Intel Pentium 4 2.4C Overclocking

by Ilya Gavrichenkov
06/04/2003 | 11:07 PM

Not so long ago Intel announced a few processor models that work with the new 800MHz bus. The remarkable thing about this announcement was the fact that it was devoted to CPUs working at not very high core frequencies, not the fastest and the most expensive ones. As a result, the functions, which used to be a distinguishing feature only of the flagship CPUs from Intel, are now supported by the less expensive processors.

 So, Intel’s 2.4GHz, 2.6GHz, 2.8GHz and 3.0GHz CPUs can all boast Hyper-Threading and 800MHz bus. The circuit, which has been implemented in every Pentium 4 die, is now brought to life. The Pentium 4 platform entered a new era!

The use of Hyper-Threading and 800MHz bus in platforms other than High-End ones is not the only interesting thing about this announcement. Overclockers have surely paid due attention to this event, because the coming of the new Pentium 4 family may imply the arrival of new heights to be reached by overclocking and tweaking. Junior Pentium 4 processors with the 800MHz bus evidently use the same core as their 3GHz fellows. Moreover, the upcoming Pentium 4 3.2GHz due in the end of this month is going to use this core, too.

As we see, all Pentium 4 processors intended for
800MHz bus use the same D1 core stepping.

This fact gives us some hope that the slower Pentium 4 CPUs with the 800MHz bus clocked at 2.4GHz can be speeded up to 3.2GHz and even more. With Hyper-Threading support, these CPUs may be used to build the today’s fastest systems. The only obstacle that may arise on the way to overclocking Pentium 4 2.4C is the necessity to overclock the bus, too. As the multiplier in Intel CPUs is fixed, you can only speed the CPU up by increasing the FSB frequency. But the standard frequency equal to 800MHz (200MHz FSB) is already pretty huge and has even required developing new chipsets. So, Pentium 4 overclocking may be limited by the bus rather than the CPU capabilities and make it impossible for the Pentium 4 supporting 800MHz bus to show high results. So, that’s going to be the topic of this review: whether these problems can be solved and how high the performance can grow if Intel Pentium 4 2.4C gets into skillful overclockers’ hands.

Getting Started: Overclocking Pentium 4 3.0

Before putting our hands on the 2.4GHz model, let’s first consider the overclocking potential of the top-end model of the Pentium 4 family with all its Hyper-Threading, 800MHz bus and 3GHz frequency.

So, soon after Intel’s announcement we hunted down a brand-new Pentium 4 3.0GHz, lassoed it and brought down into our dungeon (to the basement of our test lab). That’s what our trophy looks like:

As you see, it is a pretty ordinary, off-the-shelf specimen, caught in a regular shop. This processor has “SL6WK” S-Spec and, accordingly, features the new Northwood core with D1 stepping. This stepping is used in all Pentiums 4 supporting 800MHz bus (and sometimes in processors with 533MHz bus and disabled Hyper-Threading).

Let me remind you that D1 stepping processors feature “multiple VID”, which means that processors with the same S-Spec may have different core voltages. The Vcore is set by Intel on the packaging phase and depends on the quality of each given die. Of course, CPUs with lower voltages have higher overclocking potential. I had no choice, actually, and it happened that our Pentium 4 3.0 had “1.55V max” marking. It is the worst option as this is the highest possible voltage (there are Pentium 4 3.0 with 1.475V Vcore!). But let’s not get in despair.

The testbed we used for overclocking was based on the ASUS P4P800 Deluxe mainboard (the i865PE Springdale chipset). This mainboard (or chipset, if you like) supports 800MHz bus that is necessary for work (and overclocking!) of Pentium 4 3.0GHz. Besides, I had to spend some time finding the memory fast enough to match the CPU, so that they would work synchronously to achieve highest performance. The memory I used was PC3700 from OCZ. We didn’t adjust the cooling system and used the standard cooler. Also the testbed featured an ATI RADEON 9700 PRO based graphics card.

First, I set the FSB to 200MHz and started the system up in the regular mode. It worked! :) So, let’s rock and overclock. The multiplier of the CPU was fixed (what else could you expect from Intel?), so I sat down to raising the FSB frequency.

Step 1. Without raising the voltages, I set 220MHz FSB. The system woke up and worked without any problems. Well, that was nice. Let’ go to the next step…

Step 2. 230MHz FSB. Nothing changed. The system seemed to take no notice about what was going on. I congratulated myself with being rightly optimistic about the D1 core stepping: it did prove great. I achieved 230MHz frequency (x15 = 3.45GHz) without much effort and without even touching the Vcore! Having checked other websites for the overclocking results for earlier processors, I found that there had been few cases when anyone reached such a frequency. Moreover, they succeeded only with the help of extreme cooling or a huge voltage boost… But that’s not the end!

