Re: ZIP-GS ACCELERATOR: Questions

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <D7rCsq.Cqn@presby.edu>, Stephen Buggie <sebugg@presby.edu> wrote:
> 
> QUESTIONS:
> 
> 
> 1.   Is ZIP still in business?  I heard rumors that they quit.

Yes, they are still in business.  They changed their name.  They are
now called "MCTA, Inc.", or something like that.

>      Is the ZIP-GS still in production?   Will a factory warranty be
>      available on ZIP-GS?

Almost certainly.  People are still buying ZIP GS's from MCTA (at
least, they've been asking about the address, and I haven't seen
anyone saying they were unable to get one).

On the other hand, the ZIP CHIP (for 8-bit machines) is out of production.

> 2.  What is the difference between the 16K cache and the 32K cache?
>     Do you just add RAM chips to increase the cache?  How do they
>     perform differently?

Yes, you can add RAM chips to incrase the cache size, but this has to
be done carefully - you need reasonably high speed static RAM on an
accelerator.

The advantage of having a larger cache is that the ZIP will be able to
spend more time running at its maximum speed.

A quick summary of how the card works is in order:

Whenever the CPU on the ZIP wants to read a byte from memory, the ZIP
checks to see if that location is in the cache.  If it is, the byte
will be read from the cache at the maximum speed (e.g. 8 MHz for an 8
MHz ZIP).

If the location is not in the cache, the ZIP must resynchronize with
the IIgs motherboard and perform a normal memory access (at 2.5 MHz or
1 MHz).  The byte is then stored in the cache and delivered to the CPU.

If the same location is read again, it will be read from the cache
rather than from memory.  For example, a program loop will run slowly
the first time (as it is read into the cache) and will then run at
maximum speed.

If the cache is full, a location that hasn't been accessed recently is
thrown out to make room for the new one.

The larger the cache, the more locations can be cached before older
ones must be discarded.  As a result, the ZIP is running at full speed
more of the time, when executing reasonably scattered code.


The above description is somewhat simplified, but it covers the basic
principles.

A faster CPU on the ZIP will generally result in a more noticeable
speed improvement than an increase in the cache size.

> 3.  Is the 8MZ version highly reliable?

Yes, usually.

I'm on my second ZIP.  I bought the first one (8 MHz/64k) in 1990.  It
worked fine for at least a year, then started to get flakey (random
crashes, memory corruption, etc.) I eventually removed it from the
computer.  Later on I bought a ROM 3, and reinstalled the ZIP in
there.  It worked fine for several months, then started misbehaving
again.  It got so bad that I have removed it permanently. 

This is not a common situation - I haven't heard of anyone else having
problems like this.  A friend of mine bought a ZIP at the same time,
and his has been working perfectly.

The second ZIP (8 MHz/16k) has been going fine since it was first
purchased in 1991, through two machines.

> 4.  How COMPATIBLE is it with other IIGS items?

Very.  If there are some hardware items and/or software that doesn't
work properly at accelerated speeds, you can configure the ZIP to slow
down as required (e.g. on a slot access), or you can just disable it
when running incompatible hardware/software.

It ocassionally has hardware compatibility problems, generally with
devices that are already breaking Apple's loading/driving rules for
the slot.  The only example I'm aware of is the PC Transporter.  Early
PC Transporters used with early ZIPs do not work properly.  A
modification can be made to the ZIP to get it to work.

> 5.
> Is it compatible with the RAMFAST scsi card (am considering getting one.)

Yes.  What is more, it is compatible with the RAMFast's trick of
supporting DMA to memory cards larger than 4 MB (unlike the TransWarp GS).

Note: the ZIP GS is smaller and much less power hungry than the
TransWarp GS.

> I have installed 8 but 8 MHZ ZIP chips in two of my apples
> so I am experienced with chip insertion.

The ZIP GS is a card, like the TransWarp GS, with a jumper cable that
runs to the CPU socket.

> 6.  What sellers have ZIP-GS?   (I have a quote from one seller of
> $189 for the 8 MHz/16K cache model)

That is about the usual price (GS+ quotes exactly this price).

> 6.  CPU CHIP model vs. Interface Card model:  In the Fen 1991 issue of
> Incoder/A+ there is an ad showing two versions:  A CPU Chip model (actually
> a tiny card that plugs into the CPU socket) and a full sized interface
> card.  Which model is preferred?

The "card in the CPU socket" models were never released.  The only
available version is the full slot-based card (originally called the
"ZIP GSX").
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand