The introduction of the first general purpose microprocessors inevitably led to the first microcomputers around 1975. At the time these systems were of limited utility, and Ken Olsen famously derided them in 1977, stating "There is no reason for any individual to have a computer in his home."[43] Unsurprisingly, DEC did not put much effort into the microcomputer area in the early days of the market. In the 1980s, DEC built the VT180 (codenamed "Robin"), which was a VT100 terminal with a Z80-based microcomputer running CP/M.
It was only after IBM had successfully launched the IBM PC that DEC responded with their own systems. Digital responded by introducing not one, but three incompatible machines which were tied to proprietary architectures. The first, the DEC Professional, was based on the PDP-11/23 (the 11/73) running the RSX-11M+ derived, menu-driven, P/OS. The idea was to introduce a machine that outperformed the PC, but in doing so they created one that was more difficult to learn and use[citation needed] than PC-DOS or CP/M which were more commonly used on the 8080 and 8088 based microcomputers of the time. The DECmate was the latest version of the PDP-8 based word processors, but not really suited to general computing, nor competitive with Wang Laboratories word processing that was becoming popular.
The best known of DEC's early microcomputers is the Rainbow 100, which ran an 8086 implementation of CP/M. Applications from standard CP/M could be re-compiled for the Rainbow, but, by this time, users were expecting custom-built applications such as Lotus 1-2-3, which was eventually ported along with MS-DOS 2.0 and introduced in late 1983. Users also objected to having to buy preformatted floppy disks. Although the Rainbow generated some press, it was unsuccessful due to its high price and lack of marketing and sales support.
A further system was introduced in 1986 as the VAXmate, which included Microsoft Windows 1.0 and used VAX/VMS-based file and print servers along with integration into DEC's own DECnet-family, providing LAN/WAN connection from PC to mainframe or supermini. The VAXmate replaced the Rainbow and in its standard form was the first diskless workstation.
It was only after IBM had successfully launched the IBM PC that DEC responded with their own systems. Digital responded by introducing not one, but three incompatible machines which were tied to proprietary architectures. The first, the DEC Professional, was based on the PDP-11/23 (the 11/73) running the RSX-11M+ derived, menu-driven, P/OS. The idea was to introduce a machine that outperformed the PC, but in doing so they created one that was more difficult to learn and use[citation needed] than PC-DOS or CP/M which were more commonly used on the 8080 and 8088 based microcomputers of the time. The DECmate was the latest version of the PDP-8 based word processors, but not really suited to general computing, nor competitive with Wang Laboratories word processing that was becoming popular.
The best known of DEC's early microcomputers is the Rainbow 100, which ran an 8086 implementation of CP/M. Applications from standard CP/M could be re-compiled for the Rainbow, but, by this time, users were expecting custom-built applications such as Lotus 1-2-3, which was eventually ported along with MS-DOS 2.0 and introduced in late 1983. Users also objected to having to buy preformatted floppy disks. Although the Rainbow generated some press, it was unsuccessful due to its high price and lack of marketing and sales support.
A further system was introduced in 1986 as the VAXmate, which included Microsoft Windows 1.0 and used VAX/VMS-based file and print servers along with integration into DEC's own DECnet-family, providing LAN/WAN connection from PC to mainframe or supermini. The VAXmate replaced the Rainbow and in its standard form was the first diskless workstation.
The construction of Micro Computers
Tommy Flowers spent eleven months (early February 1943 to early January 1944) designing and building Colossus at the Post Office Research Station, Dollis Hill, in northwest London. After a functional test in December 1943, Colossus was dismantled and shipped north to Bletchley Park, where it was delivered on 18 January 1944 and assembled by Harry Fensom and Don Horwood, and attacked its first message on 5 February.
The Mark 1 was followed by nine Mark 2 Colossus machines, the first being commissioned in June 1944, and the original Mark 1 machine was converted into a Mark 2. An eleventh Colossus was essentially finished at the end of the war. Colossus Mark 1 contained 1,500 electronic valves (tubes). Colossus Mark 2 with 2,400 valves was both 5 times faster and simpler to operate than Mark 1, greatly speeding the decoding process. Mark 2 was designed while Mark 1 was being constructed. Allen Coombs took over leadership of the Colossus Mark 2 project when Tommy Flowers moved on to other projects. For comparison, later stored-program computers like the Manchester Mark 1 of 1949 used about 4,200 valves. In comparison, ENIAC (1946) used 17,468 valves, but, unlike Colossus, was not a software programmable machine.
