Amiga 2000 Bridge Card Hard Drive Performance

        These are the results of some interleave adjustment experimenting I 
      did on my Amiga 2000.  I found that the proper adjustment can make a
      BIG DIFFERENCE in hard drive performance.  Pleading ignorance and 
      just accepting the defaults are a good way to insure sub-standard 
      performance.

        My particular setup is as follows:

                  Amiga 2000 equiped with bridge card.
                  Western Digital hard drive controller
                  Miniscribe 8438 32meg hard disk drive (mini 3 1/2 inch
                      mounted inside Amiga in second drive bay.

        By adjusting the interleave value I was able to increase my data
      transfer rate by 567%.  That's nearly a six to one increase!

      Interleave | Revolutions  | Tranfer Rate | Comments
        Value    | Per Cylinder |   In Bytes   |
      ------------------------------------------------------------------
          2      |      18      |    29,002    | Unusually long low
                 |              |              |   level format time
          3      |      18      |    29,002    |
                 |              |              |
          4      |      17      |    30,317    | Default in format setup
                 |              |              |
          5      |       3      |   174,080    | Optimum for my setup
                 |              |              |
          6      |       4      |   130,560    |
                 |              |              |
          7      |       5      |   104,448    |
                 |              |              |
          8      |       5      |   104,448    |

        As can be noted in the chart above too tight an interleave (small 
      value) can cause far worse performance than too loose (large value).

        The results can be anticipated because most PC/XT running at 4.77mhz 
      should be have their hard drive formated at an interleave of 5.  Only 
      8mhz PCs usually are formated at 4.  This is only in general as the 
      particular system as a whole (computer, controller & drive) affects 
      the outcome.  Only by experimenting can the exact value be known for 
      sure but a little too loose is a lot better than a little too tight.
      If in doubt set it looser (larger interleave value).  An interleave of
      6 should be good for all but the strangest of setup.
        In the IBM PC Hardware SIG Disk data library are several programs to 
      assist in finding the proper adjustment.  Beware of programs however
      that optimise the interleave for you.  I have found none that work
      with a bridge card).
        The interleave settings for SCSI controllers are just as critical
      as I have found when working with UNIX workstations.  Presently I do
      not have a SCSI drive in my setup but I would hope by the time I do
      some programs such as I found in PC SIG would exist for the Amiga.  I
      am somewhat doubtful that the manufacturers can be counted on to
      insure maximum performance.  This is especially true considering some 
      of the more unique systems that can be made with an Amiga (68020-30
      at greater than standard speeds).
                         
                                      Mark A. Raschke
                                      Compuserve - 72416,2511
                                      GEnie      - M.A.Raschke