Re: Number Cruncher FPUs

[Michael Kennett <kennett@math.ubc.ca>]

Dirk Froehling wrote:
> 
> In article <4occtk$bb7@iggy.apana.org.au>, posty@triode.apana.org.au
> (Andrew Roughan) wrote:
> 
> >I'm considering buying a Number Cruncher, and am wondering
> >whether the Motorola 68882 FPU, 25MHz, PGA package
> >is suitable for it?
> 
> I currently don't recall what PGA stands for. Is this the ceramic package?
> If so, it will work.
> 

The PGA stands for "Pin Grid Array". It is a layout of the pins of the
silicon chip package.  Typically, PGA packages have a large number of pins
~ 168 is not uncommon.  The pins are all on the underside of the chip.

PGA's are more modern than the `DIP' (Dual Inline Package) chips. DIP's
are rectangular, typically black, and have two parallel rows of pins
sticking out from the sides of the package. You don't usually see DIPS
having more than 40 pins, but before PGA's came out, there were some big
DIPS - I've seen a 64-pin DIP.

All of the chips on the Apple ][+ motherboard are DIPS.

The larger chip packages are typically ceramic, rather than plastic.
This has to do with the dissipation of heat away from the silicon substrate.
All of the PGA packages that I've seen are ceramic.


Mike Kennett
(kennett@math.ubc.ca)