On April 15, Intel released their Pentium-II 350- and 400-mhz chips and their new BX chipset (required to run the new Pentium-II 350 and 400). One important feature in the BX chipset and the new Pentium-II processors is the addition of a 100-mhz bus speed. For a long time the bus speed has been stuck at 66 mhz and the release of the BX chipset is the first official 100-mhz release. Both Intel and AMD promised 100-mhz bus speed CPUs by the end of 1997, but they are only emerging onto the market now. The upcoming K6-2 from AMD is planned to run on a 100-mhz bus speed. The 100-mhz bus-speed release has been long awaited by many hard-core computer users, but is the increase worth an upgrade? What's so great about the jump to a 100mhz bus-speed?

First, I'll explain what the bus speed actually is. The bus speed is the speed at which the CPU is communicates with other motherboard components (chipset, RAM, etc.). Since it affects more than just the processor itself, a faster bus speed affects overall system performance. Because of this, many overclockers use bus speeds of 75 or 83 mhz to increase performance. There are two main reasons why performance is increased. One is because the L2 cache speed is directly effected by the bus-speed. However, this only occurs on Socket 7 systems where the L2 cache is off the CPU, on the motherboard itself. In Pentium-II and Pentium Pro systems, the L2 cache is on-chip and set at half the processor speed. Secondly, the PCI bus runs at 33 mhz, or half the bus speed. When the bus speed is bumped up to 75 mhz or 83 mhz, the PCI bus runs at 37.5 mhz and 41.5 mhz respectively. Some PCI cards don't run stably at the higher speeds, but the ones that do (many do), benefit from the faster speed.

So, with the new Intel Pentium-II processors running at a 100 mhz bus speed, they should go faster right? Well yes, but not by as much as you would expect. In fact, the main performance increase is gained from higher overall clock speeds. Since the L2 cache is built onto the Pentium-II chip and its speed is set to half the processor speed and not affected by the bus speed, the faster bus speed doesn't help to speed up the L2 cache. Additionally, for stability of the PCI bus, the PCI bus runs at one-third of the bus speed or at good old 33 mhz. Where the bus speed really helps in Pentium-II systems is with AGP. At a 66-mhz bus speed, the maximum data transfer rate of AGP would be 8x66 mhz or 528 megabytes per second (8x mode, not available yet, but coming in the future). With a 100-mhz bus speed the maximum data transfer is increased to 800 mb/s. The performance increase also helps at the current AGP 1x or 2x modes, where the speed increases from 66 mhz to 100 mhz or 133 mhz to 200 mhz, respectively. On Socket 7 systems (K6, Pentium MMX, and Cyrix's chips), the increase in performance will be much more than in Pentium-II systems. As said before, the L2 cache speed on Socket 7 systems is effected by the bus speed, so the L2 cache speed will increase by 50 percent.