>: Thanks for replying to a message without understanding what it was
>: about. We were discussing why certain *motherboards* are built they
>: way they are, and I pointed out that a motherboard built to run at
>: 50 MHz (486DX-50) has to be better (higher quality) than one built to
>: run at 33 MHz (486DX-33 or 486DX2-66). The computer with the
>: 486DX2-66 might have a higher performance, but it is irrelevant.
>When the DX50 was first released many questionable vendors immediately
>dropped them into there so called DX/33 system boards. And actually,
>this worked great. No modifications were needed and the system boards were
>already available and ready to go...
The peripheral chips (chipsets) like DMA controller, interrupt controllers,
DRAM controllers also have speed ratings - just like CPUs and memory chips.
Do you waste money on 70 ns DRAM when 100 ns is cheaper, just because the
specs call for it? Some chipsets are rated by their manufacturer for less
than 50 MHz processors. If you run it faster, you push the margins. This
is compounded by the fact that higher frequences make the motherboard design
trickers - stray capacitance or signal coupling problems get worse (this is
very much RF design, being in the low range of broadcast TV!).
When you push the margins, sometimes it will work and sometimes it will not.
When the supply voltage drifts up or down a tad, or the temperature
changes, or the cards you put in change the capacitance, or even the
components age - sometimes it may flake out on you. This varies from
motherboard design to motherboard design, chipset to chipset, and even
between supposedly identical motherboards. If it works for you to clock
a 486DX40 at 50, great. But that doesn't mean that it will be reliable
for everybody. Likewise 33 MHz motherboards clocked at 50 MHz, even with
a true 50 MHz CPU.
Quote:>The point is that almost any i486 system board that is rated at 33Mhz
>-AND- has BIOS support for 50Mhz can run at 50Mhz indefinitely. Even if
>the BIOS doesnt support 50Mhz it only means that you are loosing some
>clock cycles somewhere. You will still see an
>improved performance *AND* the board should be able to maintain that
>speed for the expected MTBF for that product.
The BIOS is mostly irrelevant. One can run 50 MHz with a BIOS that has
no idea what the speed is, or plug a BIOS that has some speed options into
a motherboard that can't handle 50 MHz. One does NOT lose some clock cycles
here and there like spilled gasoline from a bad fuel line; if you "lose" a
clock cycle, you just corrupted your data and things are going to go bad in
a way you won't like.
The MTBF or lifetime of the motherboard could conceivably be a concern only
if the chipset was overheating. This is not typically the problem. The
problem is occassional unreliability. Unexplained hangups or bus errors.
When you over-do it, sometimes you will get by with it, sometimes not. It's
fine for people to try to push the clocks, but they should know the true
tradeoffs, and not be misled about the nature of the risks. If you want to
run an old motherboard faster than it's rated, check the chip temperatures,
carefully. Unless they are very hot, your only risk is unreliability.
Z
Quote:>: A 486DX2-100 (50 MHz MB) would have a higher performance than a
>: 486DX3-100 (33 MHz MB), but would require a higher quality (more
>: expensive) motherboard.
>Yes a DX2/100 would have better preformance than a DX3/100 simply because
>the system board is running 51.51% faster than the DX3 counter part.
>But it would not necessarily mean that a 'superior' system board is
>needed to accomodate these speeds.
>--
><>--------------------------------------------------------------------------<>
><> <>
><> Following his arrest, it was estimated that his little scam netted him <>
><> $6,000 that year. He is on probation, his equipment confiscated, but if <>
><> you asked him why he hacked he still sighs: "It's the greatest thing in <>
><> the world man." <>
><> <>
><> (>---> Approaching Zero <>
><> <>
><>--------------------------------------------------------------------------<>
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