pjm@utastro.UUCP (Phillip MacQueen) (07/14/89)
I have a few questions about the execution speed of certain '386 instructions, and about their speed relative to the '286. I'm would greatly appreciate someone explaining them to me. 1) The INT opcode takes 37 cycles on a '386, and 23+m (m=number of bytes in the following instruction) on a '286. I must be missing something because this seems to be a large number of cycles to essentially push three registers and load one. Why are so many cycles used, and why is the '286 so much faster? 2) The same sort of question applies to the IRET interrupt return instruction. It takes 22 cycles on a '386 and 17+m on a '286. 3) The Output-to-Port instruction (OUT DX,accum) takes 11 cycles on a '386, but only 3 on a '286. Why is there such a big difference? 4) Related to question 3 is the Input-from-Port instruction (IN DX,accum) which takes 12 cycles on a '386, and 5 cycles on a '286. The same old question, why such a big difference? I'd appreciate a copy of replies via e-mail, thanks. ------------------------------------------------------------------------------- ARPA: pjm@astro.utexas.edu Phillip MacQueen McDonald Observatory University of Texas at Austin RLM 15-308 Austin, Texas 78712, U.S.A. -------------------------------------------------------------------------------