[TUHS] Re: Happy birthday, Unix timestamp!

Andrew Hume: if i recall correctly, V1 of Unix had time measured in milliseconds. were folks that sure that this would change before wrap-around? ==== Not milliseconds (which were infinitesimally small to the computers of 1969!) but clock ticks, 60 per second. Initially such times were stored in a pair of 18-bit PDP-7 words, giving a lifetime of about 36 years, so not so bad. The PDP-11's 16-bit words made that a 32-bit representation, or about two and a quarter years before overflow. Which explains why the time base was updated a few times in early days, then the representation changed to whole seconds, which in 32 bits would last about as long as 36 bits of 60 Hz ticks. The PDP-7 convention is documented only in the source code, so far as I know. The evolution of time on the PDP-11 can be tracked in time(II) in old manuals; the whole-seconds representation first appears in the Fourth Edition. Norman Wilson Toronto ON Not that old a timer, but once looked into old time