Original Link: https://www.anandtech.com/show/250
We all know what it feels like, you're sitting out in your backyard one day, trying to get rid of that annoying neighbor that can't seem to stop bothering you about borrowing your lawnmower and you accidentally let it slip. At the blink of an eye, the bark of a dog, and the quick blow of the wind you immediately realize the mistake you've madeyou've made a promise that you absolutely don't want to keep. Now you're in a lose-lose situation, you can't retract your promise, as that would make you look horrible in the eyes of your elated little neighbor, and at the same time you don't want to part with your cherished lawnmower. You're now stuck between a rock and a hard place, and it's the nature of the human psyche to attempt to rationalize a situation or a particular action in order to make the mind believe that it's doing nothing wrong. So what do you do? You let the friendly old neighbor sit around waiting to cash in on your promise until one day, a few years later, when that old lawnmower has long since been retired, you knock on your neighbor's door with the keys to your shed. Sound familiar?
| Well, if you've never owned a lawnmower and don't happen to have a classic neighbor like the one just described, then maybe you can relate to this story in another manner. Have you ever owned an Intel Pentium Pro? Remember the feeling of joy you got when Intel promised an upgrade path to your expensive investment in the now deserted Socket-8 platform? |  |
| Now, years later, we are finally able to cash in on Intel's promise of an upgrade path for Pentium Pro users. While all your friends were at home speeding along with their Pentium II's you were left with an empty promise that was left as one until just recently. Well folks, it's time to cut the grass, guess who's finally come knocking on your door? | |
A Look Back - The Pentium Pro
| If you take a look at the marketing structure of Intel's processors currently in production, the division among the low-end, midrange, and high-end processor solutions makes sense. Although the structure doesn't always end up being implemented as it should, such as in the case of the Celeron processors which ended up being used as overclocked midrange systems among the tweaker population in our little community, the idea of gearing certain processor lines towards specific types of users makes the efficiency of the processors' usage greater as they are more accurately targeted towards your particular needs. |  |
| The theory first originated, at least in the case of Intel, approximately four years ago, with the announcement of the Pentium Pro processor. Originally appearing in engineering samples rated at 133MHz, the Pentium Pro was designed to be a high-end version of the already successful Pentium line of processors. The full-fledged debut and public implementation of the Pentium Pro actually came around in 1996 at a 150MHz-clock speed, to coincide with the rising clock speeds of the Pentium processor. | |
What separated the Pentium Pro from the Pentium classic (as it has been referred to since the introduction of the Pentium MMX) was the fact that the Pentium Pro had on-chip (albeit not on-die) level 2 cache memory as opposed to the level 2 cache that remained off the chip of the Pentium. As we already know, from the discussions of the Intel Celeron, the Celeron A, and even AMD's K6-3, the speed of the L2 cache is at a direct relationship to the overall performance of a processor, since the L2 cache is used as the high-speed storage area for frequently accessed data. Doesn't it make sense for the most frequently used data to be stored in the fastest memory locations in the system? It should. For a quick description of the primary function of a processor/system's cache, let's take a look at an excerpt from AnandTech's AMD K6-3 Review:
Cache is nothing more than high speed memory that is located closer to your CPU for faster access to frequently used data. The first place your CPU looks for data is in the cache, and more specifically, the cache located on the CPU itself, referred to as Level 1 or L1 cache. If the data the CPU is looking for isnt present in the L1 cache, or it fails to retrieve it in the current clock cycle, it then looks for it in the secondary cache, if present, otherwise it retrieves it from your system memory. Assuming that there is a secondary cache present (L2 cache), the processor can then retrieve it from a source slower than that of the L1 cache, yet still faster than if it had gone all the way to the system memory to retrieve the data. This process continues with however many levels of cache your system has before the processor has no other option than to retrieve the data from system memory, the slowest option out of them all.
By including the L2 cache in the physical package of the Pentium Pro (at the time, integrating L2 cache into the die of the processor itself was not a viable option due to the manufacturing process of Intel's core) Intel managed to outfit the Pentium Pro with an introductory 256KB of L2 cache running at clock speed. Once the Pentium Pro rose in clock speed, so did the amount of cache available for the truly high-end users, Intel began offering 512KB versions of the Pentium Pro at approximately twice the price of a regular Pentium Pro with 256KB of L2 cache, and sometimes in upwards of quadruple the cost of equivalently clocked Pentium processors. It came to the point, that a 200MHz Pentium Pro was made available with a full megabyte of L2 cache, at a price that, even today, still rivals the most expensive Pentium II and Pentium III processors. One could be led to believe that the Pentium Pro would be a complete failure because of its cost, but the Pentium Pro was quite the contrary, it was a highly successful processor among those users it was intended for. The Pentium Pro found its way into servers, high-end workstations, as well as the homes of graphics artists, and those users that happened to have an annoyingly large budget for computer equipment.
