changes made for installing z80dos: changes in z80dhdr.lib: base equ 0e400h RTC equ true ;Real time clock BIOStim equ BIOS+4EH ResDsk equ 1 ; CP/M default is disk A for resets Options equ 00000000B ; Enable public file and delay Assembling and creating Z80DOS.SYS (first boot original CP/M): Z80MR Z80DOS MOVCPM 64 * * SAVE 34 CPM64.SYS DDT CPM64.SYS M1180,1185,100 F1180,1F7F,0 Iz80dos.hex R2580 M100,105,1180 G0 SAVE 34 Z80DOS.SYS Transfer Z80DOS.SYS to MSDOS. The making of SUPERDOS.SYS is analoguous. changes in ZCPR.ASM: CPRLOC EQU 0E400H ;FILL IN WITH BDOSLOC SUPPLIED VALUE FENCE EQU ':' ;SEP CHAR BETWEEN DIR FILES insert the fellowing after the first command in routine PRIN1: ANI 7FH This is because ZCPR outputs characters with bit 7 = 1 . MAC ZCPR DDT SUPERDOS.SYS Izcpr.hex R2580 ; now you might overwrite dr's copyright message too G0 SAVE 34 Z80DOS.SYS