Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!sdd.hp.com!elroy.jpl.nasa.gov!jarthur!nntp-server.caltech.edu!laguna.ccsf.caltech.edu!daveg From: daveg@near.cs.caltech.edu (Dave Gillespie) Newsgroups: comp.arch Subject: Re: 64 bits--why stop there? Message-ID: Date: 1 Sep 90 05:23:43 GMT References: <6106@vanuata.cs.glasgow.ac.uk> <2437@crdos1.crd.ge.COM> <631@array.UUCP> <225@csinc.UUCP> <1372@svin02.info.win.tue.nl> <41188@mips.mips.COM> <1990Aug31.174957.9612@cimage.com> Sender: news@laguna.ccsf.caltech.edu Organization: California Institute of Technology Lines: 44 In-Reply-To: paulh@cimage.com's message of 31 Aug 90 17:49:57 GMT >>>>> On 31 Aug 90 17:49:57 GMT, paulh@cimage.com (Paul Haas/1000000) said: > If bit addressing is "A Good Thing" aka. someone has a need for it, > they will add it to their compiler or cause their compiler vendor to > add it. For example, some people have a real need for 64 bit integers, > thus many C compilers support type "long long". I think John's original question was about using bit addressing across the board in hardware, which is a little different. You wouldn't need to add a bit-pointer type to the compiler, because all pointers would be bit-pointers. So the question is, can we switch to using bit-pointers without sacrificing performance, portability, low cost, etc. > Actually, I like the concept of bit-addressing. I just can't think > of a justification. I certainly wouldn't spend extra money on it > at this time. There's always the "pure research" justification. The extra cost is probably small, and there is promise for great benefits down the road, maybe even benefits none of us have foreseen. So it could be worth trying "just in case." Back when byte addressing was invented, it was probably a radical and dubious idea. After all, you can get along fine with word-pointers for most uses and byte-pointers for specifically byte-oriented work. Using byte-pointers for everything complicates the hardware, raises tricky issues like what to do about unaligned accesses, and so on. All you get for it is a pleasing internal consistency. Do you want to spend extra money on elegance? Now that we're used to byte addressing, the answer appears to be yes. In fact we take it for granted as one of the properties a serious modern architecture must have. Maybe years from now we'll all laugh (or curse) at those old clunkers that had different formats for bit- and byte-pointers. [Lest I become known as the net's great champion for bit-addressing, I think I should point out that I myself doubt it will ever really be "justified." I just think we should keep an open mind.] -- Dave -- Dave Gillespie 256-80 Caltech Pasadena CA USA 91125 daveg@csvax.cs.caltech.edu, ...!cit-vax!daveg