Re: How to check whethera disk supports 32-bit IO

[Glynn Clements <glynn@gclements.plus.com>]

query wrote:

> >>     I want to know enable 32-bit IO-support on my SATA hard drive
> >> using hdparm . But before I enable 32-bit support , I want to know
> >> whether my hard drive supports 32-bit IO or not.
> >
> > The term "32-bit I/O" relates to communication between the CPU and a
> > PCI IDE controller.
> 
> "The hdpam man page say "32-bit" refers to data transfers across a PCI
> or VLB bus to the interface  card  only ". So , here does the
> interface card is referring to the CPU.

"Interface card" means a card that plugs into a PCI or VLB slot (VLB =
VESA Local Bus, an alternative standard for expansion cards which
superseded ISA but was itself superseded by PCI).

> > The concept isn't meaningful for an on-board controller.
> 
> By On-board controller do you mean to say hardware RAID device or SCSI
> devices and we don't have  to set IO parameter
> in such devices.

I mean an IDE controller that's built into the Southbridge.

In any case, you won't find a SATA controller using 16-bit transfers.

> > As for communication between the controller and the drive, a parallel
> > ATA interface is 16-bit, while SATA is serial.
> >
> >>          *    48-bit Address feature set
> >> (is it telling that the disk supports 48-bit IO)
> >
> > No, it's stating that the drive supports 48-bit LBA addresses. The
> > original IDE standard used 28-bit addresses which limit the size of
> > the drive to 137GB (2^28 512-byte sectors).
> 
> With 48-bit addressing the limit is 144 petabytes . So , does that
> mean we can install hard drive of  capacity  144 petabytes
> if disks of such size are available and the BIOS supports it. Can BIOS
> put a restriction on the maximum capacity of hard drive we

The practical limit is the fact that the largest drives currently
available are around 3 terabytes.

The BIOS is only relevant to booting from a drive; a modern OS such as
Linux or Windows doesn't use the BIOS to access the drive.

In the past, BIOSes were limited to 528MB or 8.46GB or 137GB. This
meant that if you wanted to boot from the drive, you had to ensure
that the bootloader and kernel were stored in the region accessible to
the BIOS (typically by creating a separate boot partition at the
beginning of the disk). Once the kernel was loaded, it would be able
to access the entire drive.

For a (long) list of such historical limiations, see:

	http://www.pcguide.com/ref/hdd/bios/size.htm

-- 
Glynn Clements <glynn@gclements.plus.com>
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