NaBloPoMo – Digital Equipment Corporation PDP 11/45

Digital Equipment Corporation (DEC) introduced the PDP 11 line of computers in 1970.  DEC had effectively invented the mini computer concept with the PDP-8 introduced in 1965.  This was a low cost alternative to the IBM Big Iron.  The PDP-8 had limitations due to its low cost point, small memory space (4096 12 bit words), one interrupt etc.  Yes I said 12 bit.  It was a 12 bit computer.  Toward the end of the 1960s,  the 16 bit computer was to be the big thing.  And the PDP-11 was DEC's entry.  It had some advantages over the PDP 8,  more memory (16 bit addressing gave 64 KWs of memory,  later models even more), more interrupts etc.  The PDP 11 was very popular and many applications and Operating systems own there existence to the PDP 11.  Obviously,  UNIX  had much of its early development on the PDP 11,  but also MS-DOS and CP/M leaned heavily on some concepts of OS RT 11* for the PDP 11.  The PDP11 system supported both multitasking and multiuser setups.

Here is a PDP11/45 console.  The console gave the traditional blinkenlights display and allowed for bootstrapping and diagnostics.  Yep,  you could toggle a program in via the toggle switches.  Set the address hit load, set the value hit load.  Or was it the other way around?  Anyway,  this was originally from WKU's computer science department.  It was built around 1972.  It is non-functional as most of the computer is long gone.

And many of the earlier computers utilized magnetic core memory and the PDP 111/45 was no different:

* RT-11 had an file system so similar to FAT for MS-DOS,  one could create a disk to work on both.  The only one would be the RX33 for the PDP11 and the 1.2 M 5.25 floppy for the PC.  All the files has to be sequential for the PDP11.  So first start with a blank formatted DOS disk and copy the files to it using a PC.  Next on the PDP11,  create the directory entries for the files.  You had to know how many blocks they occupied.  This would destroy the second copy of the FAT but leave everything else intact.  Now you had a disk that could be read natively by both OSes.  Of course RT-11 came first.  Wonder where Bill Gates got his ideas…….

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4 Responses to NaBloPoMo – Digital Equipment Corporation PDP 11/45

  1. Lurkertype says:

    Mr. LT sez:1. Set address on toggles, press load address2. Enter data, press deposit3. Set next data word, hit deposit next4. Repeat 2 and 3 till done.He was toggling imaginary switches in mid-air as he said this.

  2. Lord Kalvan says:

    I assume Mr. LT has significant DEC experience?

  3. Lurkertype says:

    O yes. Their products still linger about our house, as do many leftovers from various DECUS gatherings.They offered him a job years ago but it was for less money than he was already making, in a higher cost of living area with worse weather. Both facts which they knew at the time of offer. WTF?The one he took instead lasted a number of years longer than DEC did, so it worked out. Plus we got a free plane ticket to the E. Coast out of it that got us to our vacation.

  4. Pingback: Project References – CMST 250

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