Re: maximum hard drive size in Latitude cpi

Barry OGrady wrote:

> On Wed, 9 Nov 2005 12:33:51 +0100, "Peter T. Breuer" <ptb@xxxxxxxxxxxxxxx>
> wrote:
>
>>Barry OGrady <atheist.xxx@xxxxxxxxx> wrote:
>>> On Mon, 7 Nov 2005 15:46:27 +0100, "Peter T. Breuer"
>>> <ptb@xxxxxxxxxxxxxxx> wrote:
>>>>It's like talking to the wall!
>>
>>> It must be frustrating that some people don't believe you know
>>> everything.
>>
>>It is pretty annoying. The bigger problem is that some people don't
>>understand that not understanding something means that they don't
>>understand what is being talked about.
>
> I understand.
>
>>> So, on my AMD K6/500, which has a 32 gig bios limit, all I had to do to
>>> use the full capacity of my 120 gig drive was to set the jumper on the
>>> driver to 32 gigs, and Windows would see the full size?
>>
>>Windows can see whatever it likes to see - it can talk to the disk as
>>well as I can, if not better. The point is that the bios is not involved
>>in disk i/o. To find out how big a disk is, one only has to ask it.
>
> And yet Windows seems to be unable to see beyond the bios limit.
>
>>>>>> bits allows for 65,535 sectors.
>>>>
>>>>Uh, please stop speaking vaguely.
>>
>>> Sorry. I should have written 65,535.0000
>>
>>That's better.
>>
>>>>"Needed" WHERE? Your o/s is the one that talks to your controller,
>>>>and your controller is the one that talks to your disk. Note that the
>>>>bios is not involved!
>>
>>> What is the cause of the 8, 32 etc limits?
>>
>>8GB? As far as I recall that was the result of insisting on asking the
>>bios for a c/h/s estimate of the size of the disk, instead of asking the
>>disk directly how big it is. The c/h/s nomenclature has field sizes that
>>make arbirarily large head per cylinder and sector per head (or whatever
>>the meaningless things are) numbers impossible, and maybe there's a
>>limit on cylinder numbers too. Thus drives lie and bioses lie using
>>certain conventions to get across their meaning (git wot I men?) if using
>>c/h/s to communicate in. This gave rise to several problems. The solution
>>is "don't do that then", and "just give us the sector count, straight"
>>(LBA). The ultimate solution is "don't ask the bios, then", and "ask
>>the disk instead, silly".
>
> I understand what LBA is about. My 486/66 had LBA but was still
> limited, presumably by the number of bits.
>
>>>>> hence the 48 bits needed for drives over 137 gigs.
>>>>
>>>>Sigh. The appropriate commands sent to/by IDE controllers to disks
>>>>with more than 137GB do indeed require 48 bits or so in their internal
>>>>format. So?
>>
>>> Is that a limitation of the O/S?
>>
>>?? No. It's not a limitation at all - simply a prerequisite, like using
>>electricity.
>
> How would you overcome a 137 gig limit?
>
>>>>>> What the overlay does is to take over the disk I/O with more bits so
>>>>>> it
>>>>
>>>>Nonsense. Complete balderdash. There is no such thing as "take over
>>>>the disk i/o".
>>
>>> Are overlays a con job?
>>
>>There is no such thing in a modern context. It would make sense only for
>>msdos. The o/s is your "overlay" in the sense you mean.
>
> Interesting. I should be able to use a 40 gig drive in my Latitude CPI
> running XP pro without an overlay.
>
>>>>> You are confusing a number of issues. There's a good rundown on this
>>>>> at <http://web.inter.nl.net/hcc/J.Steunebrink/bioslim.htm> with links
>>>>> for more details.
>>>>
>>>>Thank goodness!
>>>>
>>>>> The only time that the number of bits used to count the sectors was an
>>>>> issue
>>>>> was with the 128GB barrier. Prior to that the limit was related to
>>>>> the cylinders/heads/sectors addressing scheme.
>>>>
>>>>> The overlays in general enable logical block addressing on machines
>>>>> whose
>>>>> BIOS doesn't support it directly. They do _not_ fix the 128 GB limit,
>>>>> which needs 48-bit support in the host adapter.
>>
>>> LBA alone does not overcome size limits.
>>
>>LBA means several things. To your bios it means approximately "don't use
>>c/h/s to talk about the disk size". But that's irrelevant to disk i/o.
>>It WOULD mean that you could probably get a decent size estimate out of
>>your bios to about 128GB (random guess).
>>
>>In the context of disk i/o it DOES mean "linear block addressing", and
>>simply means what has always been the way of talking to disks, since
>>msdos went its merry way to the grave.
>>
>>> My 486/66 had LBA.
>>
>>Then you should have used it.
>
> I did, with a 3 gig drive.
>
>>>>> Any current OS should have no trouble querying the disk directly for
>>>>> its parameters once it has gotten its own drivers loaded--actually
>>>>> getting it to that stage is the problem and this had been handled in
>>>>> various ways by various systems, as until the kernel and disk driver
>>>>> are loaded the machine is still running on the BIOS boot code.
>>
>>> Are overlays a con job?
>>
>>In the sense that you appear to think they exist, and maybe do something,
>>yes, you have been conned.
>
> I'll keep that in mind.

