20MHz; one of the slowest 486 chips available (there are 16MHz parts as well). Thankfully it didn't sell well because it is quite a lot slower than the SX25. It's only a difference of 5MHz but remember that the front-side-bus (FSB) is also 5MHz slower. This will cause the impact to be bigger. > Read more

A 25MHz 80486 SX processor. Not very fast but it's not the slowest 486 ever made. This one runs 5MHz faster which is noticeably in applications. The SX25 could be overclocked to 33MHz quite often without any hassle. 8MHz may not sound much but will greatly improve the speed of the system. Especially as the front-side-bus (FSB) goes up to 33MHz as well. In case the system is equipped with a Vesa Local Bus (VLB) graphics card the VLB bus goes up to 33MHz as well. In my opinion this is quite an ideal situation for a PC as the processor can ship it's data to the rest of the system as fast as possible because everything runs at the same speed.

The 486 had several improvements over the 386DX. Except for the SX versions it featured an internal co-processor. Both the SX and DX versions had internal cache, branch prediction and a five-stage pipeline. The internal cache (8KB) functions as a buffer for small data. Because the cache is inside the processor it can be accessed with higher speeds compared to the normal RAM. With branch prediction the processor will think in advance and get everything ready for the coming instructions. Pipelining is something that every modern CPU uses. See it as extinguishing a fire: without pipelining you have to fill a bucket of water, walk to the fire and dispose the water. With pipelining one fill the bucket, gives the bucket to the person standing next to him, he gives it to the person next to him and he gives it to the one that throws the water on the fire. This method of working will speed up the processor. > Read more

Same as this SX 25 but with a different sSpec number and that it's more than two years older. > Read more

The SX33 was quite a good processor for a while. Both AMD and Cyrix made 33MHz parts as well but DX/2, DX/4 and even DX/5 parts from these companies can be found more easily. This is because AMD and Cyrix had to make their own 486 because Intel didn't gave the 'howto make a 486-manual' to AMD and Cyrix anymore. Both companies used the 386 as a foundation for their 486 processors and thus shipped their 486 on the market two years later. At that time the DX and DX/2 processors were becoming more popular.

Intel's SX33 processor was quite popular at the time. It is noticeably faster than the SX 25MHz. > Read more

Exactly the same as the SX33 execpt for the integrated co-processor. This co-processor is used for floating point calculations. At the time normal applications didn't use the FPU (floating point unit) so people had enough power with only the, much cheaper, SX 33MHz processor. After all Doom ran just as good on a SX as on a DX; Doom didn't use the FPU. > Read more

Both the Am486DX40 and Cx486DX40 were tricky on early motherboards because of their high bus speed. Think again and look at this 50MHz part that requires a 50MHz front side bus. 50MHz sounds like it will fly but unfortunatly it doesn't.

My UMC PCI motherboard automatically sets the PCI bus on 25MHz (1/2 of the FSB) when running a 50MHz FSB. This is because the PCI slots are rated to run at 33MHz and the next step would be 37,5MHz (1/3 of the FSB). This affects performance of the cards that are installed, especially the graphics card. With a 25MHz PCI bus Doom 1.9S will score 24.91 FPS. The same benchmark with 37,5MHz PCI bus gets 26.17 FPS. All the benchmarks run by this CPU shown below are done with a 37,5MHz PCI bus.

Notice that the DX50 isn't much faster than the DX2/50, even though it runs at twice the bus speed (50MHz over 25MHz)! Only Doom seems to run a bit better but that's because the graphics card can be accessed faster over the 37,5MHz PCI bus. > Read more

This CPU won't be seen very often. Most people either bought the SX/DX33 or went for the DX2/66MHz. The DX2/66MHz was quite powerful and noticeably faster than the DX2/50MHz and thus worth the extra cash.

The SX2 doesn't have an integrated floating point unit (FPU) like any other 486SX CPU. Besides that it is exactly the same as the DX2.

To get a higher clock frequency the SX2 and DX2 use a technique called 'clock doubling'. This involves a multiplier that sets the clock frequency at twice the frequency of the front side bus (FSB). In this case a SX2/50 uses a 25MHz FSB and the CPU itself runs at twice the speed. The DX2/66 uses a 33MHz bus and weirdly enough the DX4/100 uses a 33MHz bus as well. Marketing-wise the name DX4 sounded better than DX3 but technically the DX4 is actually clock tripled like the non-existing DX3 would be.

> Read more

The same as the 80486SX2/50 but with floating point unit (FPU) on-board. The FPU is used for floating point calculations and comes in to play with CAD and Excel. Back then games didn't really use it yet so Doom will run pretty much the same on a SX2. Quake does require a FPU but 486's are practically too slow to run Quake at a decent frame rate. > Read more

A popular processor in the 486 era. The DX2/66 was able to run lot's of games and applications quite well. Doom runs a lot smoother on a system with a DX2/66 fitted instead of a DX33.

This 486DX2/66 is less common because it has a nice blue heatsink attached. Most DX2/66 CPU's didn't had a heatsink mounted by Intel but a 3rd party heatsink or heatsink/fan solution.

There are two major versions of the DX2. The P24 and P24D of which the latter has a faster L1 cache mode called write-back that improves performance. The P24 version only offers write-through cache which is slower. The 'SX731' (this model) is the P24. See this 486DX2/66 which is a P24D. > Read more

Unlike this 486DX2/66 it has no build on heatsink. This allowed people to stick their own heatsink/fan solution onto it as the 486DX2/66 didn't run happy without heatsink.

This version of the DX2/66 is the fastest Intel ever made. See the benchmarks where it is ahead on the other DX2/66. The performance difference can be declared because the DX2/66 came in two version. A P24 and P24D. Difference is that the P24 only has write-through L1 cache and the P24D has write-back L1 cache, which is faster. > Read more

This is not the first 66MHz CPU in my database. In fact it's the third Intel 486DX2/66. The other two have a different sSpec number and one of them is faster than usual because it has write-back cache. > Read more

The first 100MHz ticking part Intel brought onto the x86 market. The DX4/100 was actually a DX3/100 as it didn't clock quadruple but clock triple the front side bus frequency.

In many cases an old 486 couldn't be upgraded to the DX4/100. Not only because some motherboards didn't understand the clock doubling or tripling technique, also because the voltage requirements changed. Older 486 processors use 5V on the core instead of 3V for this DX4/100. Of course it did boot up at 5V but it can damage the chip. Not to mention the excessive heat output it generates at 5V! > Read more