I ran my own blog from November 2006 till October 2014. All posts are still online, but I don't have time to update it anymore. Please note that all images and media files have been removed when the backup was moved to a new host in early 2016. Enjoy!

Cray-1: A Supercomputer Way Ahead Of Its Time

20. november 2007

The Cray-1 was a supercomputer developed during the early 1970's by Seymour Cray and his company Cray Research, it is considered to be one of the most famous and successful supercomputers of all times. The specs were extraordinary in 1976: the Cray-1 was a 64-bit system running at 80 MHz, addressing was 24-bit for a maximum of 8 MB of main memory.

High performance microprocessors didn't exist yet, therefore the new machine used a large number of high speed integrated circuits (ICs) with a total of about 200,000 gates, a complexity comparable to the Intel 80386 which became available 10 years later. The main register set consisted of eight 64-bit scalar registers and eight 24-bit address registers, plus 64 shadow registers and eight 64 bit vector registers. The system contained four buffers that could pipeline 64 instructions and feed the 12 functional units.

The indicated performance was 160 MIPS, when execution real world applications the system generally offered a performance of about 136 megaflops, with peaks of up to 250 megaflops when running highly optimized software. Since 1978 the Cray-1 was running the Cray Operating System (COS), later machines were running UNICOS, Cray's UNIX derivate.

A major design problem was the signal speed between the different modules and boards, therefore the system included a lot of hardware to delay signals, cables were cut to very specific lengths in order to avoid electrical reflections and the entire chassis was bent into a large C-shape so that wire-lengths were shorter. The system weighed 5.5 tons including the freon refrigeration system, the complete system consumed an incredible 250 kW of power when running. 

Today a common Mac or PC is about 100 times faster than a Cray-1.