#### Back to index | # Info for pdp1

#### DEC PDP-1

Currently supports three images: Spacewar!, Munching Squares and LISP. No
other images are known at the time of writing: I know there were a text editor
(Expensive Typewriter), an assembler/linker (MACRO), a debugger (DDT), and
even a multi-user, multi-tasking operating system (MIT PDP-1 Timesharing
System), but I have no idea where a copy of these programs could be found.

This driver emulates a complete pdp-1 system, including:
* operator control panel
* perforated tape reader and punch
* typewriter for keyboard input and printer output
* optional type 30 precision CRT display
* optional type 15 memory expansion control, with 64kwords of RAM (16 type 12 memory modules)
* optional type 10 automatic multiply and divide
The internals of the sequence break (i.e. interrupt) system are implemented,
but no device has been set up to trigger an interrupt.

Usage Notes:
PDP-1 currently supports a perforated tape reader (punchtape unit #1), a perforated tape punch
(punchtape unit #2), and a typewriter (printer unit #1).
The simplest way to load and run software is to insert a read-in mode tape (.rim files) in
the perforated tape reader and press the read-in switch once (press simultaneously the Control
Panel key (Left Control) and the Read In key (main keypad Return)).
Three dip switches (RAM size, Hardware multiply and Hardware divide) enable or disable computer
extensions. These switches are only read at reset. Therefore, if you edit them, you must reset
the emulator (press F3 in partial keyboard emulation mode) for the changes to be taken into
account.

The "RAM size" switch installs and removes type 15 memory expansion control:
it is disabled when set on 4kw, enabled with 15-bit addresses when set on
32kw, and enabled with 16-bit addresses when set on 64kw. All known programs
work well whether memory expansion control is installed or not. Only LISP can
take advantage of the extra RAM.
The "Hardware multiply" and "Hardware divide" switches enable or disable
the automatic multiply/divide extension. When they are enabled, two pdp-1
machine instructions (namely MUS and DIS) are replaced with two other,
incompatible, instructions (MUL and DIV, repectively). Therefore, programs
which uses the former variant of these instructions require automatic
multiply/divide to be disabled, whereas programs which use the latter require
it to be enabled. In practice, Spacewar! requires automatic multiply and
divide to be DISABLED (i.e. both switches OFF), whereas LISP requires
automatic multiply and divide to be ENABLED (i.e. both switches ON).

For information on pdp-1 operation, you may have a look at:
<http://www.dbit.com/~greeng3/pdp1/pdp1.html>.

History and Trivia :
In 1957, Kenneth Olsen and Harlan Anderson founded a society called Digital Equipment
Corporation (DEC).
In 1960, they started selling the pdp-1. This was a very interesting computer for its time.
First of all it was cheap and fast for its time: about 100,000 dollars, and a theorical maximum
of 0.1 MIPS. It included 4 kWords of RAM, expandable to 64 kWord (as word size is 18 bits,
this makes from 9 to 144 kBytes, which is HUGE for this time): this is an important detail, since,
at this time, cheap computers (e.g. IBM 650) often had no RAM, and used a magnetic drum instead,
which implied extremely long memory access times.
What made it even more interesting was that it was designed to be operated interactively.
It featured an on-line typewriter (i.e. keyboard and printer), and a CRT (which was seldom used
as a computer device at this time). You could even buy an optional light-pen (this device was
the closest equivalent to today's mouse). Along with its simplicity, this made the pdp-1 quite
user-friendly for its time.
The pdp-1 may be regarded as one of the first personal computers, since one person was quite
enough to run and operate it (although, needless to say, its price was not the kind of price
you would expect from a personal computer today).
The pdp-1 attracted the attention of various hackers in MIT. This resulted into the creation
of Spacewar!, which was the first computer-based videogame, but this is another story.
The pdp-1 was a reasonably successful machine: 49 units were sold, which was not as bad as it
sounds for this time. DEC intended to sell variants of pdp-1 with a bigger word size
(pdp-3 with 36-bit words, and possibly other variants (pdp-2???) with 24-bit or 30-bit words),
but it eventually did not. However, it later replaced pdp-1 with other models, including the first
minicomputer (the pdp-8 in 1965), and, by the early 1970's, it had become a major computer
manufacturer, second only to IBM.

created on Wed May 15 07:18:19 2002