Depending on your definitions, the oldest computer I have is a Mathatronics Mathatron model 4-24, serial number 00133, circa 1964. While this machine only deals with numbers, it has multiple storage registers, is programmable, and can do decision-based branching. It also had Input/Output capability. I also have a Mathatron model 8-48, which dates from 1965 (it has more memory). I've been in touch with one of the designers and the design dates from 1963. Unfortunately, neither of my machines is functional. Read all about it on the Desktop Calculators section of my webiste at http://www.calcmuseum.com The oldest full-blown computer I have is a HP2100S. classiccmp(a)classiccmp.org wrote: I was just curious to know what was the oldest computer any of you own.