#fdisk -e puts us in an interactive edit mode, so we do the following img file without mounting it, saving the attached name such as '/dev/disk2' in the var $ Here's my current attempt at creating the disk: # create a 720k empty img file with all zeros in itĭd if=/dev/zero of=myfloppy.img bs=1024 count=1440 For the MBR to know where to jump to to find the first instruction of COMMAND.COM, it would need to know where COMMAND.COM is stored, which could be anywhere on the disk in the empty space after the FAT, right? When a file such as COMMAND.COM is written to the disk, the FAT is updated with information about where on the disk the bytes are stored. The first 512 bytes of the disk will be reserved for the MBR, then after that a FAT is written down which takes another X bytes of the disk, then after the FAT, there's empty space to put files down. Presumably in that case, the MBR was written to tell BIOS to start execution on the first instruction in COMMAND.COM.įiguring out where the first instruction is seems like it could be complicated because a number of things need to happen (I think.). For example, on a DOS diskette there is/was a COMMAND.COM fiel on it. My basic, simplified understanding of the MBR as that the MBR is the first 512 bytes of the diskette, which specifies how large the disk is, as well instructions that tell the BIOS to jump to the first instruction of a boot loader that'll kickstart the operating system. In the old days on DOS or on Win9x machines, I seem to remember needing to run a format command with some switches on it that would make the MBR on the disk rather than just a FAT table at the front of the disk - though I'm not sure if I'm understanding MBR correctly. I suspect the problem I'm having is in attempting to properly create the diskette image's Master Boot Record (MBR).įor context, here's my understanding of the MBR/boot process works:

iso, but I'm trying this way and would like to at least understand what I'm doing wrong. I'm aware there are other ways to provide bootable disks to V86 such as a hard drive image or a cdrom.

The boot disk I'm attempting to create is an. I'm doing all of this on OSX High Sierra.

I need to do this in terminal (in a bash script). I am trying to make a FreeDOS boot disk with OSX that's compatible with the V86 library.

Dos 7.1 boot disk img