Step 3. Can the beast notch 240MHz FSB? I set the frequency in BIOS and the system didn’t load Windows XP up… But we have our trumps yet. I raised the voltage to 1.725V and Windows XP flew into the screen and worked without a squeak.

Summing up: I got a perfectly stable system that worked at 240MHz FSB, that is, with an effective (Quad Pumped) frequency of 960MHz! A simple calculation shows that the final CPU frequency equaled 3600MHz, which is not only an excellent result, but also a kind of record, considering the use of air-cooling only. And the core voltage was only increased to 1.725V.

So, now we know that the D1 core stepping offers a lot to an overclocker. But as you remember, we undertook our experiments with a top-end model. Of course, Intel usually picks up the best dies for its top-end CPUs, so we assume that the value CPUs won’t show us the same results. Or maybe they will? Let’s not make any more guesses, but just check it out.

Highlight of the Program: Overclocking Pentium 4 2.4C

Although we successfully overclocked a Pentium 4 3.0GHz to 3.6GHz using only air-cooling, we were not that satisfied. This processor is quite expensive and its overclocking is not so rewarding as that of low-end models. So, let’s go to the grass-roots: the slowest model of the Pentium 4 family with the 800MHz bus.

Let me introduce to you the actual hero of this review: Intel Pentium 4 2.4C processor. It is not just an ordinary Pentium 4 (the letter C after the frequency is not a slip of the tongue or typo), as it boasts significant innovations:

• Pentium 4 2.4C is intended for work with 800MHz bus. It means that it requires mainboards supporting 200MHz FSB. Such mainboards are those based on the new i875 and i865 chipsets and also – overclocker mainboards based on the old and time-tested i845PE. Thus, Pentium 4 2.4C has a fixed multiplier = 12x.
• Pentium 4 2.4C supports Hyper-Threading, which once was available only in top-end Pentium 4 CPUs. As you know, Hyper-Threading refers to a virtual multiprocessor system. One physical CPU is recognized by the system as two logical CPUs: it helps to load the processor’s computational units to the full and, as a result, to achieve a certain performance gain.
• By launching new processors supporting 800MHz bus, Intel announced its new approach to the CPU voltage formation. The company won’t set a fixed voltage, but will suggest a range of voltages. During the actual production stage all processors are divided into four classes. Each class has a certain voltage from 1.475 to 1.55V, depending on the die quality. Of course, models with the minimal core voltage are most interesting for overclockers as they have the highest speed-up potential. However, there is no marking on the processor telling its voltage, so you cannot know the voltage until you install the CPU into the mainboard.
• The last feature of Pentium 4 2.4C is the use of the new D1 core stepping, coming down from the top-end Pentium 4 processors. This stepping has F29h CPUID and is going to ensure good overclockability.

In fact, Pentium 4 2.4 with the C1 core stepping used to be good for overclocking, too. But there is something wrong about them now, as the last pieces produced do not please us with their overclocking potential any more. Still, Pentium 4 2.4C overclocking is a much more exciting procedure. Even if the 2.4C loses to the 2.4 in the frequency growth, it will beat it up in performance (Hyper-Threading and the 800MHz bus will do the job!).

But let’s turn from the theoretical talk to real life. This is our CPU:

It is an off-the-shelf Pentium 4 2.4C with 800MHz bus, D1 core stepping and SL6WF S-Spec. All available Pentium 4 2.4C processors have this S-Spec. I was unlucky with the Vcore once again. Our participant had the maximum possible Vcore: 1.55V. Still, the above-tested Pentium 4 3.0 had high Vcore, too, but did quite well at overclocking. A few words about the price: I bought Pentium 4 2.4C in an ordinary shop for about $180. I guess such pricing will make this CPU popular among overclockers.

Now, I’m rolling out my testbed:

• Intel Pentium 4 2.4C CPU;
• Boxed cooler;
• ASUS P4P800 Deluxe mainboard;
• OCZ PC3700 memory: two modules by 256MB;
• ATI RADEON 9700 PRO graphics card.

So, I installed the processor, set 250MHz FSB and turned the system on. It wouldn’t power up. The problem was simple: when testing Pentium 4 3.0, I made the memory work synchronously with the FSB. This time I forgot to change this setting and wanted the memory to work at 500MHz (250MHz DDR). Although it was PC3700, it wasn’t intended to work at 250MHz and it didn’t. So I browsed through the BIOS Setup and set the memory divisor to 4:5 from the FSB frequency. The i865PE chipset allows such things. In this case, when the FSB frequency is 250MHz, the memory is clocked at 208MHz, which is within its nominal specs. Of course, the system worked all right this time.

