Subject: Qs about Linux setup on Compaq 486 notebook

From: Bhaskar Manda <[email-masked]>
Date: Wed, 28 Aug 1996 14:13:54 -0500

I'm want to use Linux on a Compaq 486/25SL notebook. I'm stuck on
the following issues and would appreciate any pointers.
1 I believe the video ROM is being shadowed. The BIOS setup
 has options to shadow the video ROM at two different addresses,
 but none to turn it off.
2 Some memory is reserved, presumably for shadowing arcane stuff,
 including but not limited to battery management pop-ups (or is that
 in the video RAM?).
3 Who is reserving this memory? Does the BIOS do it? Or is it DOS?
 Since Linux (Debian) install instructions ask you to turn off all
 shadowing, I can do that automatically if DOS is doing the shadowing,
 but I get the impression that the BIOS does this. The how do I go
 about disabling shadowing and not reserving memory?
4 These machines were supposed to have a small partition with
 diagnostics programs on it. I don't see anything but a Big-DOS
 partition with FIPS and other HDD utilities. Can there be a parition
 that such an utility cannot see? 
5 Some utilities I have used show 256k video RAM, but there's supposed
 to be 512k. The same utilities see 16450 UARTs on my serial port and a 
 16550A on the modem board, but MSD sees 8250s on the serial port.
 How reliable is this stuff? Are there definitive h/w utilities in Linux?
6 After resizing partitions using FIPS, the installation boot disk
 vomits a hda: read_intr: 0x40, but I figure that's because of wrong
 information in the BIOS.

I'm looking at the Troubleshooting info in the LDP and the PC h/w faqs.
Any information will be highly appreciated.
Thanks,
-bhaskar

---

From: [email-masked]
Date: Wed, 28 Aug 1996 19:30:34 -0400 (EDT)

Re: Qs about Linux setup on Compaq 486 notebook

I've seen the cautions about shadowing, but have never been bothered by
the existence of it on my system (an AMI BIOS, several years old now).
I've run all the Linux's available including Redhat, Debian, Slackware,
Minilinux, etc, and had no problem from it with any of them.  The reason:
Linux doesn't use the normally shadowed memory addresses.  It avoids the
total 384K of memory completely (!) on most distributions of the kernel
it is unused and marked reserved.  It is not used.  However, there are
some that attempt to use portions of it, such as LinuxLite, to enable them
to run on very low memory configurations.  Otherwise, you should not have
any grief from this at all.

Now, you mention a potential for problems with some laptops.  Many vendors
DO reserve portions of the "upper memory area" (that 384K normally used for
hardware options, shadowing the ROM's, etc, for special purposes that are
intended to improve the performance of the laptop or notebook.  In some
cases this memory can be recovered by the user, and in others it cannot.
With some laptops, this could render the machine useless I suspect, but 
with most it should be of little consequence.

Its almost always the BIOS functionality that does this, and on many it is
done to provide additional cache to improve the disk performance, etc.

Well, as I said above, it might not be a debilitating problem.  On some 
models it could be.

Sure, DOS can only see certain types.  For instance, it can't see a Linux
partition either!  Its just like it doesn't exist.  However, you should be
able to see it using Linux's fdisk.  The problem there of course is you'll
have to be running Linux to be able to use it!  You could install something
like Minilinux using an umsdos file system (installs to a directory on an
existing FAT partition).  Its actually quite small (only will use about 40
megs).

Video RAM is troublesome.  Always has been, for any system.  Linux's
setserial utility will tell you exactly what they are.  It works.  MSD does
report certain "emulations" of 16450 as 8250, and many do not pass muster
for the 550 either.  There are many 16550 "compatibles" and emulations that
are not really 16550's.  Thats also common.

I don't have any idea what you mean by this, so can't comment.