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Should the Pentium II have been socketed?

March 28, 2023 at 6:10 PM
Category: Hardware

Those familiar with processors should know that they generally come in the form of small chips with many pins sticking out (or just gold contacts these days), and such things just drop in to a socket easily. Given this, the form factor of a few lineups of CPUs available from 1997 to 2000 might shock some people, at least those who haven't already seen one hundreds of times.

Intel Pentium II processor

When the first Pentium II CPUs were released, they demanded a ton of space on motherboards, not just for the long slot connector, but also enough for a heatsink to hang over the board. This had to be a controversial design; I talked with someone at a store about these CPUs years ago, and he hated that form. Don't forget too, this was released in a time when the majority of household computers were using the AT form factor. Fitting a Pentium II onto a board like that often required serious compromises, like having less expansion slots. It was clearly made with the newer ATX standard in mind.

Intel Pentium Pro processor

Intel could have ran with their earlier Pentium Pro CPU, as it already supported a wide range of next-generation hardware features like much faster L2 cache, USWC for faster video performance, and the ability to address 1GB of RAM or possibly more without any performance penalties imposed like there would be with external cache on earlier motherboards.

Even so, the Pentium Pro was continuously expensive, so it had trouble breaking into the consumer market. It seems full speed L2 cache was simply too difficult to manufacture at an affordable price for a time, so Intel had to devise a different strategy.

The Cheap Cache Trick

When the Pentium II did make its debut, it immediately showed some clear advantages over the Pentium Pro, including a reduced cost at launch, support for the MMX instruction set, and not being crippled, supposedly, in the execution of 16-bit code.

Although the Pentium II is very much capable of running faster than a Pentium Pro depending on the software being used, the cache memory only runs at half the speed of the CPU clock. To reduce the cost of the processor and improve production yields, the Pentium II relies on external cache memory modules residing on a PCB next to the CPU itself. It's just enough to push the CPU a lot further compared to having cache memory always stuck at 66MHz without jumping too far to the extreme end.

Initially, the only real improvements seen in the Pentium II came from within itself, as it could only be used with motherboards using the 440FX chipset, a carryover from the Pentium Pro era. It wasn't until later in 1997 that the 440LX chipset would debut, allowing this CPU to truly realize its potential.

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The new chipset supported the much faster SDRAM standard for memory, previously only found in some Socket 7boards, and it introduced support for AGP video cards. Additionally, it had a faster internal IDE controller like the 430TX did, and it appears it was the first one where motherboards started adding proper implementations of ACPI. The 440LX chipset is what would really give the Pentium II its identity as the leader in fast personal computers - at least until 440BX came out soon after, bumping up the front side bus speed to 100MHz to narrow some performance gaps between the CPU and other components.

Was it something that truly needed such a large package, though? Possibly, considering the first generation Pentium II lineup, Klamath, used four separate cache modules at once. By 1998, however, a certain product appeared which could possibly suggest that Intel may have had the option to go a different route.

An Actual Socket Form

Pentium II Overdrive Processor box

Enter the Pentium II Overdrive, a CPU designed as a drop-in upgrade for most Socket 8 motherboards. At this point, the idea of late drop-in replacement CPUs seemed to be a fading concept for most consumers, as the push for them to buy new computers was growing stronger. I've seen a surprising number of these things still new in the box; I guess a lot of people ended up not needing such a thing. It was at this point that Intel terminated their Overdrive lineup entirely.

Pentium II Overdrive installed in CPU socket

The Pentium II Overdrive employed some of its own trickery to make itself fit easily into older Pentium Pro motherboards, many which would have been manufactured in 1996 and possibly even some of the earliest ones from 1995 (I'm not sure if it works on 450KX motherboards). The CPU itself is a bit smaller than it looks on the outside, as it's attached to a PCB - very similarly to how an actual Pentium II would be designed. The PCB hangs right over the socket's label, enough to throw more components on there while still guaranteeing a fit in just about any system.