I composed a table listing the memory frequencies in systems with i875 and i865 chipsets when the FSB is overclocked:

After the system booted up at 250MHz FSB, I started to increase the FSB frequency steadily to find the highest summit our Pentium 4 2.4C could climb. At 275MHz FSB the processor worked without problems and without any additional Vcore increase. Unfortunately, this was all I could squeeze out of the thing. At 276MHz FSB, no voltage increase and no memory frequency reduction could make the CPU pass 3DMark2001. So, the result is:

The processor notched 3.3GHz, and the bus – 1100MHz. What’s important, I achieved this without voltage tweaking. That is, such overclocking is quite safe as far as processor health is concerned. Overclocking without any voltage increase doesn’t reduce the life term of a semiconductor die. As for the memory, its frequency grew to 440MHz with the 4:5 divisor:

Our respect to OCZ and its PC3700 modules, which allowed us to achieve this high result. By the way, we could make the same thing using Low Latency PC3200 modules from Corsair.

Accordingly, the peak bandwidth of the dual-channel memory system in this mode reaches 7.0GB/s, which is astonishingly high. That’s what it gives us in practice:

To our regret, we couldn’t overclock our Pentium 4 2.4C to 3.6GHz as we did with Pentium 4 3.0. Still, 3.3GHz is a good result. This is higher than the frequency of the upcoming top model of the Northwood-based Pentium 4 family. Moreover, I want to say once again that I achieved this using a standard air cooler and without any Vcore increase. In other words, anyone can do the same thing with the help of the most primitive methods, which don’t tell negatively on the system’s health.

Performance

Now, let’s see how speedy the overclocked Pentium 4 2.4C is, compared to top-end models from the Pentium 4 and Athlon XP families. We used the following testbeds:

All the tests were run in Windows XP SP1.

Well, let’s start with Winstone tests.

Athlons are traditionally strong in Business Winstone 2002 and Athlon XP 3200+ is on top here. But the situation changes in Content Creation Winstone 2003: the 1.1GHz bus together with the 3.3GHz CPU frequency are weighty arguments.

The synthetic PCMark2002 shows another strong point of the platform based on the overclocked Pentium 4, besides the high CPU performance. It is the high bandwidth of the bus between the CPU and the memory. Although we couldn’t use the FSB and memory in synchronous mode during overclocking, the Pentium 4 2.4C system is the fastest.

In streaming data encoding tests and during data compression the overclocked bus and CPU core bring Pentium 4 2.4C above the “normal” rivals at encoding streaming data and archiving.

Now come gaming tests:

The same is true for 3DMark tests: the overclocked Pentium 4 2.4C is the best.

Again, Pentium 4 clocked at 3.3GHz proves very fast in gaming applications. It is defeated by Athlon XP 3200+ only in Unreal Tournament 2003 tests where Athlon XP CPUs are traditionally strong.

And in conclusion, professional applications:

It’s useless to compete with the overclocked Pentium 4 2.4C in rendering speed. Hyper-Threading technology support allows this CPU to run really fast here.

Still, the high performance of one application is not the main advantage of Hyper-Threading. The most important thing is that you can run a few applications simultaneously and they will not disturb one another. For example, I turned on video capturing on the testbed and at the same time played Serious Sam 2. Hyper-Threading did its job well: the game ran smoothly and there were no dropped frames during the video capture running in parallel. When I tried to do the same on the Athlon XP 3200+ based system, I got 30% of all frames missing and the game was far from playable.

Overall, whatever AMD fans may say, Hyper-Threading is a tricky, but useful thing, and I consider it an advantage that the slower Pentium 4 CPU models have it now.

Conclusion

So, the low-end model of the renewed Pentium 4 series, Pentium 4 2.4C with the 800MHz bus and Hyper-Threading support, is a real bargain for overclockers. Counting out about $180 for the CPU and $120 for the mainboard, you get the fastest system without any big risk or much effort. Of course, the history chronicles better overclockability in a relative measure, but from the point of view of getting the fastest system at the lowest price Pentium 4 2.4C stands unrivalled today.

At the same time we should note that the arrival of overclockable Pentium 4 2.4C CPUs doesn’t mean the end of the Athlon XP 1700+ overclocking epoch. Low-end models from AMD are much cheaper and will surely remain the best choice for overclockers with a small financial budget.