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> UNIX started as a "microcomputer" OS One very minor nit...the PDP-7 where Unix started out cost US$72k+ in 1969 dollars. Nothing compared to the big iron of

• hga 12y ago
  And as far as capabilities go, the PDP-7 could address 64K of 18 bit words, more than double 1st generation microcomputers (those prior to the IBM PC and Apple Macintosh). Then again, I don't think it's generally known how much (very expensive, hand made) core memory was on that first UNIX(TM) PDP-7. Maybe not that much, it next moved to the first model of the PDP-11, which had a max of 56 KiB memory of 8 bit bytes. Then to an 11/45, which could do 64 KiB of code, 56 KiB of data and 8 KiB of stack.
  • kjs3 12y ago
    The 11/45 has a 16-bit address space optionally expanded to 18-bits with an MMU so could do 256KB of memory. With the MMU, you could take advantage of split instruction and data memory, which gave a pair of 64k address spaces mapped into the 18-bit space. No PDP-11 AFAIK have a separate, dedicated stack space. You're thinking of the 8k dedicated I/O page.
    • hga 12y ago
      Ah, yes, for the 11/45 I was referring to what a single program could do. However, as I recall (from the very early '80s when I was using both a 11/44 and 11/45), the MMU had a 8 KiB page size, so the natural thing to do was to divide the data as described, so a stack overflow would trigger a trap. Although after a bit of time with Google, I note the 11/40 manual says all PDP-11s have a location in which to put a stack boundary, so maybe that was a convention which matched what the MMU could do.