Extremely brief history of PDP computers

I don’t know why I started to put this together. These machines fascinate me, because so much of early computing/hacker type culture happened on them. I started writing a table, but realised a timeline would be more intuitive. In this graph, the price is for a minimal configuration and adjusted for inflation. The time is the memory cycle time, a decent proxy for speed.

Some notes:

• The PDP-1 was created mostly as an experiment. At the time, industrial control systems used either humans or complicated contraptions of logic boards to make decisions. Some engineers at DEC wanted to see if there was a customer base willing to use general-purpose computers instead.
• The PDP-4 was a variant of PDP-1 that was a little slower and much cheaper. It was not compatible with the PDP-1. The PDP-4 was upgraded with new chip technology and became the PDP-7, which was then optimised further for cost and speed and became the PDP-9.
• The PDP-5 was created when they realised the PDP-1 and PDP-4 machines were overkill for industrial control systems. By being smaller, it could be much cheaper, at the cost of compatibility with PDP-1 and PDP-4. It was still intended for roughly the same market. The chip upgrade turned it into the PDP-8.
• The PDP-6 was a completely different beast, aimed at a different market. It supported having tonnes of directly-addressable memory, as well as memory protection, so it could be used as a time-sharing system. The amount of memory made it run Lisp well. With the chip upgrade, it became the PDP-10.
• The PDP-11 was a new architecture again, intended to subsume all the previous models, to avoid running three incompatible lines in parallel. There were many variants of the PDP-11, with various performance characteristics and corresponding price points. However, even its most powerful configuration wasn’t powerful enough to attract many PDP-10 users.
• The VAX came much later, but it’s included in the table anyway because it is what eventually subsumed the PDP-10. The VAX was somewhat compatible with the PDP-11, but they served different markets.