How to mount a 160K disk img formatted in IBM DOS 1.1 format

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RubyTuesday
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How to mount a 160K disk img formatted in IBM DOS 1.1 format

Post by RubyTuesday »

WinImage and various emulators refuse to recognise an IBM DOS 1.1 formatted 160KB disk.

I have seen some BA posts that suggest using img2dsk to convert the image to a 1.44MB floppy, but I've discovered a way to keep the image in 160K format, just by editing the first 32 bytes of the boot sector.

I have imaged a disk that appears to be single-sided, 8-sectored and double-density. So it's 160KB in size.

I can see the first 5 bytes are EB 27 90 08 00 which this site suggests is an IBMDOS1.1 boot sector.
Unlike later versions of DOS, 1.10 (and 1.00) never contained a BPB (though it appears to have a pre-cursor for one) nor what has become the standard Boot Signature (AA55h) at the end of almost every other Boot sector. The differences mean that most utility programs and all the other versions of DOS and any Windows® Operating Systems will consider these diskettes to be incorrectly formatted!
A little more searching got me this post in French AND English, which gave me some clues, so I opened up my Hex Editor...

My image file had the following for the first 32 bytes

Code: Select all

EB 27 90 08 00 14 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
I replaced those bytes with these

Code: Select all

EB 27 90 49 42 4D 20 31 2E 30 20 00 02 01 01 00
02 40 00 40 01 FE 01 00 08 00 01 00 00 00 00 00 
I can now open the image in WinImage :D

vicvan
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Re: How to mount a 160K disk img formatted in IBM DOS 1.1 fo

Post by vicvan »

PCE (IBM PC 5150) supports various Floppy Image.
I don't recommend to use Winimage to dump 5.25 160KB/320KB disks

RubyTuesday
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Re: How to mount a 160K disk img formatted in IBM DOS 1.1 fo

Post by RubyTuesday »

Thanks for that PCE tip - I'll take a look.

Sorry if I wasn't clear - I'm using my Kryoflux unit to dump disks, but I'm using WinImage to browse the dumped image's contents, as it's faster than booting up a VM/emulator.

os2fan2
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Re: How to mount a 160K disk img formatted in IBM DOS 1.1 fo

Post by os2fan2 »

I wrote a rexx script to past in the new bit at the front of the diskette, and winimage opens them nicely.

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