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     Speed considerations

       A small maximal speed table for the SCSI transfer modes could
       read like this:
        Transfer type           Bits    Speed/Data rate

       Asynchronous             8       3.3 MBytes/sec
       Synchronous              8       5.0 MBytes/sec
       Fast Synchronous         8      10.0 MBytes/sec
       Wide Synchronous        16      10.0 MBytes/sec
       Fast Wide Synchronous   16      20.0 MBytes/sec
       Wide Synchronous        32      20.0 MBytes/sec
       Fast Wide Synchronous   32      40.0 MBytes/sec

       When reading things like "data rate buffer-to-bus 10 MB/sec"
       with SCSI devices, keep in mind that this doesn't mean the real
       sustained data rate your hard disk or CDROM can deliver -
       it's just the speed the device can post its cache contents to the
       SCSI bus. With hard disks, you will mostly find statements like
       "internal data rate 30-47 MBit/s", what would mean in this
       example, the disk drive could  transfer  5,875  MBytes/sec  raw  data
       internal. But this value  cannot  be  reached  -  you'll  loose  some
       speed due to the disk architecture: If you have a disk drive with 60
       sectors per track and 5400 rpm, the value could be not better than:  (
       sectors * bytes/sector * rpm ) / seconds per minute,
       (60    *    512        * 5400) / 60   = 2,765 MBytes/sec
       Add to this some command overhead, head movement times and so  on,  then
       you get an impression, how realistic these values are ...