Re: New GS/new accelerator

[Frank Carney <frankcTAKETHISOUT@ANDTHISALSOsrv.net>]

Wayne Stewart wrote:
> 
> I'd agree with Supertimer that a 7mhz to 15mhz speed increase isn't by
> any means a small increase. I'd tend to think the effectiveness of higher
> speeds(100mhz) is going to be largely dependent on what the computers
> doing.For example viewing or converting a jpeg. Of course it'd help a lot
> almost everywhere if the accelerator has a good size cache.
> It would complicate things but I always thought a neat way to do it would
> be to have a cable running from the accellerator to the memory expansion
> slot, That way most of your memory'd be on the accellerator and be
> accessable at higher speeds.
> 
> Supertimer wrote:
> 
> > bobryan9@my-deja.com wrote:
> >
> > >Apple II accelerator (TWGS)
> > >can run at 16 Mhz if you're lucky
> > >boosting speed from 2.8 to 7Mhz seems like a big increase when you run
> > >programs
> > >boosting speed from 7Mhz to 15Mhz seems like a very small increase when
> > >you run programs
> >
> > Not entirely true.  Boosting speed from 2.8Mhz to 7Mhz
> > actually seems to have a very modest effect.  Boosting speed
> > from 7Mhz to 10Mhz will make things seem much smoother.
> > I have a 12.5Mhz TWGS and I can tell you that 12.5Mhz
> > seems to smooth things out A LOT compared to 10Mhz.
> > Only at 12.5Mhz do things actually seem snappy.
> >
> > Given the speed curve I've seen with increasing Mhz of the
> > CPU, I think that the 25Mhz is probably when you will
> > stop seeing much of an increase due to the bus (although
> > cached code will continue to increase in speed).
> >
> > >Apple II accelerators can have a 100Mhz processor, and still be hardly
> > >faster than a 15Mhz accelerator, because of the bottleneck of the 1Mhz
> > >bus and 1 Mhz video.
> >
> > Probably 25Mhz is where one would stop and figure it would
> > not be worth it to change speeds further.  This is my
> > extrapolation based on the differences I've seen while running
> > my TWGS at different speeds.
> >


Here is a serious question:
What does cache got to do with it?
Are we talking from experience in designing accelerators or is this just
an observation that existing accelerators go faster with a larger
cache?  I do not mean to be inflamatory, but I was hoping someone who
knows could explain the technical reasons behind a large cache. 
Besides, I just watched a rerun of "Whose Line Is It Anyway?".  It makes
me exagerate my true state of mind.