🚀 go-pugleaf

In message <59lcnr$lf5@mippet.ci.com.au> - Antonio Lam
<laman@accsoft.com.au>23 Dec 1996 07:35:23 GMT writes:
> 
> In Australia, one of the leading PC magazine, PC User, comparing
> Win95, WinNT and OS/2 Warp in the Operation System Section of the Vol
> 9 Number 1 January 1997 issue, says:
> 
> "Both OS/2 and NT directly support RAID (redundant array of
> inexpensive drives) for reliable sky's-the-limit storage, while
> Windows 95 doesn't.  On the other hand, OS/2 Warp needs help to handle
> IDE disks larger than 512kb."
> 
> That is ridiculous, 512kb is smaller than space available on the
> floppy disk.  I think he is talking about the 512MB BIOS limitation. 
> Could someone knowledgable write to the editor on "pcuser@apc.com.au"
> and explain to the author what 512MB limit is.

First, there is no 512MB limit in hard drives.

Second, you and the writers at PC User are probably thinking of the
1024-cylinder limit.  On old IDE systems, this works out to 504MB
(defining "MB" as 1,048,576 bytes, as is done by most software; when
"MB" is defined as 1,000,000 bytes, as hard drive manufacturers do,
the 1024-cylinder limit comes to ~520MB on older IDE systems).

Third, the 1024-cylinder limit comes to other values on other
hardware.  [In theory, it COULD come to 512MB with appropriate
settings, but I've never heard of this in practice.]  On modern
hardware, it works out to variable sizes depending on the hard disks
and hardware and/or software settings.  It's usually not even an issue
these days, in fact.  AFAIK, the next point where this will become an
issue with modern EIDE controllers and SCSI host adapters is at 8GB.

Fourth, OS/2 has long been able to handle drives that have more than
1024 cylinders (as reported by the BIOS).  Like *ALL* OSes, it can't
boot from above the 1024-cylinder mark, but OS/2 has been able to
natively use that space since at least version 2.1, probably earlier. 
At that time, DOS users were struggling to overcome the limit, but
OS/2 did it out of the box.  Amazing how the press can twist the
truth.

Fifth, the way OS/2 handles the limit on drives where it exists is to
ignore it; the limit is imposed by the BIOS, and OS/2 doesn't use the
BIOS for hard disk access (usually; at boot time it does, and it will
if you use the IBMINT13.I13 driver, which isn't the default for most
setups).  Therefore OS/2 just ignores the limit, at least when using
HPFS partitions.  DOS, OTOH, uses INT13, and so to get around the
limit it uses special drivers to re-map the drive geometry, which is
what modern EIDE and SCSI sytems do at a lower level.  This re-mapping
is incompatible with OS/2's method of getting around the limit,
however, hence the "OS/2 needs help" claims, since it's then necessary
to get OS/2 to recognize the DOS kludge if both OSes are to use the
same disk.

Sixth, OS/2 has been able to recognize these DOS kludges for some
time, since one of the earlier FixPacks for OS/2 3.0.  This support is
built into Warp 4.0.

Seventh, I've written a mini-FAQ on the subject, available at:

  http://ezinfo.ucs.indiana.edu/~rodsmith/large-drives.html

It includes a link to a site with yet more detailed information, but
less OS/2-specific information.

If you want to forward this message to the magazine, fine; but as I've
not read the original article, I don't want to reply directly.

> laman@accsoft.com.au

+--------------------------------------------------------------------+
| Rod Smith                                 Author of:               |
| rodsmith@indiana.edu                      "Should I Buy OS/2" FAQ  |
| http://ezinfo.ucs.indiana.edu/~rodsmith   "OS/2 Soundcard Summary" |
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