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- Newsgroups: comp.lang.c++,comp.programming,comp.arch
- Path: uu4news.netcom.com!amc-gw!curtis
- From: curtis@amc.com (Curtis Green)
- Subject: Re: Why are 32 bit better than 16 bit pgms?
- Message-ID: <1996Feb8.212621.1658@amc.com>
- Organization: Applied Microsystems Corporation
- X-Newsreader: TIN [version 1.1 PL6]
- References: <1996Feb6.135808.12257@friend.kastle.com>
- Date: Thu, 8 Feb 1996 21:26:21 GMT
-
- Richard Krehbiel (rich@kastle.com) wrote:
- : curtis@amc.com (Curtis Green) wrote:
- :
- : >The "bits" quoted for the processor (16 bit, 32 bit, 64 bit, etc) is the
- : >size of the data path (data bus).
- :
- : [rest cut - I just want to gripe on this one point. :-) ]
- :
- : "Bitness" has become a marketing term, i.e. meaningless (rather like
- : the term "RISC"). There are a dozen different pieces inside a CPU
- : these days each with it's own bit width. Outside the chip there's the
- : data bus and address bus width. Inside the chip you have the general
-
- "Bitness" normally refers to the internal data path that the CPU core
- operates on. The best computers (and programs to run on it, as to the
- original posted question) are the one which the data bus size matches the
- "Bitness" of the CPU (8086 was better than the 8088, though they both had
- a 16 bit internal path).
-
- : register width, special register widths (i.e. Segment register = 16
- : bits, FP register = 80 bits), ALU width (multiplied by the number of
- : ALUs if superscalar), internal-cache-to-register path width(s), etc.
- : Then there's the architectural virtual address size versus actual
- : virtual address size versus the physical address size versus the
- : implemented MMUs capabilities. (Intel advertised that the 386 could
- : address 64 Terabytes - which is baloney. They added up 13 bits of
- : segment plus 32 bits of offset. They somehow forgot that this "45
- : bit" virtual address is then funnelled into a 32 bit paged MMU.) You
- : probably also have to consider what mode the OS software's running
- : too.
-
- The earlier postings were confusing the address width as being the "Bitness"
- of the processor. My point was that it tries to refer to size of data that
- the cpu can work with, not how many (bytes, words, longwords) of memory it can
- possibly access. Granted, it's become a marketing term. But since it is
- it is nice to know at least what is being talked about.
- :
- : What really matters is how fast it'll run what software. You might as
- : well forget making any generalizations based on bit size.
- :
- Sure, but if I go to computer land and ask for a computer that runs some
- software "realy fast", I need something to compare "realy fast" to. Knowing
- the bit size of the data the processor can handle can help me determine the
- reletive power of a computer (among other factors).
- : --
- : Richard Krehbiel, Kastle Systems, Arlington VA USA
- : rich@kastle.com (work) or richk@mnsinc.com (personal)
- :
-
- --
- Be seeing you...
-
- Curtis Green | Software Engineer
- curtis@amc.com | Applied Microsystems Embedded Systems
- | http://www.amc.com
- My opinions are |
- expressly mine | This year Khan escapes Earth on the Botany Bay.
- on my own. | (Cliff Clavin, 1996)
-