Digital Equipment Corporation (DEC) was founded in 1957 and by 1975 had ranges of computers based on 16-bit, 18-bit and 36-bit words. The computers were called Programmed Data Processors or PDPs for short. By 1975, the main member of the 16-bit range was the PDP11. The Atlas Computer Laboratory had the current member of the 18-bit range, the PDP15 used as a 2-person interactive graphics system. The PDP10 was the current member of the 36-bit range. By 1975, the PDP10 had been renamed the DEC10, probably for marketing reasons.
The PDP10 was the successor to the PDP6 and came out in 1967. Bob Hopgood visited DEC in 1967 to see if it was a possibility for the Atlas front-end system. Unfortunately, the system would not be available in the time frame required and the Sigma2 was purchased instead.
The first model was the KA10 which was installed in many universities including UMIST and Edinburgh. A major attraction was the ability to tailor the configuration to meet the local needs with a starting price under $100K. About 250 systems were sold.
The TOPS-10 Operating System was used on both the KA10 and KI10. Both the hardware and operating system had been designed to allow timesharing between users. A fully configured system could handle over 100 users as long as they were not particularly demanding. The KI10 was an integrated circuit version of the KA10 and was nearly twice as fast. It had paging hardware and was introduced in 1972. The amount of virtual and physical memory was restricted to 256K words on the KA10. The KI10 allowed up to 4Mwords of physical memory.
The KL10 was introduced in 1974 and was over 4 times faster than the KA10. In addition, both the physical memory and virtual memory were increased to 4Mwords. It was clearly a strong candidate for the large interactive facility supporting 60 simultaneous users to be installed at Chilton.
Although the original plan was to upgrade the configuration of the UMIST KA10 and upgrade the Edinburgh machine to a KI10, in the end, both machines were upgraded to KI10 systems. At the time DEC had installed about 250 KI10s so the systems were mature and many users were upgrading to DEC10-KL processors.
After discussion with DEC, it became clear that by purchasing refurbished KI10s, it would be possible to purchase KI10s for both Edinburgh and UMIST. A Letter of Intent was sent to DEC in the Spring of 1976 and Bob Hopgood visited Maynard at the beginning of June 1976. DEC had two in-house almost-new KI processors that they used for diagnostic testing and one of these was allocated for shipping to Edinburgh as long as the firm order was received before the end of June. The machine arrived in Edinburgh in late September. The UMIST system was upgraded later. Both machines delivered an excellent service as part of the Interactive Computing Facility throughout their lives.
