Intel Pentium II 233 – 300 CPUs, Core Codename Klamath
Intel’s first Pentium II CPU with the internal product specification number ‘80522‘ had the codename ‘Klamath’ and is still sold as the Pentium II versions 233 up to 300 Mhz. It has got four second level cache modules with the speed marking of 7 ns and the tag RAM chip 82459AB. Due to the fact that it’s only rated for speeds up to 150 MHz (300 MHz/2), the Klamath’s second level cache timing is the fastest of all Pentium II CPUs, giving it a performance edge compared to Deschutes CPUs at the same clock speed, which of course is academical, since Deschutes starts at 333 Mhz in a Pentium II. The Klamath core is larger than the core of the Deschutes, because it’s still manufactured in .35 micron technology. This is also responsible for the larger heat production of the Klamath, compared to the Deschutes core. The common core voltage requirement of the Klamath is 2.8 V.
Many or most of the Klamath CPU’s have the multiplier restricted, so that you cannot exceed the allowed core frequency as long as the front side bus frequency stays unchanged. Some 266 MHz CPUs can run at 300/66 however, so that some people specialized in counterfeiting the plastic package of a Pentium II 266, selling them as Pentium II 300 CPUs. Usually Pentium II 233 and 266 CPUs come without second level cache ECC and Pentium II 300 are pretty much all sold as second level cache ECC version. Thus c’t-Magazine is asking every owner of a Pentium II 300 to check if their CPU is supplied with ECC level 2 cache, using a little program you can download from their website. If you have got a Pentium II 300 without ECC L2 cache you have most likely got a counterfeit Pentium II 266. This story is pretty valid, although I’ve once bought a Pentium II 266 in San Jose, that is not overclockable, but it has ECC L2 cache although it is only a 266 MHz version.
The Klamath is certainly overclockable, but in most cases it requires the increase of the front side bus frequency, which is dangerous for your PCI and AGP devices, because they run at PCI/AGP clocks above spec. Some crazy people overclock Pentium II 300 CPUs up to 375 MHz and even more. This is certainly an interesting thing to do, alas it is pretty useless for anyone who needs a reliable system. As a crazy overclocker you’ve got to live with the fact that your system can crash any time, if it’s screwing up your presentation for the next morning or ‘only’ a Quake 2 rocket arena deathmatch. The L2 cache, in a Pentium II running at half of the core clock frequency and rated at 7 ns is absolutely not designed for clock speeds exceeding 150 MHz, maybe it will do 166 Mhz in some cases, but don’t expect any reliability of a 7 ns L2 cache running at 175 MHz or even more.
The package of the Klamath core itself shows that the chip hidden under the octagonal metal cover is larger than a Deschutes.
Please note the four second level cache modules, rated 7 ns and the tag RAM chip on the opposite side of the CPU, saying ‘82459AB’. You will not find the resistors that differentiate a 66 from a 100 MHZ front side bus CPU. The Klamath is only rated for 66 MHz FSB and thus the PCB has the FSB detect Pin ‘B21’ hardwired to 0 V. Intel Pentium II 333 – 400, Core Codename Deschutes.
Intel managed shrinking the core of their 6th generation MMX CPU to 0.25 after the Klamath was on the market for roughly 8 months. This resulted in higher core frequencies, lower voltage requirements and less heat production. However, higher core speeds mean higher second level speeds as well, so that Intel needed to change the modules for the second level cache as well as its timing. The new L2 cache modules are packed at a higher density, so that only two modules are required. These new modules are rated 5.5 ns for 333 and 350 MHz Pentium II CPUs and 5 ns for 400 MHz Pentium II CPUs. The tag RAM chip has changed as well, the 333 and 350 MHz Pentium II is using the newer 82459AC tag RAM, the 400 MHz version comes with the latest and fastest 82459AD chip.
