| CPU Speed | FSB Speed | Clock Multiplier |
| 233 MHz * | 66 MHz | 3.5x |
| 266 MHz * | 66 MHz | 4.0x |
| 300 MHz * | 66 MHz | 4.5x |
| 333 MHz * | 66 MHz | 5.0x |
| 350 MHz | 100 MHz | 3.5x |
| 400 MHz | 100 MHz | 4.0x |
| 450 MHz | 100 MHz | 4.5x |
* Applicable for Celeron also
Optimal Speed for Your CPU : Remember, just because your neighbor or brother or whoever can achieve a certain speed with their identical CPU doesn't mean that yours should be able to hit that same level. Each and every CPU is unique. Considering these small cores have 8 million trace routes, it should come as no surprise that no two CPU cores behave the same under stress
Intel Pentium II 233 - 300 Core Codename Klamath
Intel's first Pentium II CPU had the codename 'Klamath' and are 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. 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.
The Klamath is certainly overclockable, but in most cases it requires the increase of the front side bus frequency (external bus speed), 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 overclocker you've got to live with the fact that your system can crash any time. 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.
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 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.
There is a serious difference between 333 and 350 MHz Pentium II CPUs and its brother at 400 MHz and above. The 400 MHz version has got faster L2 cache modules. Another major difference is the timing of the L2 cache. 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.
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 mostly 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. 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 behavior and can easily be the reason for system crashes. The Level 2 cache, which operates at approximately one half the speed of the CPU, is matched by Intel to the speed of the CPU core to which it is connected. There's usually a good deal of leeway, but the individual speed of your cache is a key limiting factor in overclocking your CPU. AAH!!!
I consider everyone as really irresponsible, who runs his business software on a system with a highly overclocked 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 :- 350/100 3.5 inner multiplier and 100 MHz FSB (requires motherboard that let's you choose 100 MHz FSB)
Pentium II 350 :- 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. Reaching higher speeds safely only works with special 7 ns SDRAM modules and a special cooling system.
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 newer successor have an internal L2 cache and hence will be more sensitive to higher clock speeds as well. This 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 !! naked !! as Intel created it. 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. Until then you shouldn't play cricket 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
The goal of overclocking is to find your CPU's comfort zone--the speed at which it will run reliably, without system errors or data corruption. Here are some common, relatively conservative settings.
Pentium IIs With Default 66 MHz FSB (233 MHz to 333 MHz)
| Over clocked Speed | Clock Multiplier | FSB Speed | Chipset |
| 300 MHz | 4.0 | 75 MHz | 440LX |
| 300 MHz | 3.0 | 100 MHz | 440BX |
| 336 MHz | 3.0 | 112 MHz | 440BX |
300-MHz Pentium II
| Over clocked Speed | Clock Multiplier | FSB Speed | Chipset |
| 338 MHz | 4.5 | 75 MHz | 440LX |
| 350 MHz | 3.5 | 100 MHz | 440BX |
| 392 MHz | 3.5 | 112 MHz | 440BX |
| 400 MHz | 4.0 | 100 MHz | 440BX |
333-MHz Pentium II
| Over clocked Speed | Clock Multiplier | FSB Speed | Chipset |
| 350 MHz | 3.5 | 100 MHz | 440BX |
| 375 MHz | 5.0 | 75 MHz | 440BX |
| 392 MHz | 3.5 | 112 MHz | 440BX |
| 400 MHz | 4.0 | 100 MHz | 440BX |
Note: To run reliably at a 100-MHz FSB, you need to have 100-MHz SDRAM installed in your system. Also note that in many of the cases listed above, increasing the FSB speed requires you to lower the clock multiplier on your system.
Pentium IIs With Default 100-MHz FSB (350 MHz to 450 MHz) Since August 1998, Intel has been locking the clock multiplier on its CPUs, so it probably will not be possible to change the multiplier when overclocking a 350-MHz, 400-MHz, or 450-MHz Pentium II. If you try, the CPU will either refuse to boot the machine, or it will boot it up at 1/3 its proper speed. To get around this limitation, a Pentium II overclocker's only remaining option is to increase the speed of the frontside bus.
350 MHz (and above) Pentium II
| Default Clock Speed | Default Clock Multiplier | |||
| Over clocked Speed | FSB Speed | Overclocked | CPU Speed | |
| 350 MHz | 3.5 x | 112 MHz | 392 MHz | |
| 400 MHz | 4x | 112 MHz | 448 MHz | |
| 450 MHz | 4.5x | 112 MHz | 504 MHz | |
No comments:
Post a Comment