X86 jump (was: Formatting and verifying MFM hard disks

Exactly. (JMP C800:0005) <pedantic> EAh is a "far jump", 5 bytes, with offset and segment specified. (Don't forget that intel is Least Significant Byte first) But also be aware that there are many other jumps in x86: "near jump", 3 bytes, with offset specified for jumping within the segment currently specified in CS "Short jump" or "relative jump", 2 bytes, with a range of 128 bytes from current location "Conditional jumps", 2 bytes, which are all relative, and jump or don't jump based on various flags "CALL"s, both near and far, which push the IP and jump "Int", which pushes the flags, turns of interrupts, and looks up far jump destination in the Interrupt Vector Table By writing such a jump program and putting it into the boot record of a floppy disk, then you can format drives for use with other OS's without having to go near PC/MS-DOS or WINDOZE. But, if you are going to boot DOS, . . . DEBUG is the most powerful and useful program that MICROS~1 has ever provided. It is present in EVERY version of MS-DOS and WINDOZE. For formatting a drive, it is handier to have than just the jump program, since you can use it for the jump, use it to disassemble the ROM (if you have a controller that puts the routine at a different address), read and write disk sectors (it assumes a DOS disk), view or edit RAM, or use it to write ANY program (such as a better OS). </pedantic> On Fri, 28 Nov 2003, Geoff Reed wrote: