Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!mips!hal!mark
From: mark@mips.COM (Mark G. Johnson)
Newsgroups: comp.arch
Subject: Re: Futurebus+ @ 500MBytes/sec
Message-ID: <33845@mips.mips.COM>
Date: 19 Dec 89 15:31:53 GMT
References: <276@leia.WV.TEK.COM>
Sender: news@mips.COM
Reply-To: mark@mips.COM (Mark G. Johnson)
Organization: MIPS Computer Systems, Inc.
Lines: 38

In article <276@leia.WV.TEK.COM> johnt@opus.WV.TEK.COM (John Theus) writes:
  >
  >As I stated in a previous posting, we expect to be building Futurebus+
  >hardware in the coming year that can sustain 500 Mbytes/sec on a 64 bit
  >wide data path.  The questions that immediately come to mind are either
  >this does meet your definition for "fast", or you don't believe we can
  >deliver this bandwidth.

Could you explain what is meant by "sustain" above?  At least two
really cool things might be implied by this:

  (1)  In the coming year you'll be building Futurebus+ hardware that
       can transfer 512 bytes (i.e. 128 words, or 64 bus-widths of data)
       in 1024 nanoseconds.  This'd be a cache refill from main memory.

  (2)  In the coming year you'll be building Futurebus+ hardware that
       can do a DMA transfer of 50 Megabytes in 0.1 second.

Are either of the assertions above correct?  {they're based on the assumption
that (500 MB/sec  /  8 bytes/transfer) = 62.5 Mtransfers/sec = 16ns/transfer
is the bus cycle time in "sustained" operation}


Also, folks might think it was a bit smelly to claim high throughput rates
for a "bus" that only has two or three slots, or for a "bus" that doesn't
involve a printed circuit backplane board having connectors or sockets for
separate daughterboards.  Just to lay these types of silly "oh-yeah?"
questions to rest permanently,

   Does next-years-500MB/sec-Futurebus+ have a mother/daughterboard
   construction with N>6 connectors and card slots, and will it run
   at 500 MBytes/sec when fully populated?

Thanks.
-- 
 -- Mark Johnson	
 	MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086
	(408) 991-0208    mark@mips.com  {or ...!decwrl!mips!mark}