| PDP-5 | |
| Developer: | Digital Equipment Corporation |
| Family: | Programmed Data Processor |
| Type: | Minicomputer |
| Unitssold: | about 1,000[1] |
| Platform: | DEC 12-bit |
| Weight: | 540lb |
| Predecessor: | LINC |
| Successor: | PDP-8 |
The PDP-5 was Digital Equipment Corporation's first 12-bit computer, introduced in 1963.[2]
An earlier 12-bit computer, named LINC has been described as the first minicomputer[3] and also "the first modern personal computer."[4] It had 2,048 12-bit words, and the first LINC was built in 1962.
DEC's founder, Ken Olsen, had worked with both it and a still earlier computer, the 18-bit 64,000-word TX-0, at MIT's Lincoln Laboratory.
Neither of these machines was mass-produced.
Although the LINC computer was intended primarily for laboratory use, the PDP-5's 12-bit system had a far wider range of use. An example of DEC's "The success of the PDP-5 ... proved that a market for minicomputers did exist"is:
all of which described the same PDP-5 used by the United States Coast Guard.
The architecture of the PDP-5 was specified by Alan Kotok and Gordon Bell; the principal logic designer was the young engineer Edson de Castro[9] [10] who went on later to found Data General.
By contrast with the 4-cabinet PDP-1,[11] the minimum configuration of the PDP-5 was a single 19-inch cabinet with "150 printed circuit board modules holding over 900 transistors."[12] Additional cabinets were required to house many peripheral devices.
The minimum configuration weighed about 540lb.[13]
The machine was offered with from 1,024 to 32,768 12-bit words of core memory. Addressing more than 4,096 words of memory required the addition of a Type 154 Memory Extension Control unit (in modern terms, a memory management unit); this allowed adding additional Type 155 4,096 word core memory modules.[14] [15]
Of the 12 bits in each word, exactly 3 were used for instruction op-codes.[16]
The PDP-5's instruction set was later expanded in its successor, the PDP-8. The biggest change was that, in the PDP-5, the program counter was stored in memory location zero, while on PDP-8 computers, it was a register inside the CPU. Another significant change was that microcoded instructions on the PDP-5 could not combine incrementing and clearing the accumulator, while these could be combined on the PDP-8. This allowed loading of many small constants in a single instruction on the PDP-8. The PDP-5 was one of the first computer series with more than 1,000 built.[17]
DEC provided an editor, an assembler, a FORTRAN II Compiler andDDT (a debugger).
With a base price of $27,000 and designed for those not in need of the 18-bit PDP-4, yet having "applications needing solutions too complicated to be solved efficiently by modules systems" the PDP-5, when introduced in 1963, came at a time when the minicomputer market was gaining a foothold.[18]
