Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/3/84; site talcott.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!panda!talcott!tmb From: tmb@talcott.UUCP (Thomas M. Breuel) Newsgroups: net.micro.68k Subject: Re: Re: 32 vs. 24 Bit Addresses Message-ID: <319@talcott.UUCP> Date: Sun, 3-Mar-85 18:45:33 EST Article-I.D.: talcott.319 Posted: Sun Mar 3 18:45:33 1985 Date-Received: Tue, 5-Mar-85 01:46:17 EST References: <342@oakhill.UUCP> <429@bonnie.UUCP> Organization: Harvard University Lines: 18 > Of course, hardware upward compatibility doesn't guarantee software > compatibility. A number of 32-bit processors have been crippled by > operating systems writers who, when they designed their software, > saw only physical hardware with 16mb or less and said "we only need > 24 bits". Typically the upper byte is used for the number of arguments > or argument words. Well, the argument is not "we only need 24 bits". The argument goes more like "if we use 32 bit pointers, then we need at least an extra word for type/number of argument information, and at least an extra memory access per operation. This means that our software will use at least 33% more memory and time than other people's software". If you are careful, btw, you can write your programs (in, say, 'C') in such a manner that implementation details like this don't make the code unportable. Thomas.