🚀 go-pugleaf

In the September batch of Tech Notes, #159 finally addresses
the issue of "How do I build my own SCSI drive?"  I would say,
overall, it's no more encouraging than, say, writing your own
printer driver.

I suppose this is yet another confirmation that the Mac is
a business PC, not a hacker's PC.  It's hard to imagine that
a for-profit company would make any other choice.

___________________________________________________
Macintosh Technical Notes


#159: Hard Disk Hacking


See also:	Technical Note #96QSCSI Bugs
		Technical Note #134QHard Disk Medic
		Device Manager

Written by:	Bo3b Johnson	September 1, 1987
___________________________________________________
For those of a technical bent with some extra time,
you can build your own hard disk system from a cheap
SCSI drive and a driver that you write.  This is not
a project for those short on time, so beware.
___________________________________________________

We often get questions regarding the feasibility of
connecting a TgenericU SCSI drive to the Macintosh,
usually the Macintosh II.  It is possible to use a
standard drive, but it is important to be aware that
there is a reason why a fully assembled drive costs
more.  When buying a hard disk you have two choices:

	1) buy a fully assembled drive, formatting and
driver software included

	2) buy the pieces necessary to assemble your
own:  the drive itself, power supply if needed,
cables, and development system to write a driver and
formatter.

The second choice will often appear to be cheaper,
since you donUt have to pay for a fancy case with a
fancy label.  However, you are also missing the
chance to pay for some fancy software that took some
fancy amounts of time to write.

Do not underestimate the difficulty of building your
own hard disk.  SCSI drives are only partially
standardized so a driver written for one drive will
probably not work (at least not well) on another
drive.  All drives come with a formatting utility
that also contains a driver for reading and writing
sectors to the disk. For example, the Apple drives
come with a program called HD SC Setup.  Most
third-party drives have a similar utility that is
specific to their drive.  The formatting operation
varies widely depending on the drive, and the driver
also may have to know about specific timing problems
with a given drive.  HD SC Setup can only support
the drives which we produce.  

If you decide that you want to hack together your
own drive, you will need to write this
formatter/driver program.  It is non-trivial, and
this is part of what you pay for when you buy an
off-the-shelf drive.  If you have the time, you may
save some money.  If you are writing your own
formatter/driver program we can help you with
problems you run into, but you must be familiar with
SCSI terminology, the SCSI Manager, and be able to
use an assembly level debugger like Macsbug or TMon. 
You may run into timing difficulties that require
the use of a logic analyzer or SCSI analyzer to
resolve.

This may sound like it is hard to write your own
driver.  It is.  This may sound like we are trying
to scare you off from writing your own driver.  We are.

-- 
	Joel West  (c/o UCSD)
	Palomar Software, Inc., P.O. Box 2635, Vista, CA  92083
	{ucbvax,ihnp4}!sdcsvax!jww 	jww@sdcsvax.ucsd.edu
   or	ihnp4!crash!palomar!joel	joel@palomar.cts.com