Thursday, March 15, 2012


Life in a start-up business is nothing if not interesting and time-consuming.  TraceLink is growing quickly, and we've released several versions of our software to new customers.  While not retro in any computing sense, it has meant that I've not had a lot of time to continue exploring computing history.

The Amiga's are stored away (A stock A4000 with a CF card adapter instead of the HD, and my hotrodded A4000 with its 68060 accelerator and 128MB of RAM and VGA output).  WINUAE sits idle, waiting for my return...

When I have had some time, I have been playing with emulating another machine, much older than the Amiga, which is part of my history.  Once-upon-a-time I owned a PDP-11/40 with some large disk drives and a tape subsystem.  While long ago sold due to space and power reasons, I spent quite a bit of time resurrecting this machine from its fate in the back-room of a high school electronics lab.  The students had not been kind to the PDP, and backplane pins were broken or smashed flat, power harnesses cut, and other damage done on it.  A few months of work and the PDP-11/40 was back in business...

The PDP-11 computers from Digital Equipment Corporation (1970 - 1984) were 16-bit machines with some limited virtual memory capabilities (22 bit and 24 bit extended addressing both existed), large I/O capabilities for the time, and the ability to drive up to 64 terminals at the same time on the same machine when timesharing.  Physically they were large machines, often the size of washing machines or larger.  Disk drives were extremely expensive and fragile at the time, and storage sizes seem laughable given today's multi-terrabyte drive, often only 5MB or so per 14-inch removable platter.

Today's computing resources have advanced now to the point where it is not only possible to completely emulate these old machines, but to do it much faster than the original machine could have possibly run.  SIMH is my tool of choice for configuring a virtual PDP-11, and it emulates multiple CPU and peripheral configurations with ease.

The PDP-11 series ran different OS's for different purposes, unlike most of the home computers to come later.  Some popular systems were RSTS/E (general purpose time sharing), RSX-11M+ (good for larger development efforts and I/O jobs), RT-11 (a real-time OS and single user - much like CP/M and PC-DOS to come later), and of course Unix.  After the PDP-15, the -11 was the place were much of the Unix systems we have today were born.

For fun, I will briefly explore a few of the OS's mentioned above and compare them with our modern systems.  I think it will be especially interesting to see early versions of Unix, and understand how they are both the same and different than our modern versions, such as Linux and even Mac OSX.

Stay tuned!

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