Discussion from last month of #VAX #history and #Mashey’s explanation of its demise.
on 02025-10-05#PDF #paper of Bhandarkar and Clark’s comparison of the #ISAs and #performance of #VAX and #MIPS from 01991. #history
on 02025-10-05#VAX #asm return instruction is rather hairy: “SP is replaced with FP plus 4. A longword containing stack alignment in bits 31:30, a CALLS/CALLG flag in bit 29, the low 12 bits of the procedure entry mask in bits 27:16 and a saved PSW in bits 15:0 is popped from the stack and saved in a temporary (tmp1). PC, FP and AP are replaced by longwords popped from the stack. A register restore mask is formed from bits 27:16 of tmp1. Scanning from bit 0 to bit 11 of tmp1, the contents of the registers whose numbers indicated by set bits in the restore mask are replaced by longwords popped from the stack. SP is incremented by bits 31:30 of tmp1. PSW is replaced by bits 15:0 of tmp1. If bit 29 of tmp1 is 1 indicating a CALLS was used) a longword containing the number of arguments is popped from the stack. Four times the unsigned value of the low byte of this longword is added to SP and SP is replaced by the result.”
on 02025-09-09some notes on the #VAX’s notorious floating-point evaluate-polynomial instruction
on 02022-10-12John Mashey on #RISC vs. CISC and in particular why the #VAX was doomed. #architecture #history
on 02022-10-12John Mashey in 02005 commenting on #performance #history and why it was so hard to make a fast #VAX
on 02021-02-09