Today, Intel has avoided this problem of cost by integrating the L2 cache in the die of the processor, rather than packaging it beside the core of the CPU, however at the time, this seemed to be the best option. You can think of the Pentium Pro, as the Pentium II, with it's cache sitting quietly beside the processor, except instead of the black casing around the Pentium II, you have the ceramic casing around the processor and cache.
As you might be able to guess, the Pentium Pro was considerably larger than its little brother, the classic Pentium (that cache had to go somewhere). In addition to the physically larger size, the Pentium Pro required a new bus architecture, Intel hoped to improve the multiprocessor performance of their Pentium bus architecture as well as CPU to cache data transfers with the new P6 bus and they did so with the Pentium Pro. As a result, the memory and cache performance of the Pentium Pro was dramatically greater than that of the old Pentium, however the cost of the processor kept most desktop users away from the realm of the Pentium Pro. The extremely large and long forgotten interface the Pentium Pro used was dubbed Socket-8.
The Situation at Hand
So Intel had a dilemma on their hands, like the neighbor that promised a lawnmower, Intel promised the Socket-8 users of 1996 and beyond an upgrade path to something better. While the patient investors in the Pentium Pro's now outdated technology waited for that anticipated "knock" on their doors, the rest of the market went crunching away with the migration to the Slot-1 architecture of the Pentium II or the Super7 architecture of the K6. Even at the introduction of the official replacement to the Pentium Pro, the Pentium II Xeon (which used an even larger interface, Slot-2), the users that once invested thousands of dollars into their "bleeding edge" processors were left out in the dust with an empty promise. From time to time, there would be the occasional rumor of the highly anticipated OverDrive processor for Pentium Pro users, however it seemed as if the stories were nothing but what they were classified as, rumors.
Luckily, late in 1998, Intel made the official announcement that the Pentium II OverDrive processor would finally make its debut. Since then, there has been little talk about the processor upgrade, and the release was hardly publicized, possibly because of a powerful "encouragement" to push users towards Slot-1 and away from upgrading the unsupported Socket-8 platform. In fact, if you pay a visit to Intel's Pentium Pro FAQ, you'll notice a large number of broken links, including a now removed General Background Questions section about the processor. It looks like the Pentium Pro has been tossed in Intel's great big retirement home…although not yet forgotten with the introduction of the Pentium II OverDrive.
The OverDrive
The original Pentium Pro processor never made it up above 200MHz, and 98% of all Pentium Pro motherboards never supported Front Side Bus frequency settings (back in the days of the Pentium Pro, it was just referred to as the "Bus" speed) above 66MHz. If you were lucky, your motherboard had support for the 3.5x clock multiplier so you could take your Pentium Pro 200 up to 233MHz if you had proper cooling, but that was pretty much it when it came to upgrading your system. Why not go out and buy a new motherboard and CPU and start all over with a nice Pentium II system? The problem with that solution was that, as many of you will be able to relate to, most users had a tremendous investment in Pentium Pro motherboards, especially those with on-board SCSI/RAID, as well as incredible amounts of EDO DRAM in excess of 512MB at times, so going out and replacing things like that with newer motherboards and half a gigabyte of SDRAM isn't the most economical solution. This is where Intel's idea of the OverDrive processor comes in.
Intel's goal for the OverDrive line of processors has been to provide a processor, with the on-board circuitry to configure itself, requiring only that the FSB frequency be provided by the motherboard. OverDrive processors are basically next generation, or later generation processors, stuck on a circuit board that allows for the processor to adapt to its environment to the extent that the OverDrive processor should be able to work perfectly in any system it is installed in. The goal is obviously extremely idealistic, and likewise, unattainable, however it does provide the basic outline for the functionality of the Pentium II OverDrive processor.
The Pentium II OverDrive
The original Pentium Pro suffered from extremely poor performance under 16-bit applications and even under situations where mixed 16/32-bit application code was present. This kept the Pentium Pro from excelling above the level of the Pentium, clock for clock, under Windows 95 and even under Windows 98. The problem was much less pronounced under Windows NT, which is entirely 32-bit native code, however one thing was for sure, the Pentium II OverDrive for Pentium Pro users had to address this issue.
