Re: 28-bit LBA BIOS and 48-bit LBA XP - Can I use my 160GB hard disk safely?

"JS" <J@S> wrote in message news:Od5xiX16HHA.4816@xxxxxxxxxxxxxxxxxxxxxxx

I recently upgraded my notebook with a 160GB hard disk. However in BIOS I
see only 137GB. I know it is because the BIOS is only so-called '28bit'
LBA.


How do you know that? How do you know that it's not the lack of SP1 or SP2,
which would have the same effect?


The notebook is of 4 years old and there will be no more BIOS update.
When I install XP (SP2) on this HD, I still see 160GB in XP.


Then it would seem that the BIOS is *not* the issue. If if were, Windows,
even with SP2, could not see the full 160GB.


I heard it is because the driver in XP SP2 (atapi.sys) is 48-bit LBA
already so it can recognize and access all 160GB disk.


You need *both* to be able to access the full size of a drive that large:

1. A motherboard with a BIOS and controller that supports 48-bit LBA (or
alternatively, an add-in controller card that does).

2. At least SP1 of Windows XP.


But does this mean I can ignore the BIOS limitation and fully utilize
160GB in XP? I also heard some people with similar HD upgrade suffered
data loss or system destruction because as something in the system doesn't
support 48-bit, when writing to disk, it wraps back to first tracks and
destroys MBR, boot sectors etc. But I don't know whether it was because
BIOS didn't support 48-bit.


I've never heard of such an issue. As far as I know, if either of the two
items I cited above is missing, you can not get the full drive size. If both
are present, you *can* get the full drive size, without a problem.



So my question is, with 28-bit BIOS, can I safely use 160GB disk with XP
Sp2?
I read many articles, including Microsoft ones, that state that besides
the OS 48-bit LBA support, BIOS must also support 48-bit LBA. But I also
heard that, BIOS is only active when booting up the PC, once it passes to
OS, it should be the OS that manages the disk. So, even though in BIOS I
see only 137GB, it should not affect OS activities as long as OS supports
48-bit LBA.


Not correct. Windows can only see what the BIOS reports to it. *Both* are
required.

--
Ken Blake - Microsoft MVP Windows: Shell/User
Please reply to the newsgroup

So I am a bit confused: As OS can recognize 160GB, why BIOS matters? In
what situation can a 28-bit LBA BIOS destroy a 160GB disk?
I heard that some people say 'as long as the midpoint of the partition
falls below 137GB, the BIOS will be able to boot from that partition'
because the midpoint is where the MFT mirror is stored. But in XP the MFT
mirror is stored at the end of partition?





.

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