Xref: utzoo alt.folklore.computers:7707 comp.unix.internals:1239 comp.misc:10751 Path: utzoo!utgpu!cs.utexas.edu!sdd.hp.com!uakari.primate.wisc.edu!abcfd20.larc.nasa.gov!ipsun.larc.nasa.gov!jcburt From: jcburt@ipsun.larc.nasa.gov (John Burton) Newsgroups: alt.folklore.computers,comp.unix.internals,comp.misc Subject: Re: Jargon file v2.1.5 28 NOV 1990 -- part 5 of 6 Message-ID: <1990Dec5.144445.18632@abcfd20.larc.nasa.gov> Date: 5 Dec 90 14:44:45 GMT References: Sender: news@abcfd20.larc.nasa.gov (USENET File Owner) Organization: NASA Langley Research Center, Hampton, VA USA Lines: 44 In article pcg@cs.aber.ac.uk (Piercarlo Grandi) writes: [...] >pst> You're comparing CPU performance to I/O performance. [ ... ] Back >pst> when there were REAL(tm) computers like 780, a lot of time and >pst> energy went into designing efficient I/O from the CPU bus to the >pst> electrons going to the disk or tty. [ ... ] Sure OS's and apps have >pst> gotten bloated, but when you put a chip like the MIPS R3000 on a >pst> machine barely more advanced than an IBM-AT you end up with a toy >pst> that can think fast but can't do anything. > >No, no, no, no, no, no, no. The IO bandwidth of a typical 386 is >equivalent or better than that of any UNIBUS based machine, and, in >practical terms, equivalent to that of MASSBUS based ones. You can get >observable raw disc data rates of 600-900KB/s and observable filesystem >bandwidths of 300-500KB/s under SVR3.2 (with suitable controllers and a >FFS of some sort). This is way better than a PDP-11. > True, a typical 386 machine has good I/O bandwidth, but bandwidth isn't everything. The majority of 386 machines have an ISA bus which is a very simple bus controlled by the cpu. When performing I/O, the cpu blocks itself and turns control of the bus to the I/O device. When the I/O operation is complete, control returns to the cpu, which unblocks itself. What this means is that any I/O severly impacts the apparent system response. As a single user system, the typical 386 machine is just fine. A typical multi-user, virtual memory system (UNIX) requires a significantly greater amount of I/O than a single user system. Machines that were originally designed as a multi-user platform usually where set up so that the I/O could be performed without the direct control (or blocking) of the cpu. The system bus was designed so that multiple operations could occur more or less independent of the cpu (multi-tasking hardware design). The typical 386 machine is designed as a single tasking machine (regardless of what the cpu can do, the bus & support hardware was designed for single tasking). If you are planning on using a 386 machine as a multi-user platform, you might want to consider an EISA or an MicroChannel based system as opposed to an ISA based system. EISA & MicroChannel at least have some provisions for multi-tasking operations. Hope this helps some. John Burton Brought to you by Super Global Mega Corp .com