On many of the operating systems, you don't have to do a SYSGEN - just tweak a number in the configuration word and viola, it's now a 50Hz machine. For an RT-11 machine, in particular, you can tweak this on a running system if you wish: .type 50hz.mac .MCALL .PVAL, .EXIT ; RMON Fixed offsets CONFIG = 300 ;Configuration word 1 CLK50$ = 000040 ;50-cycle system clock HZ50: .PVAL #AREA,#CONFIG,#CLK50$,BIS ;Get configuration word .EXIT AREA: .BLKW 4 .END HZ50 .macro 50hz .link 50hz .show conf RT-11FB V05.07 Booted from DU1:RT11FB USR is set SWAP EXIT is set SWAP KMON is set NOIND MODE is set NOSJ TT is set NOQUIET ERROR is set ERROR SL is set OFF EDIT is set KED FORTRAN is set FORTRA KMON nesting depth is 3 CLI is set DCL, CCL, UCL, NO UCF PDP 11/84 Processor 2048KB of memory Floating Point Microcode Extended Instruction Set (EIS) Memory Management Unit ECC Memory Cache Memory PMI Memory 60 Hertz System Clock FPU support .run 50hz .show conf RT-11FB V05.07 Booted from DU1:RT11FB USR is set SWAP EXIT is set SWAP KMON is set NOIND MODE is set NOSJ TT is set NOQUIET ERROR is set ERROR SL is set OFF EDIT is set KED FORTRAN is set FORTRA KMON nesting depth is 3 CLI is set DCL, CCL, UCL, NO UCF PDP 11/84 Processor 2048KB of memory Floating Point Microcode Extended Instruction Set (EIS) Memory Management Unit ECC Memory Cache Memory PMI Memory 50 Hertz System Clock FPU support -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927