ISC dual boot

[Raymond Nijssen]

brando at uicsl.csl.uiuc.edu (Brandon Brown) writes:
>bill at bilver.uucp (Bill Vermillion) writes:
>>In article <1991Mar4.141901.4772 at ux1.cso.uiuc.edu> brando at uicsl.csl.uiuc.edu (Brandon Brown) writes:
>>>bill at polygen.uucp (Bill Poitras) writes:
>>> 
>>>Well as far as on power-up I believe someone posted a small little "boot menu"
>>>for ISC to boot either to DOS or Unix on the initial boot, but I wouldn't
>>>recommend it, unless you really switch between the two alot. I would use the`
>>>"fdisk" commands on both Unix and DOS to switch between the two.
>>
>>Well I would surely recommend >AGAINST< fooling with the fdisk.  I have
>>seen systems get wiped out with this.  Some systems furnish a dual boot, if
>>not get the one posted here, or do the following (which I recommend to all
>>those I work for who don't want/have the  dual boot option.
>>
>How would simply changing the active partition wipe the disk? Unless you
>delete the partition, what harm could you possibly inflict?

Just changing the active partition allone should be harmless indeed. But
it's not that simple; your disk can be wiped if you use the DOS fdisk;
I have seen some stupid programs, but this one really beats all records.

The very first sector on your disk contains a small program, loaded and
started by the system BIOS. It looks in the 4-entry partition table for
the first entry that has the active bit set; it then skips to the sector 
specified by that entry. However, there is no standardisation about the
order of the entries in the table, e.g. AT&T's fdisk partition table program
starts looking for the active partition at the 4th entry downto the first one; 
DOS starts at the first one. There are lots of scenarios in which this
discrepancy can load to very confusing and dangerous situations.

A bootselector program enables you to choose at boottime via a menu between 
the partition you want to boot from. This program resides in the sector 
containing the partition table, and replaces the program put there by some 
fdisk program.

If you aren't an expert in this field, or don't have a local wizard, I
strongly discourage you to fool around with different fdisk programs or 
bootselectors. 

Anyway, the PD program 'bootsel.zip' at ftp.win.tue.nl works for me
and many others.

| Raymond X.T. Nijssen  | Eindhoven Univ. of Technology                       |
| raymond at es.ele.tue.nl | EH 7.13, PO 513, 5600 MB Eindhoven, The Netherlands |
| "Don't put that on the wall in a tax-payer supported museum!"  Pat Buchanan |
-- 
| Raymond X.T. Nijssen  | Eindhoven Univ. of Technology                       |
| raymond at es.ele.tue.nl | EH 7.13, PO 513, 5600 MB Eindhoven, The Netherlands |
| "Don't put that on the wall in a tax-payer supported museum!"  Pat Buchanan |