The new generation of Pentium II CPUs is now running at 100 MHz front side bus, whilst the Klamath as well as the Deschutes at 333 MHz are only supposed to run at 66 MHz FSB. Intel’s BX chipset is able to recognize which kind of CPU is plugged into the motherboard, so that most BX motherboards are following the Intel spec and supply the correct front side bus frequency automatically. The detection of the correct FSB clock is done via CPU pin B21, which is on low in case of a 66 MHz FSB CPU and high in case of 100 MHz FSB. In a Deschutes CPU the logical state of pin B21 is determined by two SMD resistors on the CPU PCB, R5 and R6. In case of a Pentium II 333 these two resistors are 0 Ohm, in case of a Pentium II 350 or 400 R5 is 1000 Ohm, R6 is 3,300 Ohm. (Literature: c’t-Magazine, issue 8, page 177) This may be interesting for some very courageous people who want to solder the 1 kOhm and 3.3 kOhm resistors instead of the 0 Ohm ones onto the PCB.
From the Intel Pentium II 350/400 data sheet
As you can see there’s a serious difference between 333 and 350 MHz Pentium II CPUs and its brothers at 400 MHz. The 400 MHz version has got a different tag RAM chip as well as faster L2 cache modules. 5 ns instead of 5.5 ns seems to sound almost the same, but we shouldn’t forget that 5 ns is about 10% faster than 5.5 ns, which comes close to the increase in core clock or L2 cache frequency respectively of 14% from 350 to 400 MHz. This is not the only difference, the 5 ns L2 cache modules are cooled whilst the 5.5 ns modules in the Pentium 333 and 350 aren’t. This is done via a different back plate of the Pentium II 400 single edge cartridge (SEC), which has two special notches that fit directly on the two modules, as you can see below. The third difference is the timing of the L2 cache. As already said above, the L2 cache timing of the Pentium II 233-300 MHz CPUs is faster than the L2 cache timing of the Pentium II 333. Now the timing of the 5 ns L2 cache in the Pentium II 400 is even slower than in the 333 and 350 models. This is something that should be considered by hardware testers that want to use the easily overclockable Pentium II 333 as test CPU for 400 MHz testing, because the benchmark results scored by this overclocked CPU are higher than what you would get with a real 400 MHz Pentium II.
The latest version of Andreas Stiller’s good old low level benchmark program ‘ctcm.exe’ (published by c’t-Magazine) shows nicely the difference in L2 cache speed. Here are the results of the L2 cache speed at 300 MHz core clock, ran on a Pentium II 300, a Pentium II 333 and a Pentium II 400:
Running each of these CPUs in an application type benchmark like e.g. Winstone shows that at 300 MHz, the Pentium II 400 is scoring considerably less than a Pentium II 300 or 333.
This will also be a pretty nice way of finding out if a 333 or 350 MHz CPU was counterfeit to a 400 MHz model. If ctcm shows 280 MB/s for the L2 cache speed, you can be 100% sure that you’ve bought a counterfeit CPU, opening the CPU and finding 5.5 ns cache will finally prove it.
Overclocking of Pentium II with Deschutes CPUs will in most cases also require the increase of the front side bus, since the higher multipliers will most likely be disabled by Intel. The Pentium II 333 has a multiplier up to 5x built in, so that you can theoretically reach pretty high clock rates, as long as a BX motherboard will let you run this CPU at 100 MHz FSB or even more. Motherboards that detect the FSB clock automatically can only be fooled if you should be courageous enough and change the above mentioned resistors on your CPU PCB. I recommend you rather go for a motherboard that let’s you choose 100 MHz FSB or more regardless what CPU is in there. Overclocking is pretty dangerous when you look at the system stability point of view. Intel has got a good reason for using cooled 5 ns L2 cache modules on their 400 MHz part. The CPU core will in most cases do the higher clock rate just fine, however the L2 cache running at half of this higher clock speed will most likely cause erratic behaviour and can easily be the reason for system crashes. I consider everyone as really crazy, who runs his business software on a system with a highly overclocked Deschutes CPU. Nevertheless, keeping in mind that you can run into system crashes at any time, overclocking works pretty well in the following cases:
- Pentium II 333 to 350/100, careful at 400/100 (requires motherboard that let’s you choose 100 MHz FSB)
- Pentium II 350 to 392/112, possible L2 cache issue, possible PC100 SDRAM issue at 112 Mhz
- Pentium II 400 to 448/112, possible L2 cache issue, possible PC100 SDRAM issue at 112 Mhz
People that overclock to more than that either post this to make themselves look important without using the system at this speed or they must be considered as a bit crazy. Reaching higher speeds safely only works with special 7 ns SDRAM modules and a Kryotech cooling system as shown by Intel at CeBIT 98, when they presented the 700 MHz Pentium II system.
The common core voltage of the Deschutes core is 2 V.
This is a Pentium II 333. The green resistors for R5 and R6 are 0 Ohm. You can also see the 5.5 ns L2 cache modules from Samsung.
The Pentium II 400 has the 1 kOhm and 3.3 kOhm R5 and R6 and is sing 5 ns L2 cache modules, also from Samsung.
The back side of this Pentium II 333 PCB shows the 82459AC tag RAM module.
The Pentium II 400 is using the 82459AD tag RAM module.
This is the back plate of a Pentium II 333 to which you mount the heat sink on the other side. You can see the thermal grease where it fits onto the Deschutes core. There are no special notches left and right of it.
The back plate of a Pentium II 400 looks quite a bit different. The bottom part is also aluminium, not an extra plastic part as removed in the picture of the Pentium II 333 back plate. You can easily spot the two notches for the L2 cache modules, both covered with thermal grease. Intel Celeron, Core Codename Deschutes
The Celeron, Intel’s attack on the CPU suppliers of the low end market, comes with the same 0.25 micron core as the Deschutes and is therefore ‘more modern’ than the Pentium II 233-300 CPUs with their 0.35 micron Klamath core. Celeron has not got any L2 cache and is otherwise identical to the other Pentium II CPUs. Thus is can show its strengths when running floating point calculation intensive applications like 3D games in the first instance, a field where it is faster than any currently available socket 7 CPU. The lack of L2 cache results in a decent but not amazing office application performance, but it has got it’s advantages as well. As you learned from the stuff above, the L2 cache is making the most trouble when clocking the Slot 1 CPUs higher. The Celeron doesn’t have to worry about that. Only it’s successor with the codename ‘Mendocino’ will have an internal L2 cache and will hence be more sensitive to higher clock speeds as well. The just said leads to the simple conclusion that only the core is responsible for the success in overclocking the Celeron. Now the sweet thing about the Celeron is the fact that it’s using the Deschutes core, as already mentioned. This core was designed to run at least 333 Mhz as in the Pentium II 333. The 0.35 micron Klamath is already reaching 300 MHz without a problem, so that you can imagine that you will hardly find a Deschutes core that doesn’t at least do 333. These cores are used in a Celeron and the Celeron is specified to 266 MHz only to not damage the sales of the Pentium II 233, not because the core wouldn’t be fast enough. So here we are, Celeron is the number one overclocking CPU and if you should run it fast enough, you can even reach Pentium II 350 scores, particularly in 3D games as Quake II, but by paying less than a third for it. The problem for overclocking is that you will need a BX board that doesn’t detect the FSB clock automatically, so that you can run this baby at 100 MHz FSB.
The Celeron comes as naked as Andy created him (before he handed over). No plastic cartridge covers the PCB and the heatsink that comes with it has to be fixed in a slightly annoying procedure. Intel was trying at least a little to keep people from plugging Celeron into LX or BX boards. The little mounting brackets which fit nicely in any EX board wouldn’t fit at all into LX or BX boards. MSI is only one of the motherboard manufacturers who told me their plans on working around that. Until then you shouldn’t play football with your computer after plugging the Celeron in your LX or BX board, because you won’t be able to secure the Celeron in Slot 1. This is important for people in earth quake endangered areas.
There isn’t much more than the CPU core on the PCB of Celeron. Please note that you won’t find the R5/R6 resistors as in Deschutes for allowing it 100 MHz FSB officially. The Celeron is meant to be running at 66 MHz FSB only, so B21 is hardwired to Low.
There isn’t much to say, the back side of the Celeron is simply empty.
Note: ‘PCB’ stands for ‘printed circuit board’.
