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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!spool.mu.edu!newspump.sol.net!www.nntp.primenet.com!nntp.primenet.com!feed1.news.erols.com!news From: Ken Bigelow <kbigelow@www.play-hookey.com> Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: freeBSD and P6/180 Date: Fri, 08 Nov 1996 19:01:57 +0000 Organization: Erol's Internet Services Lines: 124 Message-ID: <328383A5.1634@www.play-hookey.com> References: <32784DB5.2BDE@sybase.com> <3280D2FC.28D5@www.play-hookey.com> <57g22mmc2l.fsf@tees.elsevier.co.uk> <32823416.24F5@www.play-hookey.com> <55u0ci$fl5@nntp1.best.com> Reply-To: kbigelow@www.play-hookey.com NNTP-Posting-Host: kenjb05.play-hookey.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 3.0 (Win16; U) Matt Dillon wrote: > > :In article <32823416.24F5@www.play-hookey.com>, > :Ken Bigelow <kbigelow@www.play-hookey.com> wrote: > :>Paul Richards wrote: > :>> > :>> Ken Bigelow <kbigelow@www.play-hookey.com> writes: > :>> > :>> > > You don't want a cpu at that speed either, make sure it's a multiple > :>> > > of 33 1/3 (roughly). > :>> > > :>> > Now you've got me puzzled. What's wrong with a multiple of 40 or 50 MHz > :>> > (always assuming the motherboard can run at one or the other of thoses > :>> > speeds)? I would expect that a higher motherboard speed would be > :>> > desirable, too. > :>> > > :>> > Could it be that the motherboard is expected to clock at 60 MHz for the > :>> > PP180? That would make more sense to me than running a 30 MHz clock and > :>> > a 6X multiplier. > :>> > :>> Yes. But it sounds like you've got an out of date notion of bus > :>> speeds. 40 and 50 Mhz is *slow*, you want to run the bus at > :>> 66Mhz. Running the bus at 60Mhz is a 6Mhz drop which people don't > :>> think is significant until you point out it's 10% > :> > :>Obviously I'm more limited by my pocketbook than I had realized. My site > :>is still running on an ISA/VLB motherboard (486DX50) with EIDE drive, > :>etc. I can upgrade to a 5x86-133 (AMD) which overclocks to 160, but with > :>a 33.6K dialup connection, this is the bottleneck in any case. Ah, well, > :>when I win the lottery..... > :> > :>Thanks for waking me up, although it'll still be awhile. > :>-- > :>Ken > :> > :>Are you interested in | > :>byte-sized education | http://www.play-hookey.com > :>over the Internet? | > > The real significance is as much in bus WIDTH as it is in bus > SPEED. The PCI bus only runs at 33 MHz (I think), but at 32 bits wide > you get as much as 130 MBytes/sec out of it when doing > burst DMA or burst pipelined writes. Compare that to ISA, > where you would be lucky to get 5 MBytes/sec out of it. > > The dynamic rams used for memory are still the same old 70ns > SIMMs they have always been.. in fact, EDO is not fundamentally > different beyond the 'extended data out' portion... it's still > the same basic speed, just tuned such that a modern memory > controller can access it one clock faster. > > The difference is that on a pentium class machine two SIMMs > are accessed in parallel.. 64 bits rather then 32, doubling > the effective throughput. If you add interleaving (with > four SIMMs), you double it again. > > CPU caches are now a whole lot larger and a whole lot wider.. > A typical instruction cache is 128 to 256 bits wide. > Something like the pentium (pro) gets 200 MIPS (200 MILLION > instructions per second) by accessing a slower, but very > much wider cache subsystem. RISC chips generally work the > same way. Instruction execution is effectively decoupled > from the memory and, except for reads, the I/O subsystem, > allowing instructions to be executed at 10 times the rate > the nominal memory subsystem would otherwise be able to support. > > On the other hand, most RISC processors, including the > pentium come back down to earth with certain types of > non-cacheable or badly-cachable accesses. For example, > a read-modify-write in a video frame buffer is usually > non-cacheable and may be eight times slower then a simple > write to the same video frame buffer (which can be pipelined > and not have to stall the instruction stream). Many RISC > processors go to great lengths to avoid these bottlenecks. > For example, the pentium employs a branch-prediction cache > in an attempt to keep the instruction pipeline full even > through branches, calls, and jumps. A single cache miss is > roughly equivalent to 20 or more cache-hit instructions. > > Another example would be a pentium class machine trying > to read or write to an ISA card... icky! Or a pentium class > machine trying to do PIO (progammed I/O), which effectively turns > a pentium pro 200 into a 486 or worse. As long as you > have the cycles to burn, I guess it doesn't matter, but > if you need those cpu cycles, PCI cards and drivers that > support PCI DMA are required. > > Microcontrollers also take quick advantage of caching as well. > You can now purchase a $30 single-chip RISC microcontroller > capable of 20+ MIPS using the SAME memory subsystem as an > older non-cached cpu (e.g. 68302) which accesses memory for > every instruction and runs along at a whopping 2 MIPS. Amoung > other things, this makes coprocessors extremely cheap, in > order to allow the main cpu(s) to NOT have to spin expensive > cycles on external accesses. > > -Matt Wow! I hadn't expected a lengthy discussion like this as a response. Actually, the basic "hole" in my own experience is the PCI bus. I've done at least some work with SCSI, although not at home. The RAM I'm using is actually 60 ns rather than 70 (16 MB SIMMs), and the main server motherboard is running at a full 50 MHz. If/when I jump to the AMD 5x86, the processor will speed up but the motherboard will slow down to 40 MHz. Either way, until I can afford at least an ISDN connection, I think the modem will still be my primary bottleneck. Anyone know the next set of winning Powerball numbers?? I am using the VL Bus for my I/O, so at least *that* isn't limited to an 8MHz ceiling and 16 bits. But a 33.6K modem doesn't exactly soar with the eagles. I'm still dreaming about some heavy hardware upgrades, although I'll be looking for speed rather than computing power -- how much actual computing power is needed by a Web server/gateway/etc. which won't be used as a workstation, after all? I just always seem to find more urgent places to spend the money.... -- Ken Are you interested in | byte-sized education | http://www.play-hookey.com over the Internet? |