IBM 650

The first successful IBM mainframe. It was released in 1954. Memory was via magnetic drum, mass storage via tape, and input via punched cards. About 1,800 were in use by the late 1950s. Side note: This was the first computer I had any experience on. Memory was scarce so programmers needed to figure out how many CPU cycles were needed for each instruction and then figure out exactly where to store temporary information on the drum so that the computer had to wait the least amount of time to access it. We had fun by writing do-nothing programs that, when run with an AM radio placed next to the computer, played tunes in the radio frequency static.

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