PDP-9



The PDP-9, the fourth of the five 18-bit minicomputers produced by Digital Equipment Corporation, was introduced in 1966. A total of 445 PDP-9 systems were produced, of which 40 were the compact, low-cost PDP-9/L units.

History
The 18-bit PDP systems preceding the PDP-9 are the PDP-1, PDP-4 and PDP-7. Its successor is the PDP-15.

Hardware
The PDP-9, which is "two metres wide and about 75cm deep," is approximately twice the speed of the PDP-7. It was built using discrete transistors, and has an optional integrated vector graphics terminal. The PDP-9 has a memory cycle time of 1 microsecond, and weighs about 750 lb. The PDP-9/L has a memory cycle time of 1.5 microseconds, and weighs about 900 lb.

It is DEC's first microprogrammed machine.

A typical configuration included:
 * 300 cps paper tape reader
 * 50 cps paper tape punch
 * 10 cps console teleprinter, Model 33 KSR

Among the improvements of the PDP-9 over its PDP-7 predecessor are:
 * the addition of status flags for reader and punch errors, thus providing added flexibility and for error detection
 * an entirely new design for multi-level interrupts, called the Automatic Priority Interrupt (API) option
 * a more advanced form of memory management

User/university-based research projects for extending the PDP-9 include:
 * a hardware capability for floating-point arithmetic, at a time when machines in this price range used software for floating-point arithmetic
 * a PDP-9 controlled parallel computer

Software
The system came with an OS that functions as single-user keyboard monitor, called ADSS (ADvanced Software System). DECsys provided an interactive, single-user, program development environment for Fortran and assembly language programs.

Both FORTRAN II and FORTRAN IV were implemented for the PDP-9.

MUMPS was originally developed on the PDP-7, and ran on several PDP-9s at the Massachusetts General Hospital.

Sales
The PDP-7, of which 120 were sold, was described as "highly successful". The PDP-9 sold 445 units. Both have submodels, the PDP-7A and the PDP-9/L, neither of which accounted for a substantial percentage of sales.