"John B" <dylanb(a)sympatico.ca> wrote: Maybe. More likely there are more digits, like 2116, 2114, 2115, 2100, 21MX, 21xx.... Most of the HP1000 CPUs have 21xx numbers as well. The 1000 line was, originally, a bundle of a 2100-family computer with HP's RTE real-time executive; eventually HP silk-screened "1000" on the front instead of "21MX", but the actual model number of the processor (the tag on the back) was still 21xx. There were also the HP2000 time-shared BASIC systems, built out of one or two 2100-family processors. 2100-family processors also found their way into all sorts of big HP test and measurement systems in the very late 1960s and 1970s. For example (note these URLs are *temporary*): http://www.reanimators.org/tmp/8322.jpg - scan of a photo of an 8580B automatic spectrum analyzer; the box at the top of the left rack is an HP2100A. http://www.reanimators.org/tmp/8324.jpg = scan of a drawing of an 8541A automatic network analyzer; the top of the right rack is what an HP2116 looks like, and underneath that would appear to be a drawer, a filler panel, a paper tape reader, and a paper tape punch. (Trimmed 90-some lines of quoted irrelevant text -- c'mon folks, you can use your editors too....) -Frank McConnell