Pentium II Overdrive: A Home Made Xeonby Anand Lal Shimpi on August 14, 1998 3:14 PM EST
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The Pentium Pro
The Pentium Pro was a highly successful processor during its time, especially for the high end market. It featured a 256KB or 512KB (and later on even a 1MB) L2 cache that operated at the clock speed of the processor. This made the Pentium Pro ideal for server solutions or high end workstations, unfortunately Intel's pricing scheme left the 512KB chips out of the reach of many. Regardless, quite a few hardware addicts put together systems based on the cheaper 256KB versions usually taking advantage of the low cost of the 150 and 166MHz parts. With the relatively low cost of Pentium Pro motherboards, many have taken advantage of the dying Socket-8 standard and managed to get a fairly decent system for the money. An average Pentium Pro motherboard, based on the old Intel 440FX Chipset will set you back around $100, but why would you care now...?
The Pentium II
The Pentium II, contrary to popular belief, was never intended to replace the Pentium Pro. The Pentium II was more of a replacement for the Pentium MMX, the reason behind this being that the Pentium II's L2 cache did not operate at its clock speed, rather 1/2 of the clock speed, making it a weaker performer under server or high end workstation situations. In order to balance the strengths and weaknesses, Intel stopped manufacturing the Pentium Pro at 200MHz and allowed the Pentium II to extend to clock speeds of 450MHz. But if the Pentium II isn't the successor to the Pentium Pro, then what is?
The Pentium II Xeon
Here's the real successor to the Pentium Pro, using a Slot-2 Single Edge Connector (SEC) interface, the Pentium II Xeon is essentially a Pentium II with 512KB, 1MB or even 2MB of L2 cache running at its clock speed, which currently resides in the 400 - 450MHz range. The true definition of a server processor from Intel fits the description of the Pentium II Xeon down to the last dot, but the incredible price of the Xeon ($1300+ for a 512KB 400MHz part) will keep it out of the range of many power users...is there another option?
The Pentium II OverDrive
The newly released Pentium II OverDrive has the potential to become the poor man's Xeon. Just about a year ago, Dan Chadwick over at Tweakit (www.tweakit.com) conducted a test on a Pentium Pro on a Pentium II motherboard based on the Intel 440LX Chipset. This test was made possible by using the ABIT KP6 Pentium Pro - Slot-1 Riser Card, which is essentially a Socket-8 on a processor card with a Slot-1 cartridge pin-out. Tweakit's tests confirmed that the card worked on 440FX motherboards, and it did manage to work on two out of the five LX based motherboards he used meaning that there was a great potential for the Pentium Pro processor, only if the clock speed could be increased. Intel managed to make users want to go for the Pentium II over the Pentium Pro simply by using a clock speed high enough to provide faster overall performance than a Pentium Pro under most situations, however Intel did manage to slip up in their attempts very recently.
The Pentium II OverDrive is nothing more than a 333MHz Pentium II Xeon processor that will fit into a Socket-8 motherboard, the comparison to a Xeon is made due to the fact that the OverDrive runs its 512KB of L2 cache at its clock speed. If you have a 150 or 180MHz Pentium Pro processor, the Pentium II OverDrive will take you up to 300MHz, and if you have a 166 or 200MHz Pentium Pro processor the OverDrive will take you up to 333MHz. Considering that the OverDrive will retail for around $600, there is a definite potential for a poor man's Xeon with this chip...why?
A Home Made Xeon
First of all, you must understand how Intel's OverDrive chips work. You don't need to have an existing processor installed to use an OverDrive processor, the OverDrive is a processor itself which simply contains extra voltage regulators and pre-configured clock multipliers to make sure that the upgrade process is made as easy as possible. How does the Pentium II OverDrive detect whether you had a 150/180MHz chip or a 166/200MHz chip installed prior to purchasing the OverDrive? It uses the Front Side Bus (FSB) speed your system is set to, which will be 60MHz for 150/180MHz processors or 66MHz for 166/200MHz processor, and multiplies it by the 5.0x clock multiplier the chip is locked at. So by setting the jumpers on your motherboard to reflect a 166MHz or 200MHz Pentium Pro before installing the OverDrive you will get the benefit of a 333MHz upgrade.
The Pentium II OverDrive is a 0.25 micron processor, based on the Pentium II Deschutes core which is used in all Pentium II's at 333MHz or higher as well as Celeron and Xeon chips, this manufacturing process has already been proved to have incredible overclocking potential based on previous chips. The Pentium II OverDrive is clock locked at a 5.0x clock multiplier, virtually eliminating the possibility of running it at the 100MHz FSB on a BX motherboard since a 333MHz to 500MHz overclock is highly unlikely. This leaves you with 2 other options, clocking the chip at 75MHz x 5.0 or 83MHz x 5.0 for 375MHz or 416MHz to get the most performance out of it, unfortunately no Pentium Pro board on the market allows for an 83MHz FSB setting...the solution? Get a Pentium II board.
Merc, aka John Morris, made a post to the Intel OverDrive Processor Newsgroup about the possibility of running a Pentium II OverDrive on a Riser Card on a Pentium II motherboard. While he mentioned running it at 100MHz x 5.0 on a BX motherboard, this sparked an idea which could possibly get rid of any possible compatibility problems. The VIA Apollo Pro Chipset, originally designed for use with the Pentium Pro processor and now adapted for use with the Pentium II, would make the perfect companion to this OverDrive processor. The reason being that it fully supports both the Pentium Pro and Pentium II processors according to VIA's documentation on the chipset. While no testing has been conducted by AnandTech on the newly released OverDrive processor, the possibility of running the processor at 375MHz or 416MHz on an Apollo Pro based motherboard makes the OverDrive a definite candidate for a Home Made Xeon.
As soon as a part can be obtained for testing, an update to this article will follow...until then, have a good time hunting for a Pentium II OverDrive processor as it isn't often that a company makes this big of an oversight.