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One of the first timesharing machines, the $DEC\: PDP-1,$ had a (core) memory of $4K\: 18-bit$ words. It held one process at a time in its memory. When the scheduler decided to run another process, the process in memory was written to a paging drum, with $4K\: 18-bit$ words around the circumference of the drum. The drum could start writing (or reading) at any word, rather than only at word $0.$ Why do you suppose this drum was chosen?
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