It has been a long time since both Intel and AMD released value processor lines with so much promise. Both the Celeron D and Sempron (Socket 754) models are variants of popular high-end core designs, and not only provide a nice performance increase over last-generation designs, but look to have serious overclocking potential. The Celeron D's Prescott core should open a few eyes, as the Pentium 4 models run up to 3.4 GHz on Socket 478. The Sempron 3100+ features a 1.8 GHz clock speed, while the Athlon 64 3700+ checks in at a whopping 2.4 GHz. Whether this is the return of the value overclocking demons or just a tease is a question we'd like to answer, and have pitted the Celeron D 335 up against the Sempron 3100+ in a no-holds-barred overclocking competition.
The new Intel Celeron D processors use a variant of the Prescott core, only with a smaller L2 cache and a lower bus speed. The Celeron D includes a 256K L2 cache (compared to 1-MB for the Pentium 4) and runs on a 533 MHz processor bus (800 MHz for the Pentium 4). This allows Intel to offer the Celeron D at high clock speeds and low prices, while not affecting sales on the higher-end Pentium 4 line. The Celeron D 335 used in this article is clocked at 2.8 GHz, and its default performance is significantly lower than a comparable Pentium 4-2.8E.
The Sempron 3100+ is based on the AMD Newcastle core, and instead of 512K of L2 cache it has been cut in half to 256K. This is a bit better trade-off than the Celeron D to Pentium 4 comparison, but keep in mind that the original Athlon 64 core design featured a full 1-MB of L2 cache. The rest of the design specifications are consistent, and the Sempron 3100+ features an integrated memory controller capable of up-to DDR400 speeds, and uses a 200 MHz/1.6 GHz processor bus. The Sempron 3100+ runs at a 1.8 GHz default clock speed, and has very impressive performance for the class.
When overclocking the Sempron 3100+ and Celeron D 335, we took a very real-world approach to the process. This meant taking all possible scenarios into account, and ensuring we took into consideration the stability and heat of the overclocked CPUs, as well as overall platform characteristics and features. As we'll see later on, these did have a very real impact on both the overclocking speeds we attained, as well as the memory, system and CPU speeds attained.
The Celeron D 335 is a very standard overclock, due mostly to the AGP and PCI bus locking features present in the mainstream i865G and i865PE chipsets. This allowed us to go to the absolute limit in terms of overall clock speeds, while maintaining 66 MHz AGP and 33 MHz PCI speeds. This also meant not worrying about exceeding the AGP or PCI specifications of our peripherals, and ensuring that the Celeron D 335 was not held back in any way. After extensive testing, we arrived at a 100% stable overclock of 3.55 GHz using a 169 MHz front-side bus speed and a core voltage level of 1.45V. We were able to hit 3.6 GHz, but this didn't prove to be totally stable in long-term, rigorous testing.
The Sempron 3100+ is a tougher processor to overclock, because the popular K8T800 does not feature an AGP/PCI bus locking mechanism. We had some high hopes for the Sempron core, with the promise of 2.2-2.3 GHz at a minimum. Unfortunately, the highest speed our system could handle was 2.15 GHz, at a 239 MHz bus and a 1.475V core voltage. Once we moved into the 80+ MHz AGP/40+ MHz PCI speed range, system errors started cropping up.
By disabling and changing up various AGP and PCI components, we were able to go to 2.2 GHz, so the lack of AGP and PCI locking really was the culprit. We would have liked to use an nForce3 150 board (with locking capabilities), but none of our available units were Sempron-certified with a fully compatible BIOS. Of course, this scenario does have the advantage of higher system bus speeds, as well as slightly higher DDR speeds. The DDR divider was set at 412 MHz, to make sure we were keeping a value outlook, and not pushing the limits of standard PC3200 DDR.