Colossus dispensed with the second tape of the Heath Robinson design by generating the wheel patterns electronically, and processing 5,000 characters per second with the paper tape moving at 40 ft/s (12.2 m/s or 27.3 mph). The circuits were synchronized by a clock signal generated by the sprocket holes of the punched tape. The speed of calculation was thus limited by the mechanics of the tape reader. Tommy Flowers tested the tape reader up to 9,700 characters per second (53 mph) before the tape disintegrated. He settled on 5,000 characters/second as the desirable speed for regular operation. Sometimes, two or more Colossus computers tried different possibilities simultaneously in what now is called parallel computing, speeding the decoding process by perhaps as much as doubling the rate of comparison.
Colossus included the first ever use of shift registers and systolic arrays, enabling five simultaneous tests, each involving up to 100 Boolean calculations, on each of the five channels on the punched tape (although in normal operation only one or two channels were examined in any run).
Initially Colossus was only used to determine the initial wheel positions used for a particular message (termed wheel setting). The Mark 2 included mechanisms intended to help determine pin patterns (wheel breaking). Both models were programmable using switches and plug panels in a way the Robinsons had not been.
Reconstruction
Construction of a fully-functional replica of a Colossus Mark 2 was undertaken by a team led by Tony Sale. In spite of the blueprints and hardware being destroyed, a surprising amount of material survived, mainly in engineers' notebooks, but a considerable amount of it in the U.S. The optical tape reader might have posed the biggest problem, but Dr. Arnold Lynch, its original designer, was able to redesign it to his own original specification. The reconstruction is on display, in the historically correct place for Colossus No. 9, at The National Museum of Computing, in H Block Bletchley Park in Milton Keynes, Buckinghamshire.
In November 2007, to celebrate the project completion and to mark the start of a fundraising initiative for The National Museum of Computing, a Cipher Challenge pitted the rebuilt Colossus against radio amateurs worldwide in being first to receive and decode three messages enciphered using the Lorenz SZ42 and transmitted from radio station DL0HNF in the Heinz Nixdorf MuseumsForum computer museum. The challenge was easily won by radio amateur Joachim Schüth, who had carefully prepared for the event and developed his own signal processing and decrypt code using Ada. The Colossus team were hampered by their wish to use World War II radio equipment, delaying them by a day because of poor reception conditions. Nevertheless the victor's 1.4 GHz laptop, running his own code, took less than a minute to find the settings for all 12 wheels. The German codebreaker said: "My laptop digested ciphertext at a speed of 1.2 million characters per second—240 times faster than Colossus. If you scale the CPU frequency by that factor, you get an equivalent clock of 5.8 MHz for Colossus. That is a remarkable speed for a computer built in 1944."
In November 2007, to celebrate the project completion and to mark the start of a fundraising initiative for The National Museum of Computing, a Cipher Challenge pitted the rebuilt Colossus against radio amateurs worldwide in being first to receive and decode three messages enciphered using the Lorenz SZ42 and transmitted from radio station DL0HNF in the Heinz Nixdorf MuseumsForum computer museum. The challenge was easily won by radio amateur Joachim Schüth, who had carefully prepared for the event and developed his own signal processing and decrypt code using Ada. The Colossus team were hampered by their wish to use World War II radio equipment, delaying them by a day because of poor reception conditions. Nevertheless the victor's 1.4 GHz laptop, running his own code, took less than a minute to find the settings for all 12 wheels. The German codebreaker said: "My laptop digested ciphertext at a speed of 1.2 million characters per second—240 times faster than Colossus. If you scale the CPU frequency by that factor, you get an equivalent clock of 5.8 MHz for Colossus. That is a remarkable speed for a computer built in 1944."
The Cipher Challenge verified the successful completion of the rebuild project. "On the strength of today's performance Colossus is as good as it was six decades ago", commented Tony Sale. "We are delighted to have produced a fitting tribute to the people who worked at Bletchley Park and whose brainpower devised these fantastic machines which broke these ciphers and shortened the war by many months.
