The 11/44 in history

Parent Category: Stories Category: My PDP-11/44 Written by Administrator

The PDP-11/44 is an 1979 implementation of the "full" PDP-11 architecture, which was defined first by the 11/70 in 1975. There are many sites descibing the 11/44, note this one for example.

As you can read everywhere:

“The PDP-11/44 was the last PDP-11 built with discrete logic TTL chips”

It is also the last “true” UNIBUS PDP-11 CPU, and DEC made this very clear in the processor name: nothing can be the successor of  “KD11-Z”. Later UNIBUS machines had QBUS Processors and a UNIBUS/QBUS bridge. Hence the ‘44 is an evolutionary dead end, see a family tree here.
On first glance it seems to be a bit outdated: PDP-11 with large scale integrated semiconductors (micro processors) appeared as early as 1975 (LSI-11). The big 32 bit VAX 11/780 on the other hand was already introduced in 1977.

While the 11/44 was technically not very exciting at its time, it is a robust midrange machine. It was rated by DEC to have 0.42 VUP (VAX units of performance). I found no prices, but the CPU was surely less than 40% of a 11/780. It’s unclear to me how many of them were made: my exemplar has serial number 457 and was built in the second half of 1983 (according to the date code stamped on the TTL chips). After this they shipped 100 per year ... this is not impressive, as DEC is estimated to have shipped a total of 600.000 PDPs in 30 years.
On the other hand, the 11/44 is quite a common machine in literature and under collectors. I’d estimate, that there were at least as many as 11/70’s ... around 10.000?

The PDP-11/44 contains technology from several generations: While the CPU and Cache is built completly from TTL-chips (74Sxx), the floating point unit and many disc controllers use  the famous bit slice processor AMD 2901. Memory is MOS: 176 chips per MB. The console logic card contains an 8 bit Intel 8085 micro processor, and so does the VT100 video terminal which was introduced at the same time.
And in 1986 a DELUA network controller was added to my 11/44, which is built around a Motorola 68000. The 68000 is an 8 Mhz 16/32 bit microprocessor and has much more power than the 11/44 CPU it is serving.
This is how technology changed between 1978 and 1985.