A Golden Anniversary for a Golden Computer

Brian L. StuartDrexel University

Origins of the PDP-8

Foxboro Corporation and process control CDC 160 by Seymour Cray influenced MIT LINC by Wes Clark influenced DEC DC-12 marketed as PDP-5

PDP-5

Introduced in 1963 6 μS Memory cycle time 12-bit word

To match analog to digital converters Front end for PDP-4 Up to 32KW of memory Built with DEC System Modules

PDP-5

Flip Chip Modules

Introduced in 1964 Faster than System Modules 2 7/16 in by 5 in Roughly equivalent to later SSI logic ICs

Flip Chip Modules

From PDP-5 to PDP-8

Re-implement PDP-5 architecture: Move program counter to register Use flip chip modules Same I/O devices Faster 1.6 μS memory

The Straight 8

PDP-8/S

Bit serial implementation Less expensive and slower

PDP-8/I

Re-implementation using TTL ICs

PDP-8/L

Low cost packaging of PDP-8/I design

PDP-8/E,F,M

Reimplementation using larger boards Lower cost OMNIBUS

PDP-8/A

Larger OMNIBUS boards Keypad front panel

PDP-8 Register Architecture

Single accumulator Single link bit (carry bit) Program counter MQ register No Stack pointer

PDP-8 Memory Architecture

32KW maximum memory 8-4KW fields 32-128 word pages per field Addressing:

Current page direct Zero page direct Indirect Auto-increment indirect

PDP-8 Instruction Set

8 Major Instructions AND: bitwise and TAD: 2's complement add ISZ: increment and skip if zero DCA: deposit and clear accumulator JMS: jump to subroutine JMP : jump IOT: in-out transfer OPR: operate

PDP-8/M Restoration

PDP-8/M Restoration

PDP-8/M Restoration

PDP-8 Impact

Sub $20K Conventional power Table-top size Multiple languages and peripherals Bus structure

→ All point to early microcomputer designs