> If the drive does not use buffered seek, it is
necessary to transfer
> a new cylinder's data into the buffer RAM in less than the seek time.
> As far as I know, the highest capacity 5.25-inch Winchester drives that
> did not use buffered seek had no more than four heads, 615 cylinders,
> and no less than 20 ms seek time, so the maximum transfer rate needed
> to transfer data to and from the backing disk is about 33 MB/s. This
> would require RAM with a 30 ns cycle time. More practically, the
> buffer RAM could have a x16 or x32 organization, stretching the
> cycle time requirement to 60 ns or 120 ns.
"James Dickens" <jdickens(a)ameritech.net> wrote:
okay not an expert, but most systems using these
drives used interleaving
sectors(because there was no way the system was fast enough to handle the
data), the IBM PC used a factor of 6.
Interleaving by the host is completely irrelevant to the disk emulator,
which doesn't even have a concept of "sectors". To the disk emulator,
a track is just a big collection of samples of the data line, which
don't even have a 1:1 correspondence with host data bits (or even host
channel code bits).
The machine the device would not
what to do with 30MB/s of data if you produce it.
The 33 MB/s I quoted was the necessary transfer rate between the buffer
memory and the drive *inside* the disk emulator. It has nothing to
do with the host computer.