Okay,
I was totally confused about this 1024 cylinder limit thing, because
this meant that you couldn't boot beyond 500mb. Now my older 486 had
this limit, but the laptop I use, I boot redhat 5.2 at 3500meg, with
didn't seem to gel with what other people were saying, so I looked
around the internet for some more info then I came across a bit of tech
stuff, which was aimed at win people, but seemed to answer my questions.
It attached below, but its a bit long. It also mentions the 8 gig limit
that I've heard before, but never really understood.
cheers
Johann
Simon Bayling wrote:
>
> > I have a 14GB disk on which I want to install Win98 together with Red Hat
> > 5.0. I have read that Linux may have problems with accessing large disks
> > where #cylinders > 1024 and I was wondering what suggestions you have on
> > partitioning the disk.
> I thought that the problem was only booting from a partition past
> cylinder 1024, then you'd need to use a boot disk. Not being able
> to access most of a large disk would put linux at rather a
> disadvantage for server type uses whouldn't it?
>
> > Suppose I need about 1GB for Linux. Will these
> > partitions be successful:
> >
> > first 13GB: windows 98
> > last 1GB: linux
> I don't know, if it's a blank drive why not try it and see? you can
> always re-do them.
>
> first 500Mb: Windows dir and assosiated files
> next 1GB: Linux
> last 12.5Gb: Windows D drive.
>
> > or should I put the Linux root partition (incl. /boot) somewhere within
> > the first 1024 cylinders? And what about LILO, do I just install it and
> > leave it or do I have to dig into the lilo.conf file?
> As to lilo, when I installed RedHat 5.0 from a CD, in the installation
> went throug a lot of lilo options, which enabled you to easily select
> which partitions to be available to boot from, and which to boot to
> by default, no need to even know of lilo.conf there.
>
I found this at http://www.webdev.net/orca/fat32x.htm, and although its
aimed at microsoft people,
I think it answers the basic question about booting above 1024 cylinders
Tech talk..
De-mystifying the 8GB limit
by Jeff Rushton, Powerquest Technical Support
As many of our users have found, there seems to
be a "mystical" limit
to how big a hard drive can be used by DOS. At
first glance this
limit seems arbitrary and can be frustrating,
especially with the
sudden glut of 8GB+ drives on the market. There
is, however, a valid
reason behind it.
On most standard IDE drives (SCSI are different
but similar rules
apply) it is normal to have 16 heads and 63
sectors per track.
Cylinders increase as drive size increases. We
are seeing drives with
as high as 24000 cylinders or as low as 50. To
figure the drive's
capacity, multiply the cylinder, head, and
sector numbers together.
Divide the product by 2048. As a formula it
looks like this:
(cylinders * heads * sectors) / 2048 equals
megabytes
This will give you a number in megabytes that
is equal to the size of
the drive. The system uses these numbers to
help it when reading and
writing to the disk.
The first limit comes directly from how these
numbers relate to the
system. The system BIOS's INT13h interface
allows for a maximum of
1024 cylinders, 255 heads, and 63 sectors per
track. The standard IDE
interface allows for a maximum of 65,536
cylinders, 16 heads, and 63
sectors. In order to satisfy the limits of both
of these numbers, the
minimum highest common number for each is used.
This produces a
maximum number of 1024 cylinders, 16 heads, and
63 sectors (504 MB
per the calculation above).
That limit quickly became too restrictive and a
work around method
was developed. It is now possible to
"translate" a drive by
multiplying the number of heads to reduce the
number of cylinders.
For instance, if I had a drive that was 2046
cylinders, 16 heads, and
63 sectors, I could translate it by halving the
number of cylinders
and doubling the number of heads. This results
in a drive that has
1023 cylinders, 32 heads, and 63 sectors.
By using a translator between the IDE interface
and the BIOS INT13h
interface, we can accomplish this translation
and satisfy both
limits. My IDE drive will still have the same
physical number of
cylinders, heads, and sectors that fit within
its limits, but the
numbers reported to the BIOS INT13h interface
will be translated.
This changes our limit to 1024 cylinders, 255
heads, and 63 sectors
(8GB per the calculation above) or simply the
limits that the BIOS
has in the first place. We are now capable of
working with anything
up to 8GB.
There is another place that this limit can be
found. Every partition
table in a PC is set up with the same
parameters. An entry for a
single partition is 16 bytes long. Of those 16
bytes, three are
dedicated to holding the beginning cylinder,
head, and sector of
a partition and three are dedicated to holding
the end cylinder,
head, and sector of a partition. A single byte
can hold a number up
to 255. If this number where strictly adhered
to this would leave a
limit of 255 cylinders, 255 heads, and 255
sectors. Of the heads
byte, this is true. The other two bytes are
manipulated slightly to
allow for different numbers. The sector number
is held in a six
digit binary number and the cylinders in a 10
digit binary number.
To fit this into the byte structure (remember 8
bits to a byte), the
first two digits of the cylinder number are
chopped off and put on
the front of the sector number. Learning to
interpret the numbers can
be interesting, but it effectively gives us a
limit of 1023
cylinders, 255 heads, and 63 sectors. Once
again 8GB.
Now, if these limits look so built in, why are
we seeing people
breaking them? The answer is logical
addressing. All of these
limits are related to the number of cylinders,
heads, and sectors
that can be handled. When you start addressing
a drive with logical
numbers (start counting at the first sector and
keep counting until
you get to the end), much larger numbers are
possible. For instance,
the total number of sectors for a partition is
stored in four bytes
in the partition table. Four bytes allows
partition sizes up to two
terabytes. If we were to always use this
number, then the 8GB limit
would be non-existent.
But the limit persists. This is because all
logical addressing is
done by operating systems. Windows 95, Windows
NT 4.0, and OS/2 Warp
have systems that allow them to address the
drive in a logical
manner. By doing this, all of these operating
systems can break the
8GB barrier. DOS and Windows 3.x don't have
this ability. They
still rely on the traditional cylinder, head,
and sector addressing.
For this reason any program that runs under
these operating systems
is also limited to 8GB unless it has its own
system for using logical
addressing.
--
Johann Kwiatkowski
Spot The Dog Graphics
P.O. Box 79, Moorooka,
Qld, Australia, 4105
mobile 0418 797 419
email: [EMAIL PROTECTED] or
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