IBM Card Programmed Calculator (CPC)

by Edna Carpenter

This view shows a Card Programmed Calculator (CPC) system. It was built by IBM out of business machine parts. The printer is an IBM 418 accounting machine. The machine in the back on the left is an IBM 605 accounting calculating unit. The machine on the right is a card punch IBM 527. All three machines were connected by cables as shown on the right side of the picture. Visible to the left of the printer are four IBM 941 storage units.

The CPC operated at a maximum of 150 cards per minute. Each card contained an operation code plus three possible input numbers (10-digit floating point numbers). The possible operations were a multiply or divide, and an addition. The functions sqrt, exp, log, sin, and cos were possible but required more time than one card cycle. Loops were made by making multiple copies of cards or putting the single card deck through the machine as many times as needed. It did not slow down the machine to print out the answers for each operation. There were five mechanical storage units, each holding 20 words. An answer for an operation could be stored but could not be retrieved again until at least two card times later. However, you could always use the previous answer in the next calculation.

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