Re: Anyone running faster than 3 Mhz?

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

In article <D0tvHB.80r@utnetw.utoledo.edu>,
 <rsteinm@uoft02.utoledo.edu> wrote:
> 	A couple of days ago, I read a posting about buying 14Mhz 65816
> chips for around $20 a piece.  I was wondering what exactly that
> meant.  Was that for a complete drop-in processor (no other cards
> needed), or was that the price of a faster processor for the ZipGS
> system.

It is a faster processor for use in an accelerator.  You could put one
of these chips into the IIgs itself (assuming there is a 40-pin DIP
version; the ZIP uses a 44-pin PLCC version), but it would make zero
difference to the speed of the computer.

It is not possible to make the IIgs go faster without an accelerator
card.  The IIgs was designed to run at 2.8 MHz (and 1 MHz in "Normal"
mode) and cannot have its clock speed altered without replacing some
of the custom logic chips (particularly the FPI/CYA - the Fast
Processor Interface).  These chips are made by Apple, and they have
not and will not release a faster version.

With an accelerator, the processor on the card runs at a higher speed
than the rest of the computer, and caching is used to buffer
frequently accessed locations.  Internal operations by the computer
which don't require a memory access can also be executed faster.

Whenever the computer's memory or I/O is accessed (e.g. a read from a
memory location that isn't currently in the cache), the accelerator
slows down to the normal speed of the computer and performs a normal
memory access to the computer, via the adaptor cable plugged into the
processor socket.  This access will be at 2.8 MHz or 1 MHz, depending
on the location accessed, the speed setting, etc.

All write operations go to the computer as well as the cache, so they
cause the accelerator to slow down for one cycle.  All I/O reads
always come from the computer (and are at 1 MHz).

> 	By the way, for those of you out there with fast IIGS
> computers, what kind of investment is involved in accelerating the IIGS.

All you need to make the CPU go faster is an accelerator card.  There
are two options for the IIgs: the Transwarp GS from Applied
Engineering (out of business) and the ZIP GS from ZIP Technology.

The ZIP has several options: the cache size can be 8k, 16k, 32k or 64k
(larger caches and/or split code/data caches are possible with
modifications to the card, but I don't know the details).  The
processor speed can be anything from 7 MHz to 10 Mhz as supplied, and
can usually be upgraded to at least 12 MHz, 14 MHz in many cases, and
some people are claiming successful operation at 16 MHz.

Running faster than 10 MHz depends a lot on your computer - a noisy
machine is likely to have problems at high speed.  Going faster than
12 MHz requires a modification to the card (I don't know the details).

Regarding prices: I don't have any information handy.  I bought my
first ZIP GS (8 MHz/16k, later upgraded to 64k by ZIP Technology) in
late 1990, but it stopped working a couple of years ago.  I got
another one recently (second hand) which is currently 8 MHz/16k.  I'm
using it for a while until I'm satisfied that it works reliably
(certainly seems to) before I start trying to fix my old one and/or
upgrade the new one.


If you are currently running a floppy-based IIgs, you will also find
that a hard drive makes a big difference to the speed of the computer,
since the data transfer speed is so much higher.  (Not to mention the
benefit of having a lot more storage space online.)

Modern SCSI drives are much faster than models which are several years
old, and having a DMA-capable card (Apple High Speed or RamFAST) makes
a big difference.  The RamFAST is the fastest SCSI card, mainly due to
the cache RAM on the card.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand