TOPS (Total Operations Processing System)
The following information is sourced largely from the Wikipedia page at https://en.wikipedia.org/wiki/TOPS and is reproduced here for informational purposes. No copyright is claimed over this article by Gricers.
Adoption by British Rail
In the mid to late 1960s British Rail was searching around for ways to increase efficiency, and came across the TOPS system in a 1968 presentation by an IBM US Transportation Industry Representative who shortly after formed IBM World Trade Corp's Transportation Industry Centre in Brussels (E. Wrathall). They purchased the system (along with source code, as was typical for such a large mainframe-based system in those days) and implemented it, assisted by Southern Pacific data processing experts. At the time, the British Government operated a "Buy British" policy for the nationalised industries, and the purchase of an IBM System/360 mainframe to operate TOPS had to be approved by the Cabinet of Prime Minister Edward Heath.
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 one to 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. TOPS could not handle this, 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.
TOPS Numbering Under British Rail
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 1000 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 separated 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". However, in some cases, the sequences do not match, e.g. 158/0 numbers start at 158 701.
Locomotives are assigned classes 01–98: diesel locomotives 01–70 (originally 01–69), DC electric locomotives 71–79 (originally 70–79), AC electric locomotives 80–96, departmental locos (those not in revenue-earning use) 97, and steam locomotives 98. One oddity was the inclusion of British Rail's shipping fleet in the system as Class 99. Diesel multiple units (DMUs) with mechanical or hydraulic transmission are classified 100–199, with electric transmission 200–299. Electric multiple units (EMUs) are given the subsequent classes; 300–399 are overhead AC units (including AC/DC dual-voltage units), while Southern Region DC third rail EMUs are 400–499, other DC EMUs 500–599.
More recently, new electric multiple units and bi-mode multiple units have been given the 700 series and new high-speed units have been given the 800 series. Selected numbers in the 900 series have been used for departmental multiple units, mostly converted from former passenger units.
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 because they carried a prefix letter, which was considered part of the number. More recent EMU deliveries have 6 figure coach numbers.
Recent history
TOPS has grown very out of date in recent decades. It is a text-terminal, mainframe-driven system which is regarded as not very user-friendly and hard to use compared with contemporary computer user-interfaces. In addition, it is written in its own programming language, TOPSTRAN (not strictly speaking a separate language but a set of IBM Assembler macros), 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 do not keep information as up to date 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.