The Intel 440BX chipset has been with us ever since it was introduced in May of 1998.  This is quite unusual for a Slot-1 chipset since the first two chipsets for the Pentium II never lasted more than a few months.  The first Pentium II chipset, the 440FX, lasted only a few months, from the introduction of the Pentium II until August of 1997 when the 440LX chipset made its debut.  The latter managed to stay alive for 7 months before being replaced by the 440BX chipset.  So why is it that the BX chipset has been around for an incredible 24 months and is still being used by motherboard manufacturers?

In order to answer that question you have to go back to the theory that necessity is the mother of invention. 

Intel needed a chipset for the Pentium II and they needed it at the release of the CPU in May and not a few months later.  What they ended up doing was taking the 440FX chipset, otherwise known as the Natoma, which was used on entry-level Pentium Pro motherboards and presented it to motherboard manufacturers as a Pentium II solution as well (because of the fact that the Pentium II used the same bus as the Pentium Pro). 

While the Pentium II was gaining momentum, Intel was working on implementing a "new" graphics bus into their next 440 chipset, which ended up being the 440LX, the world's first AGP enabled chipset. 

The upgrade to the BX came about because Intel felt the need to leave the limiting 66MHz FSB of the Pentium II 333/300/266/233 behind and replace it with a faster 100MHz FSB frequency.  This increase in FSB frequency would not only lower the clock multiplier of future Pentium II CPUs but it primarily offered a higher bandwidth data path from the CPU to the chipset and to the memory.  With the AGP bus taking up to 533MB/s of system bus/memory bandwidth, the 533MB/s of available memory bandwidth on the 66MHz 440LX chipset could potentially become a limiting factor; by increasing the system bus and memory bus operating frequency to 100MHz, the amount of available memory bandwidth also increased to 800MB/s. 

The next step in the evolution of Intel chipsets came with what was then known as the Camino chipset, the successor to the popular BX.  It was originally thought that the Camino chipset, now known as the i820, would offer everything the BX chipset had to offer while adding 133MHz FSB support as well as Ultra DMA 66 support.  As more information was released, it quickly became known that the i820 would support a brand new type of memory, RDRAM, but at the same time, the chipset would be able to work alongside SDRAM. 

While all of these rumors ended up coming true in one sense or another – i820 did add 133MHz FSB/Ultra DMA 66 support and it did support SDRAM in addition to RDRAM (however only if a Memory Translator Hub was implemented on the motherboard) – the fact of the matter was that the i820 as a platform was not affordable enough (thanks to the high price associated with RDRAM), didn't offer a large enough performance improvement over the 440BX, and its even poorer performance and possibly instability when used in conjunction with SDRAM and an MTH made this chipset a highly undesirable solution, even by motherboard manufacturers. 

This put motherboard manufacturers in an interesting situation.  Intel was obviously pressuring them to promote and sell as many i820 motherboards as possible yet they couldn't since there wasn't a great enough demand for them.  VIA began offering their Apollo Pro 133A chipset to motherboard manufacturers that needed 133MHz FSB support without having to move to i820.  Unfortunately, in the usual manner of VIA chipsets, the Apollo Pro 133A's overall performance was not the best, and in a head-to-head comparison, at the 100MHz FSB the Intel 440BX chipset would actually pull out ahead.

The only real advantage VIA's 133A offered over the 440BX was that it officially supported the 133MHz FSB frequency, and with the 1/2 AGP multiplier, that would allow the AGP bus to operate within spec when the FSB is set to 133MHz (133/2 = 66MHz = AGP spec clock speed). 

Even the first BX motherboards ever released featured unofficial support for the 133MHz FSB setting, but there was a lack of memory that could run at that frequency (as memory was just starting to ship as PC100 compatible) as well as a lack of AGP video cards that were capable of running at 89MHz, which is what the AGP bus would operate at when the FSB was raised to 133MHz (133 * 2/3 = 89MHz = 35% over 66MHz spec). 

BX at 133MHz
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