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Date:	Thu, 23 Oct 2003 08:22:11 PDT7
From:	Peter Skye <pskye@peterskye.com >
Reply-To:	scoug-help@scoug.com
To:	scoug-help@scoug.com
Subject:	SCOUG-Help: System files, MBRs, boot managers (was: sysinstx ?)

Content Type: text/plain

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Steve Carter wrote:
>
> All this DOS stuff makes my head hurt.

All the bars in San Diego make _my_ head hurt, although there seems to
be a few hours' delay between holding the glass and holding my head.

> Programs compressed with PKLite for DOS can be expanded with:
>
> CAUNLITE.EXE 17,376 1-01-93
> DISLITE .DOC 19,337 4-14-92
> DISLITE .EXE 17,358 4-14-92

Can you send them to me privately? I'm really curious what's inside
SYS.COM.

> I believe that SYS.com merely placed copies of MSDOS.SYS
> and IO.SYS (or their equivalents in the IBM/DRDOS world)
> in the correct locations, i.e. the _VERY_ first entries
> in the FAT 16 partition. The MBR loader was not smart
> enough to find them otherwise.

I just took a look and, yup, IO.SYS and MSDOS.SYS are the very first two
entries in my DOS partition. I don't think I ever knew that.

> Traditionally, the MBR took up just one sector, the very
> first one on the disk. The partition table was at the end
> of that sector, and defined the four possible partitions.

Yes. Space for four partition specifications plus a checksum byte.

> So boot code was limited to well under 512 bytes.

I disassembled the boot code once. Even though I've written assembler I
was still impressed with how much you can do in a couple hundred bytes
of machine code.

> The other sectors in cylinder 0 were vacant. Partitions
> start on a cylinder boundary. This leaves considerable
> room for both boot sector viruses or boot managers to
> locate additional code for a more complicated procedures.
> I think PowerQuest's PQBoot is such a product, as opposed
> to IBM's Boot Manager which requires a partition.

I forgot about those boot viruses, thanks. Yes, the entire first
cylinder is available for boot-up code.

There are a whole bunch of "boot managers" and they aren't OS-specific
so they should all work with vanilla OS/2 (although System Commander is
file-system specific because it stores control files in a
subdirectory). Note that the usual restrictions may apply depending on
what the programmer allowed -- booting to huge drives, booting to other
physical drives, booting to logical partitions, booting to an LVM
volume.

Here are the ones I know of (I bought all the cashware ones). I'll post
the links if anyone wants them.

AiR-BOOT - has OS/2 options, supports LVM
Boot Manager (IBM)
Boot Manager (PowerQuest)
BootMagic (PowerQuest) [same as their Boot Manager??]
EZ-Drive (loads before the boot loader)
GRUB
LILO
Maxtor's MaxBlast (loads as a "pre boot-loader")
Power Boot and Power Bios Lite (BlueSky Innovations LLC)
Ranish's Boot Manager
ShellCity's "Other Operating Systems"
System Commander (V Communications)
XOSL (Extended Operating System Loader)

Many people don't know you can use the "boot loader" sequence to extend
your computer's functionality. For example, if you wanted to boot over
a dynamically-secure network then you could use the boot loader cylinder
to hold the required security, encryption, mac and network code.

- Peter

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