By using the 0.25 micron Deschutes core of the Pentium II, Intel managed to put a quick end to the 16-bit weakness of the Pentium Pro, and in doing so, they also managed to double the amount of L1 cache on the processor. If you recall, the Pentium Pro, like the original Pentium processors, was only outfitted with 16KB of L1 cache split evenly between Data and Instruction Set caches. The Pentium II OverDrive, like the Pentium MMX, the Pentium II, and the Pentium III, features a full 32KB of L1 cache, once again, split evenly among its Data and Instruction Set caches (16KB + 16KB).
A problem with using the Pentium II core on the OverDrive processor was that there would be no way a Pentium Pro user would agree to making an upgrade to a processor whose cache ran at 1/2 clock speed while their aging Pentium Pro ran its L2 cache at full clock speed. Intel worked around this little problem by making the Pentium II OverDrive nothing more than a Pentium II Xeon on a much smaller scale, using the Pentium II's design to place the L2 cache externally off of the CPU, but on a card that would allow it to operate at the same clock speed as the CPU itself. Owners of the Pentium Pro 200 with 1MB of L2 cache may want to think twice before considering this upgrade, as the Pentium II OverDrive is outfitted with 512KB of L2 cache which should be an improvement for most Pentium Pro users as the 256KB processors were quite popular.
The Pentium II OverDrive, although officially offered in two flavors, a 300MHz and a 333MHz version, is essentially a single 333MHz processor with L2 cache that is intended to run at 333MHz. The chip has a built in clock multiplier of 5.0x, and it derives its clock speed based on your motherboard's set FSB frequency. It is because of this that owners of 150MHz and 180MHz Pentium Pro processors can stick the OverDrive in their systems and have it run at 300MHz, while 166MHz and 200MHz Pentium Pro owners can do the same and have a 333MHz upgrade. Since the 150/180MHz chips use a 60MHz FSB, and 60MHz x 5.0 = 300MHz, and since the 166/200MHz chips use a 66MHz FSB, and 66MHz x 5.0 = 333MHz, the processor works both ways. If you happen to be the owner of a 60MHz FSB Pro and if you happen to have a little knowledge about your motherboard, you're better off jumpering your board as if you had a 66MHz FSB processor (i.e. setting up your 150 as if it were a 166) and then sticking in the OverDrive processor for a small performance improvement.
Meeting the Requirements
The first thing you need to do, before wondering about what to do with your old Pentium Pro processor after you've upgraded it, is to make sure that your system can accept the Pentium II OverDrive. For starters, you must have a Socket-8 motherboard, all previous Pentium Pro motherboards including those without ZIF (Zero Insertion Force) sockets will not accept the Pentium II OverDrive, the easiest way to tell if you have a Socket-8 motherboard is to first consult your manual or look at the socket itself, it should say Socket-8 on it.
The second item to take into consideration is BIOS support for the Pentium II OverDrive, very few mainboard manufacturers that made Pentium Pro motherboards ever followed up with the introduction of the Pentium II OverDrive with a BIOS update. AnandTech's tests used an Octek Rhino P6 Pro Pentium Pro motherboard that did support the Pentium II OverDrive processor, however in the case of many motherboards, the upgrade will either go undetected or improperly detected, often resulting in only 1/2 of the L2 cache being enabled. Your best bet is to take the issue up with your mainboard manufacturer, however you must be sure before slapping down the cash to buy this costly little upgrade as returning an item such as an OverDrive processor isn't always the easiest thing to do, especially when dealing with online vendors.
Owners of multiprocessor Pentium Pro systems will be faced with a bit of a more complex decision to make, the Pentium II OverDrive processor is certified for use in up to dual processor configurations. If you happen to have a dual processor system, you can upgrade it using two Pentium II OverDrive processors, or you can use a single OverDrive without a companion (you cannot pair an OverDrive and a regular Pentium Pro). At the same time, this means that quad processor Pentium II OverDrive setups are not certified for operation and may not work. At the time of publication AnandTech did not have a quad processor Pentium Pro motherboard for verification of any problems with the chip in 4-way multiprocessor configurations.
