a figment of IBM’s imagination. Real or not, it’s our 20th installment in the 24 x 24k for 2024 series.