Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!gem.mps.ohio-state.edu!usc!snorkelwacker!bloom-beacon!eru!luth!sunic!mcsun!ukc!inmos!roger From: roger@wraxall.inmos.co.uk (Roger Shepherd) Newsgroups: comp.arch Subject: Re: parallel systems Message-ID: <2658@ganymede.inmos.co.uk> Date: 25 Oct 89 10:14:45 GMT References: <20764@usc.edu> <47279@bbn.COM> Sender: news@inmos.co.uk Reply-To: roger@inmos.co.uk (Roger Shepherd) Organization: INMOS Limited, Bristol, UK. Lines: 44 In article <47279@bbn.COM> slackey@BBN.COM (Stan Lackey) writes: >In article <20764@usc.edu> vorbrueg@bufo.usc.edu (Jan Vorbrueggen) writes: > >>Eugene, ever seen a transputer? Overhead for receiving or sending a >>message is 19 cycles (630 ns for a 30 MHz part). The actual transfer >>is done by a dedicated DMA machine at a maximum rate of 1.7 Mbyte/s >>unidirectional or 2.4 MByte/s bidirectional. > >1) Although it has high? peak bandwidth, the latency is still there. >The interconnect system waits for the processor to do an access, then >the processor waits for the interconnect to get the data. Many >microseconds go by between the time the CPU needs dependent data and >it is usable. > This is true BUT the time between a request being made and the data returning is NOT WASTED. It can be used to execute other processes. This use of `excess' parallelism is important precisely because it can hide latency. This is one reason why the transputer not only incorporates high performance communication links but also a hardware scheduler. The use of excess parallelism to hide latency is not new, it was used in the HEP. >Please recall that even the hypercubes (well inmos, ncube and thinking >machines anyway) do not use commodity microprocessors, but proprietary >ones that do the extras in hardware that they need > I'm not sure what you mean by commodity microprocessors. The Inmos transputers ARE commodity microprocessors, they are feely available to anyone who wants to buy them. The communication system which is provided with every transputer is there because it is generically useful in multiprocessor system (and you might be surprised just how many electronic systems are multiprocessor - my PC has at least 3 microprocessors in it (before I plug in my transputer card))! Roger Shepherd, INMOS Ltd JANET: roger@uk.co.inmos 1000 Aztec West UUCP: ukc!inmos!roger or uunet!inmos-c!roger Almondsbury INTERNET: roger@inmos.com +44 454 616616 ROW: roger@inmos.com OR roger@inmos.co.uk