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I'm building a 486 computer. I plan on using a 100 MHz 486-DX4 that I have which I believe is about as fast as 486's went.

The motherboard I will use (Socket 3) appears to support putting a heatsink and fan over the CPU but I'm not sure if it is needed. The main PSU is already loud so I'd rather not use a fan/heatsink for the CPU if I don't have to. Although, since they don't make 486's any more I might want to reconsider.

So, is a heatsink/fan required for 486's or is it just recommended? I don't plan on over-clocking but at 100 MHz the heat might climb quite a bit.

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    If you use a larger heatsink, it can be quieter as you can skip a fan. For a PSU, you might be able to rewire a modern, quiet one for older boards. – Nick T Aug 16 '17 at 21:28
  • If the PSU fan is loud it's not hard to replace (I'm not particularly handy but I managed it). What you don't want is the fan dying particularly if you don't have a fan on the CPU -- and if it's making noise you may want to be proactive and replace it. – David Aug 16 '17 at 21:41
  • You may want to look into Pentium Overdrives if you want to go all in. That will probably allow you to run Quake. – Thorbjørn Ravn Andersen Aug 16 '17 at 22:37
  • No matter if back then it would have required a heatsink, these days you should definitely use one for the reason that it extends the silicons lifetime; 486s aren't produced in large numbers anymore. – PlasmaHH Aug 17 '17 at 8:45
  • Ye old trick to reduce fan noise is to go bigger and slower, simply get some big chassis fans (120mm?) and wire them to 5v instead of 12v (or get fan speed thing), not only cpu life is prolonged by good heat management. – PTwr Aug 17 '17 at 11:57
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It depends on the airflow in your computer. You can run even a 100 MHz 486DX4 without a heatsink or fan, if your PSU’s fan (or another fan) pulls enough air over it; they commonly used heatsinks though (without fans). You can find examples of pretty much all configurations starting with the DX2/66 (or even the DX/50, but that’s pretty rare): no heatsink, heatsink only, heatsink and fan.

Even some Pentiums can run without a fan — I have a 166 MHz Pentium running fine with only a heatsink. (Early 60 MHz and 66 MHz Pentiums did need a fan though, they ran much hotter.)

The airflow requirements vary depending on the specific processor you use. The Intel manuals give some figures:

  • the 100 MHz DX4 can cope with an ambient temperature (inside the case) of 29°C if the airflow over it is at least 200 ft/min, without a heatsink, or 35.5°C with no forced airflow with a heatsink (see p. 2-353);
  • the 66 MHz DX2 can cope with an ambient temperature of 28.3°C if the airflow over it is at least 600 ft/min, without a heatsink, or 40.9°C if the airflow over it is at least 200 ft/min, with a heatsink (see p. 15-3);
  • the 33 MHz DX can cope with 27°C if the airflow over it is at least 200 ft/min, without a heatsink, and 31°C with no airflow with a heatsink (see p. 169, 171 in the PDF).

DX4 CPUs use 3.3V instead of 5V so they run cooler than you’d expect. There are low-voltage variants of 486 CPUs which would run cooler still.

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    60 and 66MHz ran on +5 volt, later ones one +3.3v volt. That is a lot of extra power to dissipate. – Hennes Aug 16 '17 at 23:14
  • I can confirm. The fastest CPU I had that ran heat-sink only without fan was a Cyrix 5x86-100 (basically a faster 486-class chip). I've also seen CPUs in that same ballpark equipped with a fan clipped directly to the CPU with no heatsink. – mnem Aug 17 '17 at 2:02
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    Here's the i486 processor manual, and the before-before-last page of it gives the package thermal specifications. – Iwillnotexist Idonotexist Aug 17 '17 at 6:51
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    @mnem "Cyrix 5x86-100 (basically a faster 486-class chip)" Well, not realy. unlike the AMD 5x86, which as just a faster clocked (x4) 486, the Cyrix 5x86 was a apentium alike chip scaled down to work with the 32 Bit 486 bus. While some Pentium ISA extension where disabled to save circuity, it did leave several Pentium opcodes/functions enabled thus offering an enhanced architecture. Being a hybrid, it outperformed all other Socket 3 CPUs, including the Intel Pentium Overdrive (PODP5V83), as they only offered 83 MHz maximum clock. The mid 90s where a great time for competive CPU manufacturers. – Raffzahn Aug 17 '17 at 10:06
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    Ahhh, important fact to remember: 486 era class computers commonly did not have any automatic fan control for the main power supply fan, so the fan could be relied on going full blast. – rackandboneman Aug 18 '17 at 21:24
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You should at least use a heatsink. For slower CPUs (like yours) it will work without a fan - if the heatsink is large (large for 1995 standards).

