Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!zaphod.mps.ohio-state.edu!samsung!uunet!brunix!rca From: rca@brunix (Ronald C.F. Antony) Newsgroups: comp.sys.next Subject: Re: Will the Next sell? (max memory size) Message-ID: <21954@brunix.UUCP> Date: 1 Dec 89 05:26:04 GMT References: <4283@helios.ee.lbl.gov> <21301@uflorida.cis.ufl.EDU> <21736@brunix.UUCP> <21795@brunix.UUCP> <21909@brunix.UUCP> Sender: news@brunix.UUCP Reply-To: rca@cslab7a.UUCP (Ronald C.F. Antony) Distribution: na Organization: Brown University Department of Computer Science Lines: 33 >Why is it unclear whether 64MB of memory is reasonable for use with a >68030? I'm not intimately familiar with the details of the >architecture, but it seems to me that this is more a function of the >operating system and the set of applications that are being run. The reason is the same as why cache speeds up a computer. According to the principle of locality (guess it is called like that in English, I try to translate it from German...) which was stated by von Neumann, a computer tends to work for a certain period of time in the same area of memory. Of course this area moves around in memory. If now the cache- memory or what we are talking about here, the disk-swapper can keep up with the supply of data, then there is not much speed lost with swapping. It is important, however, that the processor finds the data as often as possible in the cache/main-memory. (high hit rate!) This depends, if you are accessing data, which is not by nature in large parts sequential as are programs, on your algorithms. i.e. a merge sort on a huge ammount of data can do better than quicksort, because it accesses data in a pretty sequential way, and so makes the task for the swapper a lot easier. The speed of the processor comes into question, if we look at the speed with which this 'locality-window' moves around. A faster processor means a relatively slower disk, and therefore a heavier impact of swapping on performance. With more memory this can be brought to a new optimum. Ronald ------------------------------------------------------------------------------ "The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man." - Bernhard Shaw | rca@cs.brown.edu or antony@cogsci.bitnet