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more ?s about the xl3600

     Date: Thu, 10 Jan 91 13:36 EST
     From: Barry Margolin <intvax!barmar@Think.COM>
	 Date: Thu, 10 Jan 91 10:22:17 MST
	 From: drstrip@cs.sandia.gov (David R Strip )
	 In his description of the xl3600, peter paine writes:
	      The FPA option is a 125 Transputer hypercube coprocessor which can also
	      be used to run concurrent Lisp through shared memory.
	 I'm baffled ;-)
	 Why does a machine of this class have an FPA option. I would think it should be standard
	 equipment.                                   ^^^^^^
     It's already pretty fast without it.  You'd have to be pretty desperate
     to need to accelerate it even more.

Really? The posted spec said that the box contained 3 Ivory Mk.4 chips. The Ivories that
I have been familiar with used external FPAs (Weitek, I think). When was the FPA integrated
into the Ivory chip? Or is there a standard FPA in the xl3600 distinct from the 
optional Transputer one?
	 I'm even more baffled by how you configure 125 nodes as a hypercube.
     Sounds like a four-dimensional hyper-pentagonal-prism, with five nodes
     along each edge.
If that is true, then you only have a three-dimensional thing, which seems to limit
the amount of routing versatility. Seems like a strange choice of geometry, though
I haven't been following the area that closely. BTW, do you know what programming 
options there are for the hyper-thing, or is it done transparently in the compiler?