A 100 MHz DX2 (50 MHz FSB, multiplier of 2) is a pretty rare beast - as 50 MHz boards are - since neither Intel nor AMD ever sold them (officially). Are you sure you're not using a 486DX4 with a 33 MHz FSB and a multiplier of 3?

The fastest 486 officially available was the Am486DX5 with 150 MHz (50MHz x 3) or 160MHz (40 MHz x 4). AMD also sold them as Am5x86, but they were just 486s without any changes except the clock frequency. I've got one with 133 MHz (33x4) still running as a game server.

With appropriate cooling the 160 MHz could also run on 50 MHz FSB boards resulting in a 200 MHz 486.

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    I may have my numbers a little off. I own a DX4-100 that I eventually plan to use. I also just bought a DX2-50 CPU/motherboard but I haven't received it yet. Is that rare? – cbmeeks Aug 16 '17 at 18:28
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    I think the DX50 — i.e. 50Mhz bus, no clock doubling — is rare, because it was often problematic with VLB cards in practice and the DX2s came out only a year later with no such problems. Though I feel anecdotally like the DX2-66 was the big seller, so the DX2-50 might well also be a rare thing. – Tommy Aug 17 '17 at 1:17
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    @Tommy That's exactly correct. Because the VLB bus runs at the same speed as the CPU clock, and many VLB cards couldn't handle more than a 40MHz clock, DX-50 CPUs were pretty rare. You basically had to hunt around high and low to find VLB cards that wouldn't fall over at 50MHz. DX2-50s aren't particularly rare though, they were used in a lot of budget computers, since the 25MHz bus rate mean you could use less expensive components with it. DX2-66s were definitely very common though. – mnem Aug 17 '17 at 1:55
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    "For slower CPUs" It's not about speed. Slower CPUs can use less power than faster CPUs, this is way too much of a blanket statement to be useful and it's actually putting people on the wrong path. – Mast Aug 17 '17 at 9:23
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    @Raffzahn even just considering 486s, power consumption didn’t necessarily scale with CPU speed — there were low-power variants, and behaviour varied depending on the manufacturer. Additionally, DX4s ran on 3.3V instead of 5V, which helped reduce their energy consumption. – Stephen Kitt Aug 17 '17 at 10:51
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Practice with actual 486-era PCs was:

The non-clock doubled, sub-40MHz types (the original 486DX 20/25/33MHz) usually were neither heatsinked nor equipped with a fan.

When the 50MHz (non clock doubled DX type, do not confuse with the 25MHz FSB DX2/50!) came on the market it was plagued by heat problems, and either fanned or peltier-assisted spot-cooling devices quickly entered both PC production and the catalog of DIY parts stockists.

Heatsinking single ICs had been a well known practice both with non-PC workstation CPUs and other high performance ICs in professional electronics at that time.

Once the PC world had familiarized itself with spot coolers (which at least at that time was the engineering term often used to describe "active" heatsinks), they stayed; by the time the DX2 types (even though some of them were less of a thermal nightmare) became popular, fanned heatsinks were a commodity item and often integrated into new systems by default.

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    Well, even these days CPUs are sold without a heatsink and fan, but a completely and correctly built DX2 computer without sounds unusual... – rackandboneman Aug 17 '17 at 9:41
  • Edited in some required vagueness. – rackandboneman Aug 17 '17 at 10:44
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    I've totally seen OEM built DX2-50s in the wild with no factory installed heat-sink, just a small fan with moulded plastic clips on the bottom to attach it directly to the ceramic CPU package. – mnem Aug 17 '17 at 16:02
  • @mnem The DX2-50s didn't need a heatsink. The DX-50s did... I had both DX2-50s and a DX-50 and the DX-50 ran MUCH hotter. – Brian Knoblauch Sep 7 '17 at 11:44
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    Yep. Often confused by people who didn't follow the early-90s PC market: The 486DX-50 is a 50MHz FSB (known nightmare in VLB systems!) and actually more powerful than the 25MHz FSB 486DX2-50. Also, while 3.3V -S versions of both existed, a DX50 build was very likely 5V, while 3.3V builds were not uncommon in the DX2 era. – rackandboneman Sep 7 '17 at 12:50
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Mine did. I recall saving it when I scrapped the PC, and later drilling and tapping holes in the copper base to repurpose it. I recall it was about 2 or three inches square, and had fins about an inch tall. It was a large but conventional looking heat sink, before the fancy stuff started appearing for CPUs.

