booting DOS on ISC+SCO, and DOS filesys handling (long-ish)

[Thomas Hoberg]

In article <1991Apr24.074220.17639 at jet.uucp>, cm at jet.uucp (colin manning) writes:



|> Ideally, there would not be all these seemingly unnecessary restrictions
|> concerning support for different partition types, sizes etc. In my opinion,
|> whoever designed the fdisk partition table structure left a lot to be
|> desired - why only allow at most 4 partitions on a drive ? and why restrict
|> the cylinder numbers to 10 bits ? It seems to me that to have allowed a 
|> reasonable number of partitions (say 32) and to use 32 bit disk addressing
|> would not have been too hard. The cost would have been, say, an additional
|> 256 bytes or so to save a lot of hassle.

I thank God they included the partition table at all. Remember that the partition
table first appeared on the IBM PC/XT with DOS 2.0. The XT had a 10MB hard disk
and for operating systems there was DOS, DOS and DOS. CP/M-86 was dying and Xenix
was "announced" (it never *really* materialzed for the 8088, just like the 
multi-tasking DOS 2.5)

|> 
|> Also, why is it that support for DOS 4 partitions is non-existant in ISC and
|> SCO ? DOS 4 seems to have been around for quite long enough for support to
|> have been added.

Most people could live with 32MB DOS partitions and many without any.

|> 
|> Anyway, I'd be interested in information on any of the following. I'll 
|> post a summary in due course if there's sufficient interest.
|> 
|> 1. Is it possible to have an easy way of selecting between booting DOS
|>    or Unix on an ISC system, without having to remember to use fdisk 
|>    every time to change the active partition ? Ideally the source to 
|>    a boot program that could be put on a primary DOS partition would
|>    be nice (like the one I use with SCO).

I posted a partition booter some time ago, but BOOTMENU seems to have take over
the market. 

|> 2. Although ISC and SCO do not seem to have any support for >32Mb DOS 4+
|>    filesystems:
|>    i.  When is support for these expected from ISC and SCO ?

Perhaps never, but while they are at it, why not add High Sierra, HPFS, Mac-FS,
VMS, 370, Cyber, creeping featureism and melancholia.

|>    ii. When you use SCO, and you interrupt the auto-boot to boot DOS (by
|>        typing 'dos' at the : prompt), will it boot correctly off a >32Mb
|>        DOS 4 partition ?

I hope so.

|>    iii. If you try to have >32Mb DOS 4 partitions on a SCO or ISC system,
|>        does the Unix safely ignore them even though they cant use them ?
|> 

Yes

|> 3. Is it possible to have both SCO and ISC Unix on the same machine, in
|>    different partitions, and have some way of selecting between the 2
|>    at boot time ?

ISC (and DOS 5) depend on their partitions to be active to boot. I don't know
about SCO. If your partition booter rewrites the partition table it should work.

|> 
|> 4. Does ISC recognise SCO partitions and vice-versa ?

Both recognize Xenix file systems. ISC FFS and SCO 1k file system might use
different magic numbers.

|> 
|> Many thanks in advance,
|> 
|> -- 
|> - Colin Manning, cm%jet.uucp at ukc.ac.uk (world) OR cm at jet.uucp (UK only)
|> - Disclaimer: Please note that the above is a personal view and should not 
|>   be construed as an official comment from the JET project.

-- tom
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