Future Domain SCSI controller for AT bus

[David O'Shea]

There has been recent talk on the net about SCSI controllers Xenix.

Many things have been written, some quite acurate, some quite shrewd,
and some totally wrong.

First, Future Domain sells 2 types of controllers.  One type is a 
multithread capable controller, the TMC-830/840/880 family.
The other type is single threaded, the TMC-870 is this type.

Someone claimed that Future Domain controllers on Xenix were slow.  This
person also said he is using a TMC-870.   He is correct, Xenix with the
870 is slow, we do not recommend the 870 for use on Xenix or Unix.  It is
primarily designed to be a low cost DOS product.

The TMC-830/840/880 performance is very very good on Xenix.  Quite on par 
with the AHA-1540 Adaptec board which has been mentioned in past letters.
These boards support multi-thread operations, as does the driver.  The driver
does not have wait loops in it as someone erroneously conjectured.


End of major advertisement.

Technical Facts:

1) The TMC-830 and TMC-840 can be switched to either interupt 3 or 5.
   The TMC-881 can be switch to any one of 6 interupts.
2) There is no hardware related problem with using a Future Domain 
   board and some type of Western Digital compatible controller. It is 
   software related.
3) Unix in general does not limit users to a single hard disk driver. 
4) SCO Xenix versions 2.2.X do have a single hard disk driver limitation
   based on DOS compatibility.  Strictly speaking, you can have more than
   one hard disk driver, but only one of them can talk to DOS partitions.
   We designed our driver to be able to support the DOS features of Xenix,
   hence our driver must be the ONE DRIVER, and precludes using the AT driver
   simultaneously.  This is a limitation due to SCO's treatment of disk
   partitioning, which was itself derived from DOS's stupid design.
5) The Future Domain controllers run normal Xenix with our driver linked in 
   place of the standard AT fixed disk driver.  Although installation 
   procedures are automated so that the user just has to answer questions,
   the installation takes some time.  
6) The user must have a running AT type fixed disk system running.  Thus
   a ground zero installation requires building a minimum AT-disk system,
   then rebuilding the SCSI system.  This limitation is a legal one.  It
   is illegal for Future Domain to supply a Xenix N1 Boot diskette with our
   software kit.  So the user is forced to build a new one from the one
   supplied by SCO.  This process is automated, but adds approximately 
   30 minutes to the first time installation of Xenix.  These 30 minutes
   compare to the approximately 3 hours it usually takes to install the 
   system.  3 hours or 3 1/2 hours does not matter that much.
7) When Xenix 2.3GT comes out, multiple fixed disk drivers will be allowed.
   At that time:
    a) You will be able to use both your AT-fixed disk and SCSI disks
    b) Your installation time will no longer require the 30 extra minutes.
8) Contrary to some previous comments, SCSI disks in conjunction with the
   TMC-8340 or TMC-840 are much faster than AT-fixed disks and controllers,
   and provide for the very large capacity SCSI disks now on the market.
9) Xenix 2.2.4 has the multi fixed disk driver facilities built into it,
   but this release is only available with Tandy 1000's.

I hope that his anwers some of the conjecture with fact.  I have tried to 
be honest about FDC good and bad points.

David O'Shea
Future Domain Corporation
Tustin, CA.   I can be reach at the above address and at the following: 
eabu110 at orion.cf.uci.edu
!ucbvax!ucivax!eabu110 at orion