Second Hard Drive for UNIX-pc; HwNote10

[Dave Ihnat]

In article <420 at limbic.UUCP> gil at limbic.UUCP (Gil Kloepfer Jr.) writes:
> [My input]
>There are **VERY** good ones for keeping them on the same upgrade.  I will
>start with those, since they answer many of your reasons:
>
>	1.  The *only* real thing that the P5.1 upgrade performs
>	    is the creation of the MCR2 register (physical I/O port)
>	    which is used for a 4th head select bit, the second hard
>	    drive select bit, and the signal to the OS that P5.1 is
>	    installed.

But, if somebody's ALREADY installed this upgrade--as I have--youre upgrade,
unless you do some arm-waving to make it compatible, is unusable to me.  And
some hundreds--or thousands?--of other upgraded machines.  And yes, I did the
upgrade myself, from information released by Convergent...

>	2.  Because of (1), having two separate upgrades means extra
>	    circuitry to decode the address bits which ultimately
>	    define the same port.  Highly unnecessary.

Again, unless you consider the multiple-upgrade problem.  Also, this extra
circuitry is, I believe, very minimal...

>	3.  The simplicity of the second hard disk upgrade, minus
>	    a lifted pin (can be left out if you never use the
>	    second hard disk upgrade) is just as easy as the P5.1
>	    upgrade.

Ok, how does that work with P5.1 upgraded units?

>To bring up an even more elementary point, the only reason why you'd want to
>upgrade to P5.1 in the first place is for a 4th head select (for a big
>disk drive) and/or the 2nd drive select.  You might as well kill two birds
>with one stone than to keep opening the machine and fiddling with upgrades.

It's already been done to the machine I'm worried about.  Does your upgrade
allow for such units?

>>1) Existing upgraded units.
>>   A combined upgrade either would be unavailable to these units
>
>This doesn't make too much sense in my book.  Are you talking about these
>public-domain (sort of ;-) upgrades or commercial ones?  If the latter,
>don't worry about it...there won't be.

Oh, come now.  OF COURSE there won't be any commercial ones!  And yes, as I've
belabored up to now, the information for the larger disk upgrade has been
available for quite some time, and I'm aware of many machines that are modified
(successfully) to use this upgrade, including mine.  Your comment here is a
no-op; included for amusement, but sidesteps an important issue.

>Furthermore, it means that you have to consider which upgrade will provide
>the bit for P5.1.  Then you will end up having to install both if you
>want to use the upgrade that doesn't do P5.1.  I believe you need P5.1
>in order to use the second hard disk select bit.

Ok. You have to install both.  The P5.1 upgrade was so easy I coached a guy
through it who had to practice on solder technique first...

>>3) Cost
>>   The cost of the combined upgrade will be greater than a single upgrade
>
>Minimally.  The extra chips/sockets necessary for the second hard disk
>will cost another $5-$8, depending on source.

Yah, OK.  This was, I believe, low on my list.  (On the other hand, when I
was in school, $8 would buy 5 pitchers and two spare beers...)

>As it currently sits, the P5.1 upgrade with 4th head select requires a PAL
>which is not necessarily available to most folks (I had someone do it for
>me as a favor).  The combined upgrade I proposed (and mentioned the $50
>price) was that at absolute maximum to save my own neck should it be more
>for someone else.  I *know* it can be done for a lot less than $50, and
>even less for someone who has a good stock of chips available (I do a lot
>of tinkering as a hobby, and keep a lot of chips around).

Well, if they're a tinkerer and have a lot of chips, then a PAL isn't too hard,
either.  If they're not, then both are problems.  Still, I think that the fact
that so many P5.1 upgrades have been done makes consideration important...

>I already mentioned how it works at the beginning.  The aesthetic problem is
>only in getting the wires from the cabinet.  If you don't use the 2nd drive
>select, then you never plug the cable into the jack on the perfboard, it's
>as simple as that.  In effect, you are getting more for your money, and
>doing less to your motherboard over a period of time.

No, I meant keeping upgrades separate.  One has already been 'released';
keeping the two separate both isolates the purposes of the upgrade--larger
disks, and more disks--and remains downward compatible.  Some people may never
be able to, nor care to, afford 80 Mb disks, but can get two 20 Mb drives free.

>Inasfar as motherboard work goes -- I would feel a lot more comfortable
>messing with my motherboard ONCE and leaving it alone, rather than connecting
>wires to it TWICE and increasing the chance for costly damage.

Alternate opinion--mess with it once, and if it then works, you know THAT work
is reliable and functional when/if the next modification doesn't work.  Or,
you have test equipment for a motherboard when twice the number of chip and
wiring mods go bad?

>I appreciate your opinion, but I don't feel that it is as substantial as
>it appears on the outside.

Well, I really do.  Especially as--as you may have guessed--I have one of those
upgraded units which won't be able to use your upgrade...

>Again, the two upgrades are closely related,
>and they're almost meant to be done together.  I already have someone
>who wants to work on a PAL design which will likely eliminate 4 TTL ICs and
>could fit right on the motherboard like the current P5.1/4th-head
>upgrade

Well, you just included a custom PAL anyway--how about one which works in
place of the P5.1 upgrade, or serves the same needs as both?   Yes, they're
related, but I think that unless you answer the problem of already-upgraded
units, you're gonna get bad PR for this upgrade, despite the (appreciated!)
effort you're putting into it.

>(although I would prefer to see the PAL on a separate piece of
>perfboard with the appropriate disk driver chips, like John probably does).

Why?  There are empty pads on the motherboard for the P5.1 upgrade that work
marvelously; what's wrong with using them, if you already have to pull the MB
and solder on it?

>BTW: The combined upgrade now is a total of 6 chips, and about
>thirty inter-chip connections [Vcc/GND included].  There are 14 connections
>to the motherboard, which includes the power supply for the chips.  Seven
>of the motherboard connections are required for the P5.1/4th-head upgrade.
>Hope this helps to clarify things a little.

Well, yes--but actually, it reinforces my feeling that two separate, less
complicated upgrade steps are much preferable to one comprehensive, complicated
upgrade.  Many people applying this will be inexperienced with hardware hacking
(as with one fellow I coached through the P5.1 upgrade), and it'll make their
(or my) job easier to debug a two-step upgrade.

	-Dave Ihnat
	 Analysts International Corp.