Something I think that all the self-proclaimed experts around here ought to
do is take the sophomore or junior level operating systems lab at a
university with a decent computer science department. Once they've
actually written a boot loader they won't be so adamant about how "Windows
can this" and "Windows can that".

The difficulty that the overlook is that Windows doesn't get burned into
firmware and it doesn't load itself by teleportation--it has to be read off
of the disk, and while it is being read off of the disk the machine is
under the control of something other than Windows, specifically it is under
the control of the boot loader built into the firmware on the motherboard,
and that firmware accesses the disk via the BIOS routines and has the
limitatoins of that BIOS. Once the firmware has transferred control to
Windows, _then_ Windows can query the disk for its capacity and respond
accordingly, but until that happens the Windows has no part in the matter.

Linux addresses this issue by having a small boot partition with a copy of
the OS kernel on it, with the necessary drivers built into the kernel.
Novell accomplishes this by using MS-DOS as a second stage boot loader--you
boot DOS, then boot Novell from a folder that has the OS kernel and disk
drivers in it. I'm not sure exactly _what_ Microsoft has done, but they do
seem to have managed to get NT and its descendants to under some
circumstances boot from partitions larger than the BIOS can access--it's my
understanding though that there are limitations on where the kernel and
drivers can be located on that partition--sometimes a defrag can move one
of the files outside of the range that can be accessed using the BIOS
routines and all of a sudden Windows won't boot anymore for no apparent
reason.

Overlays work, but they shouldn't be used until all other options have been
explored, and they should be used with an understanding of how they operate
and what their limitations are and what problems can occur as a result of
their use. For example "fdisk /mbr", a common step in the removal of a
boot-sector virus, usually wipes the overlay and all of a sudden the system
is unusable until the overlay is restored.

Ontrack's latest overlay for Windows does, I am surprised to find, address
the 48-bit issue and support Windows 2K and XP with NTFS (with some
limitations), so they're still working at it--Ontrack's is the one that is
usually bundled with disk drives, but they seldom include the latest
version and it's never full featured.

You might want to google '"Dynamic Disk Overlay" +NTFS' (include the double
quotes, not the single) for more information about this. Also, Ontrack's
page for their latest version is at <http://www.ontrack.com/diskmanager/>.
Note that toward the bottom of the page there is a link to a "tech paper"
that gives the rundown on what the current version can and cannot do.
>
>>Peter
>
> Barry
> =====
> Home page
> http://members.iinet.net.au/~barry.og

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)
.

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