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SubjectRe: IDE Disk Problems
On Thu, 13 Feb 1997, Christian Rienecker wrote:


> Could it be that you are confusing MBytes with MBits ?
> 'Cause even with PIO mode 4 an EIDE bus cannot exceed 16 MBytes/sec
> regardless of where the data comes from.
> Furthermore, according to my sources there is no no SCSI HD which
> exceeds 10 MBytes/sec real transfer (fram disk not cache) despite
> having the theoretical limit of 40 MBytes/sec for an UltraWide controller.

First of all, modern disks have an on board cache, so this speeds things
up. IDE disks mostly have 64-128k cache, SCSI disks mostly have
512K-2048K. This affects measurement, and can give a transfer rate larger
than the physical transfer rate. The physical transfer rate depends on
spindle speed, bit density and encoding format. 10MB/s is indeed a very
fast physical transfer rate even for a high end disk, but I've seen the
numbers 8.5 and 6.5 come by as throughtput rate from disk to controler,
you could theoreticaly get that on a PIO3 IDE disk. Controler cache also
affects the measurement. As for the 32MB, 25 MB and such earlier in this
thread, those are done through the operating system, so there's also some
local caching going on.

In other words: these are really Mbytes, not Mbits.

Hugo Van den Berg -
Phone - +31 (0)30 - 60 25 400
Fax - +31 (0)30 - 60 50 799

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