Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!tut.cis.ohio-state.edu!sei.cmu.edu!firth From: firth@sei.cmu.edu (Robert Firth) Newsgroups: comp.arch Subject: Re: Segmented Architectures ( formerly Re: 48-bit computers) Message-ID: <23189@as0c.sei.cmu.edu> Date: 26 Mar 91 15:00:22 GMT References: <1991Mar21.164242.886@sj.nec.com> Reply-To: firth@sei.cmu.edu (Robert Firth) Organization: Software Engineering Institute, Pittsburgh, PA Lines: 33 In article efeustel@prime.com (Ed Feustel) writes: >The major difficulty with a segmented architecture in today's marketplace >arises from the use of the language C and C's notion of a pointer as the >total address. No. The major difficulty with a segmented architecture is that it's wrong, and the von-Neumann model is right. This is not a language issue. One of the most fundamental, and most pervasive, idioms in practical computing is the mapping function whose domain is a subset of the natural numbers, in other words array (0..max) of Object This has been true of every language since before Formula Translation I, and will remain true for as long as we have integers and like to count. Yes, the set of integers is dense and monotonically increasing, and hence so will be the set of array indices, and hence, on the natural memory model, so will be the set of object addresses. Don't blame C - as Kroneker said, God made the natural numbers. >If you are saddled with small segments with N < 2**18 or so, you will soon >come to hate segments because you have to continually map C addresses onto >multiple segments in order to support the linear model. With N ~ 2**32 >this is much less of a problem since the need for individual objects of this >size is much reduced. The size of the segment is not the point. The point is that the physical memory is capable of holding an array of a certain size, but the addressing scheme won't let you index it. You have only to hit this problem once in a lifetime, to vow never again to buy a machine with a segmented address structure.