from Wikipedia, the free encyclopedia

The PDP-1 ( P rogrammed D ata P rocessor 1 ) was the first minicomputer and was obtained from DEC (1959 Digital Equipment Corporation develops).



From today's perspective, the term minicomputer seems inappropriate, since the PDP-1 was the size of two refrigerators. In contrast to the much larger IBM machines, this PDP could be started up and controlled by a single person. In addition, it could be used by several people simultaneously. Inquiries made to the PDP were processed and issued immediately - unlike larger computers that ran in batches, where the programs were handed over to the operator as a pile of punched cards and the results were printed out the next day could. The PDP-1 was announced in 1960; the first copy was installed in December 1959.

The PDP-1 was implemented with discrete transistor circuits instead of the electron tubes common at the time . However, integrated circuits have not yet been used.

The developer was the DEC founder Ken Olsen . The direct predecessor was the TX-0 , which was still developed at MIT .

Input devices

PDP-1 control panel

Output devices


The computer is supported by the emulators M.ESS and SIMH . There are also numerous space wars! -Simulations.

The computer was programmed in assembly language or in LISP . In contrast to today's computers, the memory was not addressed in octets , but in 18-bit words . The main memory in the basic version consisted of 4096 of these words, which corresponds to 9216  octets .

There are a few basic commands. Most of the others concern the output devices.

Steve Russell on a PDP-1

Basic commands with the appropriate code

  • ADD Y (40) ADD C (Y) to C (AC)
  • AND Y (02) logical AND C (Y) with C (AC)
  • CAL Y (16) JDA 100
  • DAC Y (24) Deposit C in Y
  • DAP Y (26) Deposit Address part AC in Y
  • DIO Y (32) Deposit C (IO) in Y
  • DIP Y (30) Deposits contents AC in Y
  • DIV Y (56) Divide
  • DZM Y (34) Deposit Zero in Y
  • IDX Y (44) Index (add one)
  • IOR Y (04) Inclusive OR
  • IOT Y (72) In-Output Transfer (many commands, subsequent 2 words required)
  • ISP Y (46) Index and Skip
  • JDA Y (17) equals DAC Y and JSP Y + 1
  • JMP Y (60) next instruction from Y
  • JSP Y (62) jump to Y, save program counter in AC
  • LAC Y (20) load AC with C (Y)
  • LAW N (70) load AC with numer N
  • LAW-N (71) load AC with -N
  • LIO Y (22) load IO with C (Y)
  • MUL Y (54) Multiply
  • OPR (76) Operate (9 commands, e.g. 760000 NOP)
  • SAD Y (50) skip next instruction if C (AC) <> C (Y)
  • SAS Y (52) skip next instruction if C (AC) = C (Y)
  • SFT (66) shift, e.g. B. 661 Rotate AC left, 676 Shift IO right
  • SKP (64) Skip, e.g. B. 640200 Skip on plus AC
  • SUB Y (42) subtract C (Y) from C (AC)
  • XCT Y (10) execute instructions in Y
  • XOR Y (06) exclusive OR C (Y) with C (AC)

Some examples of other important commands

  • RPA (720001) read perforated tape alphanumeric
  • RPB (720002) read perforated tape binary
  • TYO (720003) type Out
  • TYI (720004) type In
  • DPY (720007) display one point (CRT Type 30)
  • PAC (720043) punch a card (previously: LAG load a group)


The predecessor was the TX-0 (1955/1956), the first computer with transistors. Text-based games were already running on it, e.g. B. Tic-Tac-Toe .

The second model of the PDP-1 became famous because it was given as a gift to the Massachusetts Institute of Technology (MIT) Cambridge and the famous game Spacewar! developed by Steve Russell and other students.

PDP-1 monitor with "Three Position Display" program

Successors were:

See also

Web links

Commons : PDP-1  - collection of pictures, videos and audio files