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LGP-30 processor
1956
The LGP-30 processor is a bit-serial, drum-based vacuum-tube CPU: built from about 113 vacuum tubes, it holds all of memory and its working registers on a single magnetic drum and processes each 31-bit word one bit at a time as the drum turns under the heads. Its instruction set is sixteen one-address orders, named by the Flexowriter letters Stan Frankel assigned them, working through an Accumulator, a Counter and an Instruction register. Its slow serial timing made optimum coding — placing each instruction and operand where the drum would next reach it — the central programming craft.