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Yes you need a heatsink, but no you don't need a dedicated CPU fan.

I remember being flabbergasted at a DX4/100 with what would be called a "northbridge heatsink" with a flat base about 1" square, and fins rising 1" high. It was coloured blue and made of anodised aluminium. And it was absolutely massive for the day.

Related - I once broke an intel DX2/66 overdrive chip into three pieces trying to remove the bonded 8mm heatsink. Sometimes the factory heatsink is epoxy-bonded to the packaging rather than being held on with any clamp.

  • 1
    Would you mind if I asked what gomsagging is? – Dent7777 Aug 17 '17 at 19:09
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    @Dent7777 sorry might have been a bit localised word. "Gazing, open mouthed, silent and gesturing" Have updated answer – Criggie Aug 17 '17 at 20:55
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    No apology needed. That a stylin word right there. Mind if I grab a copy? – Dent7777 Aug 17 '17 at 21:04
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    @Dent7777 go for it. Remember its a New Zealand word is all :) – Criggie Aug 17 '17 at 21:09
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Yes, you need a heatsink. Most 486 heatsinks were so small that they latched directly over the CPU die, so many motherboards had no apparent mounts for a heatsink. Back then, CPUs didn't have the thermal throttling we find so convenient today, so running a cpu without heatsink can end up bad.

486 could be ran without the sink only if airflow was large enough to make up for that. So, without heatsink you need even louder fan.

Note the 4 tabs that are supposed to grip the substrate. You mount the CPU in the sink before putting it into the socket (could be hard if your socket is not ZIF).

http://www.evercoolusa.com/?p=2038

https://www.pimfg.com/product-detail/COOLER-1000

BTW 100MHz DX4 (33x3) was the fastest 486 sold by Intel, but AMD produced 120MHz (40x3). Not that you can't try OCing yours : )

To lower the overall noise, you can (and should) replace the worn-out fan in your PSU or even repurpose early ATX psu.

1

For me it needs a heatsink and also a little fan.

I remember my first PC was a Pentium 90 (I still have the CPU). It has a little heatsink and a little quite noisy fan. Also, why does the MB have the fan controller? Is for connecting the fan, so... And as I remember well the 486DX2 was quite the maximum Intel was able to put out from the 486 so they are running in quite extreme condition, so they became hot very easy. Also remember that was the time when the power consumption was on the low priority for this CPU (notebooks were very rare).

  • Wikipedia links to datasheets.chipdb.org/Intel/x86/486/datashts/27277101.pdf which in table 19 gives required power supply as 1450 mA maximum at 100 MHz, and table 17 specifies an operating voltage of 3.3 V ± 0.3 V. That gives a worst case power dissipation of about 5.2 W. Some variants were 5 V; even assuming same current (not plausible), that still gives <8W dissipated. Your 486 may have been a different variant, but this still gives an idea. Direct Intel thermal design power figures in terms of wattage seems to be a more recent invention. – a CVn Aug 17 '17 at 19:18
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When I built PCs back in the days, the first CPU to require a heatsink was in fact the DX4-100. It would run (without HS) on a normal load and case opened without issues, but closed case and some prolonged gaming or CAD would overheat it. The first heatsink applied had no paste, only a clip-on, no fan, covering the CPU areawise and about 2cm high. After that it worked flawlessly.

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From personal experience:

My first 486 was a 486 SX-20, it did have a heatsink, but with blades only 1 cm high, or so. Later 486s did sport bigger ones, but they did not yet need a fan, really. Typically, the airflow from the PS-fan was enough to cool the CPU. Unless you overclocked the CPU, a practice that began appearing in those days. Fans started appearing in general use, AFAIK, with Pentium processors.

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