Aduke.2000 net.works utzoo!decvax!duke!bcw Thu Apr 8 22:51:09 1982 Re: Workstation power From: Bruce C. Wright @ Duke University Re: Workstation power Recently there has been quite a bit of discussion about computer system power as a function of MIPS. Although for some uses this is quite appropriate, it has been quite some time since most computing systems have been designed and purchased solely on the basis of MIPS. MIPS only give you the potential for CPU-bound tasks (and even then not very well, as I'll demonstrate later). For I/O-bound tasks (most data processing, database manipulation, editing, compilation, linking, word processing and so forth), a much more cogent measure can be I/O bandwidth. For example, recently here at the Medical Center where I work, we put together an LSI- 11/23 system with large (60MB) disk drives. We had to be rather careful which controller we purchased, because one of these high performance disk drives will simply saturate the poor Q-bus if there are long (multi-block) transfers. Since it wasn't really practical to modify the software to change multi-block requests into a series of single-block requests, we had to ensure that any controller we got for the system would automatically buffer the request in some way (say by breaking it up into smaller chunks and letting the drive spin around an extra time sometimes). The resulting system has about the CPU power of a PDP-11/34, but I can attest that it was *noticeably* slower for most types of computing, though we never made any performance measurements. Even for CPU speed, MIPS can be misleading without an understanding of the application and the hardware than such a vague number is able to give. For example, MIPS really don't have much meaning if the CPU doesn't have a floating point instruction set and you need to do a lot of floating-point math; ditto for decimal and to a somewhat lesser extent character instruction sets. Another example is interrupts: one of the fastest machines for large amounts of interrupt processing is the TI-990 series, since it takes only about 1-2 instruction times to enter an interrupt, save the registers and context, and be ready to begin processing the interrupt service routine. Try that on your PDP-11, VAX, or MC68000! The point is that this architecture was specially optimized for a highly interrupt-driven environment (such as process control) and it would take an enormous amount of hard- ware to make those other architectures run as quickly in that environment. MIPS only give the barest glimpse of the actual CPU speed; what really matters in questions of system speed is the total match of the system to the application. Even apart from simple performance criteria, there are a lot of other reasons why specific machines are chosen: software, for example. If you have specific software needs, you may have to forego the cheaper hardware in order to lower your total system costs. Back in the 1940's and early 1950's, it might have had some meaning to assign a single number to a computing system, but this technique no longer has any particular merit. Bruce C. Wright @ Duke University ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.