Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!samsung!brutus.cs.uiuc.edu!wuarchive!udel!mmdf
From: Peter_Van_Epp@cc.sfu.ca
Newsgroups: comp.os.minix
Subject: Re: 3.5" disks, PS/2 model 50Z
Message-ID: <7942@nigel.udel.EDU>
Date: 11 Jan 90 16:45:00 GMT
Sender: mmdf@udel.EDU
Lines: 41


 
0/90, 32
>>From: paula@BCSAIC.UUCP
>>In article <7546@nigel.udel.EDU> Peter_Van_Epp@cc.sfu.ca writes:
>>.. stuff deleted 
>>
>>This is fine for diskettes with file systems on them, but doesn't do
>>anything for the case where I want to write a tarfile to /dev/at0.
>>All floppy media do not have boot blocks.
>> 
> At present true, but the reason is that MKFS specifically
> overwrites the bootblock that MSDOS Format put there (with the 
> device parameters) with a block of 0's. If MKFS is stopped from 
> overwriting at least the device parameters, any disks parameters
> can be read from floppy.c. Since I have finished and posted my
> mods that do a similar thing for boot block, this is probably my
> next project. Re reading this I just noticed the part about without
> a file system, assuming that the disk has been formatted by MSDOS
> format (and I suspect, for DOS to read it but I haven't tried!)
> there is a "boot block" (without boot code but with the disk parms)
> on Track 0 sector 1 head 0 of the disk (my boot mods depend on
> this fact!), so the block is there unless the disk has been run
> through mkfs as noted above. This is true of Format from PCDOS 3.2
> and 4.01 at least, because I have made bootable disks on all 4
> media types formated with the DOS format command. I would be interested
> to know of any format program (Norton? are there other format programs?)
> that don't do this. 
>
>>------------------------------------------------------------------------
>>Paul L. Allen                       | pallen@atc.boeing.com
>>Boeing Advanced Technology Center   | ...!uw-beaver!bcsaic!pallen
>
>Peter Van Epp
oops! A clear case of engaging fingers before brain! while the stuff
about format is correct, as Paul pointed out (and which I finally 
understood) any program (such as tar ,ar and probably others) which 
choose to write to "file" /dev/fdx is in fact going to overwrite 
the data in the boot sector of the floppy, and since Minix needs to
be able to write the boot sector to make boot disks I can't see any
clean way to make this idea work. Back to the drawing boards for me!