I've seen varying dates for the PDP-11/50 release, ranging from "sometime in 1975" to "June 1976, at the same time as the PDP-11/55." What was the actual date of release?

  • Interestingly, the 1976 04 to 55 processor handbook has the 11/55 but not the 11/50. I don't know if that means the 11/50 came and went before 1976, or that it was not yet available in 1976. Also, the 11/45 is said to be available with bipolar memory.
    – dave
    Commented Feb 4 at 17:34
  • 1
    The 1973 11/45 handbook does not mention 11/50 or 11/55, but does (section 2.5) mention availability of core, MOS, or bipolar memory. I remain confused about what the /50 and /55 actually were (given they have the same CPU and same basic structure as the /45). The original idea seemed to be /45 = KB11-A + core, /50 = KB11-A + MOS, /55 = KB11-D + bipolar. But then the /45 was upgraded to KB11-D with options for MOS or bipolar memory. (Seems typical DEC practice).
    – dave
    Commented Feb 4 at 18:12
  • I checked my paper handbooks (circa 1976-1980) and the 11/45 and 11/55 appear together but nothing mentions the 11/50. I guess it had a short life. This tends to push the answer you're looking for towards 'earlier' rather than 'later' in the possible range.
    – dave
    Commented Feb 4 at 19:20
  • This paper says a US Navy postgrad school acquired a couple of 11/50s in late 1974 and early 1975.
    – dave
    Commented Feb 4 at 20:47

1 Answer 1


A history of DEC for 1974 mentions the release in "July" of the DDS-500 using the 11/50 and other processors — so, possibly July 1974 or earlier. However, DEC's fiscal year 1974 was from July 1973 through June 1974. The sequencing in the chronology suggests the "July" reference could be to July 1973.

In July, the Business Products Group (formerly the Commercial Group) introduced their new DEC Data System 500 series. This series, which replaced the earlier 11/05-based series, utilized the PDP-11/40, 11/45 and 11/50 computers, together with several comprehensive operating systems–Commercial Operating System, Commercial Time Sharing System, and Commercial Data Management System (MUMPS)–to provide considerable flexibility to meet the needs of the commercial user.

Also, for fiscal year 1976 milestones,

50,000th computer system, a PDP-11/50, is delivered.

A maintenance manual for the 11/45 and 11/50 was printed as "2nd Edition" and has a March 1974 date. However, it also notes a revision in the "1st Edition": "4th Printing (Rev) April 1973".

Based on the fiscal year sequencing in the chronology and the revision to the maintenance manual, my best guess is that 11/50s were being built in the second calendar quarter (April - June) of 1973 and being offered, at least, as part of the DDS-500 in July 1973. I was unable to find when the 11/50 was released independently of the DDS-500.

  • Ah, the DDS - running COS and CTS systems. Yet another example of DEC selling the same things under different names :-)
    – dave
    Commented Feb 5 at 1:03
  • I was at first a bit shocked by such an early release date, but from a closer look at various sources it appears that the the /45 (1972) and the /50 both used the same KB-11 CPU, but the /45 used core memory, and a model with MOS semiconductor memory was considered a /50, which makes much earlier release date make more sense. Thanks for your citations!
    – cjs
    Commented Feb 5 at 5:18

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