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Retrotechtacular: TOPS Runs the 1970s British Railroad [Hackaday]
How do you make the trains run on time? British Rail adopted TOPS, a computer system born of IBM’s SAGE defense project, along with work from Standford and Southern Pacific Railroad. Before TOPS, running the railroad took paper. Lots of paper, ranging from a train’s history, assignments, and all the other bits of data required to keep the trains moving. TOPS kept this data in real-time on computer screens all across the system. While British Rail wasn’t the only company to deploy TOPS, they were certainly proud of it and produced the video you can see below about how the system worked.
There are a lot of pictures of old big iron and the narrator says it has an “immense storage capacity.” The actual computers in question were a pair of IBM System/370 mainframes that each had 4 MB of RAM. There were also banks of 3330 disk drives that used removable disk packs of — gasp — between 100 and 200 MB per pack.
As primitive and large as those disk drives were, they pioneered many familiar-sounding technologies. For example, they used voice coils, servo tracking, MFM encoding, and error-correcting encoding.
The software was written in BAL, the IBM assembly language, although there were a set of macros called TOPSTRAN to make it slightly easier. Originally, each depot was going to get an IBM card reader and punch machine, but these proved to be unreliable in the rugged environment. Instead, each depot had an emulated card reader and punch using a Datapoint 2200 — the famous computer that didn’t use the Intel 8008, but that CPU was made for use in this computer.
In the video, you can see some Datapoint 2200s and card readers in use back at the data center. They even take the cover off one of the Datapoints around the 3-minute mark. The machines had 12K of RAM (on three circuit cards) and two tape drives. Around the 24-minute mark you get a look at a 600 baud, although the railroad apparently only used 200 baud for reliability. They also show a 2,400 baud modem that, we are pretty sure, had to be tuned before use.
The video can’t seem to decide if it is for general audiences or technical people. For example, it describes the tones from the modem and shows block diagrams of many of the systems. There are even some fake oscilloscope traces of modem outputs.
As far as we can tell, some of TOPS is still in use today. We hope some of it has been modernized, though. If you like 1970s mainframes, we’ll go ahead and waste the rest of your day. No kidding. The video doesn’t embed, but you can play it by clicking the picture below.