Running at 333MHz, the Pentium II Overdrive is a shocking boost from the fastest 200MHz Pentium Pro CPUs, but that's what happens when one finally addresses two years of stagnation and brings all the new developments over there. Combine this with MMX technology and 512KB of L2 cache running at full speed, and this thing finally stopped the 440FX chipset from being too much of a dead end. (Why could they get full speed cache here, but not with their normal Pentium II CPUs?)

27 FPS in Unreal on Pentium II Overdrive at 320x240

The fact that it's able to competently handle a game like Unreal in software rendering should show how huge of a jump it is over most any Pentium Pro. It's able to achieve 27 frames per second at 320x240 in software rendering, as much as a 200MHz Pentium Pro with 1MB of cache using a Voodoo2 at 640x480 with Glide!

Part of the PCB is designated to the Overdrive's own voltage regulation, but if you were to take that out, that would leave more room for other things. It begs the question: would Intel have been better off designing the Pentium II like the Overdrive CPU depicted here? For one, reusing an existing socket would mean motherboard manufacturers wouldn't be faced with the cost of a new connector, and the need to create entirely new motherboard designs to account for it. At most, they'd just have to implement a better voltage regulation system, possibly.

For Intel, creating the Pentium II on a socket would also have resulted in a much smaller package, allowing them to ship far more units at once. This smaller package would have also made it easier to design low profile computers, especially those using the NLX form factor for a time. I'm sure there would've been a way to pull it off. Having a CPU and external cache on a board plugging into a socket was the route Apple and IBM chose for most of their PowerPC G3 processors; they were a lot more forward-thinking on that front, that much can be said.

Abit BP6 computer with two Celeron CPUs installed

Eventually, having extra CPU cache set up like that had to have grown increasingly unsustainable. After Intel introducted the Celeron CPU lineup, a lot more systems returned to using purely socketed CPUs in 1999. Before then, AMD and several chipset manufacturers had been filling in part of that socket void beforehand, taking the approach of greatly enhancing the existing Socket 7 platform.

Starting with the Mendocino core, L2 cache was integrated into the CPU die itself. It had far less cache compared to a Pentium II, but this was evened out by the cache operating at full speed. It's surprisingly great for a budget CPU; although it was usually implanted in trashy budget OEM systems, it could be installed in a 440LX motherboard with an adapter. Getting one running at 533MHz could sort of qualify it as an Overdrive CPU for such a platform.

By the time the first Coppermine-based Pentium III CPUs were released, they did still come in slotted packages, but were very much designed with Socket 370 in mind, so as to move past slotted CPU connectors. Eventually, the industry moved past them entirely, and what we're left with is a very bizarre, yet fascinating series of products from a transitional period rooted in trying to get the most out of a powerful CPU through any means possible.

In the long run, Slot 1 CPUs have become a favored entry point for vintage computing because of the design allowing for easy swapping of CPUs that can now be picked up for a reasonable range of $10-$30. If you want to use a different CPU at any point, you just unlock the retention clips and pull the old one out. No need to be mindful of the heatsink, possibly having to replace thermal compound, as the cooler's already attached to the CPU. (Some Socket 7 CPUs had coolers glued to them as well, but they're not as common)

I'm sure that back then, though, consumers maintaining their own computers would not have appreciated the large form factor of the Pentium II, especially if they were to cram a new motherboard into their AT case. If you hate it, you're going to absolutely despise the sheer size of the Pentium II Xeon...

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Bird - April 01, 2023 at 04:19 AM

The Slot 1 is destiny for me. My first computer, a P2 machine from 1999 had it, and a scrap find P3 has it too. Both running perfectly to this day. What are your experiences with the heatsink / thermal paste on those CPUs? To be honest, I never touched them except for blowing the dust out and they have no problems since... 23-24 odd years?

However I don't think that upgrading a Slot 1 CPU was that straight forward. You had to look for the specific retention clips, as they weren't interchangeable between various CPU models.

Also, the P2 specifically is a holy grail, because with the P3, Intel showed an evil face with that Processor Number feature to spy on the users...

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