hyperthreading trivia ... early 70s, I got sucked into helping with hyperthreading effort for 370/195 (that never shipped).
370/195 could run at 10MIPS, but most codes ran at 5MIPs. 195 had our-of-order execution, but didn't have branch prediction or speculative execution ... so conditiional branches stalled the pipeline (had to do careful programming to get 10MIPS, but abundance of conditional branches in most codes would keet machine to 5MIPS). Two i-streams running at 5MIPS would be able to keep machine running aggregate 10MIPS. Idea was to have dual i-stream and registers ... but same single pipeline and execution units ... with instructions flagged as to i-stream. this discussion of end of ACS-360 includes references to hardware muiltithreading patents (and red/blue bit tagging). http://people.cs.clemson.edu/~mark/acs_end.html other acs-360 reference/trivia ... Amdahl says that executives were afraid that it would advance state-of-the-art too fast and company would loose control of the market ... so acs-360 was shutdown. There is also description of acs-360 features that show up over 20yrs later in ES-9000. -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
