TOPS (Total Operations Processing System)
In the early 1960s the Southern Pacific Railroad, ahead of the pack in its embrace of technology, developed a computer system they named TOPS, which officially stood for Total Operations Processing System. The intention was to take all the paperwork associated with a locomotive or railroad car - its maintenance history, its allocation to division and depot and duty, its status, its location, and much more - and keep it in computer form, constantly updated by terminals at every maintenance facility. On paper, this information was difficult to keep track of, difficult to keep up to date, and difficult to query - the only way to do that would be a whole lot of phone calls. Computerising this information enabled a railroad to keep better track of its assets, and to utilize them better.
One way to offset the development costs of such a system, of course, was to sell it to other systems, and the Southern Pacific did just that. A fair number of American railroads took to the system, as did many systems around the world.
Adoption by British Railways
In the mid to late 1960s British Railways (soon to become British Rail) was searching around for ways to increase efficiency, and came across the TOPS system being used by the Canadian National Railways. Finding themselves rather taken with it, the system was purchased (along with source code, such as was typical for such a large mainframe-based system in those days) and was slowly implemented on British Railways.
The adoption of the TOPS system made for some changes in the way the railway system in Britain worked. Hitherto, locomotives were numbered in three different series. Steam locomotives carried unadorned numbers up to five digits long. Diesel locomotives carried four digit numbers prefixed with a letter 'D', and electric locomotives with a letter 'E'. Thus, up to three locomotives could carry the same number! This TOPS could not handle, and it also required similar locomotives to be numbered in a consecutive series in terms of classification, in order that they might be treated together as a group.
Sequentiality was all that was required, but with the requirement to renumber, it was decided to adopt a logical system for classification, and the five or six digit TOPS number was divided into two parts. No class of locomotive or multiple unit numbered over a thousand examples, so the last three digits were used for the individual number (between 001 and 999) in that class. The first two or three digits were used to denote the class of locomotive or multiple unit. The numbers were often written in two space seperated groups, such as '47 401' to highlight that division, but the TOPS system actually stored and displayed them without the space - '47401'. Sub classifications were indicated in the TOPS system with a slash and a subclass number - e.g. '47/4'. It was convention - though not enforced within the TOPS system - that subclass numbers were boundaries in the locomotive numbering system, such that class '47/4' started with number '47 401'. If there were more than 99 numbers in a subclass, the number series extended to the next value of the third digit; thus, since there were more than 200 locomotives in class '47/4', subclasses '47/5' and '47/6' did not exist, and the next valid subclass by convention was '47/7' starting with '47 701'.
Locomotives are assigned classes from 01 to 99, with diesel locomotives assigned classes 01 to 69, DC electric locomotives between 70 and 79, and AC electric locomotives 80-99. Diesel multiple units (DMUs) with mechanical or hydraulic transmission are classified between 100 and 199, while those with electric transmission are between 200 and 299. Electric Multiple Units (EMUs) are given the subsequent classes; 300 to 399 are overhead AC units, while Southern Region 600-volt DC third rail EMUs are between 400 and 499, with other DC electric units between 500 and 599. Classes above that have not yet been used.
Coaching stock and individual multiple unit cars are allocated five digit numbers; since the early 1980s it has been forbidden for them to have the same numbers as locomotives, but before then duplication was possible.
Locomotives began receiving their TOPS numbers in 1972, while EMUs and DMUs didn't receive TOPS unit numbers until later. Some locomotives which were slated for withdrawal never received a TOPS number and operated until the late 1970s with their old D-prefix numbers.
Locomotive and Unit Classification
Locomotive classification is covered under TOPS locomotive classes (currently a nodeshell). I may produce similar writeups for multiple-unit classification in the future also.
TOPS has grown very out of date in recent decades. It is a text-terminal, mainframe-driven system which is very user-unfriendly, cryptic, hard to use and prone to operator error (because of its cryptic displays and command set). In addition, it is written in its own programming language, TOPSTRAN, and it is increasingly hard to find and train developers to maintain it. The division of British Rail and privatisation has also hurt TOPS, because it was never really designed for that; some Train Operating Companies don't keep information as up to date in it as they should.
Attempts have been made to 'skin' the system with a more user-friendly interface, called TOPS 2000; in addition, there are other parallel systems now, such as TRUST and Genius, but none has yet supplanted the TOPS system. Eventually, no doubt, they will.
For anyone obsessive about trains in Britain, of course, access to the TOPS system is the holy grail; knowing what locomotive is where, what trains it's going to work, that kind of thing. The catch is, of course, that the system is considered company confidential and the information within it is not generally considered available for the general public. They might, after all, find out the REAL reason why their trains were late ...
Therefore, the best way to get access is to work for a railway company and have access through one's work. The second best is to have a friend in that situation! Care, of course, has always been required; accessing TOPS for personal reasons has, when found out, sometimes resulted in disciplinary action or dismissal, though generally only flagrant violators have been so punished.
With help from many sources, in particular an article at the European Railway Picture Server http://mercurio.iet.unipi.it/, pages at the Rail Enthusiast Web Sites at http://www.trainweb.org/rews/ and many postings on the Usenet newsgroup uk.railway.