The Installation
AnandTech's original Pentium Pro system consisted of a Pentium Pro 180, with 256KB of L2 cache running at 180MHz, on an Octek Rhino P6 Pro Socket-8 motherboard based on the Intel 440FX Natoma Chipset, a 4MB PCI Matrox Millennium II, a PCI Ethernet adapter, an ISA Sound Blaster 16, and 2 - 32MB 60ns EDO SIMMs for a total of 64MB of RAM. A few years ago an identically configured system could have been considered top-notch, however in today's market, AnandTech's system was in desperate need of an upgrade.
| The installation of the Pentium II OverDrive consisted of nothing more than removing the Pentium Pro 180, and replacing it with the upgrade. The processor itself came with a quick installation pamphlet that basically diagramed the same simple installation process. The heatsink/fan combo on the Pentium II OverDrive is a very quiet unit and performs an adequate job of cooling the already cool running 0.25-micron processor, the fan is powered by a 5-pin hard drive pass-through power connector. |  |
The Test
The Socket-8 Test System Configuration was as follows:
- Intel Pentium Pro 150, 166, 180, 200 (256KB L2)
- Octek Rhino P6 Pro 440FX Based Socket-8 board
- 64MB EDO DRAM
- Western Digital Caviar AC35100 - UltraATA
- Matrox Millennium II PCI Video Card (4MB)
- Canopus Pure3D-2 Voodoo2 (12MB)
The Socket-7/Super7 Test System Configuration was as follows:
- AMD K6 233, AMD K6-2 350, AMD K6-3 450 (engineering sample)
- FIC PA-2013 w/ 2MB L2 Cache
- 64MB PC100 SDRAM
- Western Digital Caviar AC35100 - UltraATA
- Matrox Millennium G200 AGP Video Card (8MB)
- Canopus Pure3D-2 Voodoo2 (12MB)
The Pentium II comparison system differed only in terms of the processor and motherboard in which case the following components were used:
- Intel Celeron 300, Intel Celeron 300A, Intel Pentium II 400, Intel Pentium II 450
- ABIT BH6 Pentium II BX Motherboard
The following drivers were common to both test systems:
- MGA G200 Drivers v1677_426
- DirectX 6
The benchmark suite consisted of the following applications:
- Ziff Davis Winstone 99 under Windows 98 & Windows NT4 SP4
- Quake 2 v3.19 using demo1.dm2 and Brett "3 Fingers" Jacobs Crusher.dm2 demo
All Winstone tests were run at 1024 x 768 x 16 bit color, all gaming performance tests were run at 800 x 600 x 16 bit color. 3DNow! support was enabled when applicable.
Windows 98 Performance
As you can tell, the Pentium II OverDrive's performance under Windows 98 is a welcome improvement from the speeds of the original Pentium Pro processors. Comparatively speaking, due to the faster L2 cache, the Pentium II OverDrive is slightly faster than the Pentium II at equivalent clock speeds under Windows 98.
Gaming Performance
The FPU performance of the Pentium II OverDrive is an improvement over that of the Pentium Pro, however there have not been any major tweaks in the FPU of Intel processors since the introduction of the Pentium Pro, meaning that the only real gaming benefit the Pentium II OverDrive offers is a higher clock speed (provided that we dismiss MMX as a beneficial feature).
Windows NT Performance
A similar picture can be found under Windows NT, where the Pentium II OverDrive extended the life of AnandTech's Pentium Pro system by raising the bar of competition the system had to offer. However, as mentioned before, the limited improvements in the FPU of the Pentium II OverDrive over the original Pentium Pro keep the High End Winstone 99 improvements to a minimum.
The high-end multiprocessor ready applications test flew on the OverDrive processors, often scoring in excess of 35% faster than the previous Pentium Pro system without the upgrade. As long as you're not expecting a huge 100% increase in performance, the Pentium II OverDrive should be able to give you your money's worth provided that you are of the select few users that could actually benefit from the Pentium II OverDrive…
Conclusion
Who should buy the Pentium II OverDrive? At a price tag of over $500, the Pentium II OverDrive does not come cheap. If you happen to be a fairly normal user that spent a few thousand dollars on a Pentium Pro system that is now grossly out of "style" and happen to have a few hundred dollars for an upgrade, you'd probably be better off getting a new Pentium II, motherboard, and SDRAM and re-using all of your old components (i.e. video/sound cards, etc…). If you happen to have a workstation with a minimum investment placed in it, as in you don't have 512MB of RAM to worry about going to waste, then pursuing a new Pentium II system would be the ideal choice. The only time you would want to consider the Pentium II OverDrive is if you happen to have a large sum of money invested in your single/dual processor Pentium Pro system or happen to require the faster cache of a Pentium Pro (i.e. a server), in which case, the Pentium II OverDrive, albeit a highly expensive solution, would come in quite handy. Keep in mind that the Pentium II OverDrive is nothing more than a Pentium II Xeon that fits into a Socket-8 running at 333MHz. Who would have thought that Intel would come knocking at the doors of all of the old Pentium Pro users with the Xeon they never imagined they would be able to upgrade to.
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