Verdict: AMD's new budget wonder-chip
Just when you thought the Athlon 64 market couldn't get any more confusing, with the multiple sockets, chip designs and sometimes misleading PR ratings, along comes Sempron.
Sempron is being launched on two platforms, Socket A and Socket 754. The Socket A version is nothing but a Thoroughbred core Athlon XP, so there's nothing really new about it.
The chip of interest is on the Socket 754 platform, which was originally designed to host the Athlon 64. Unlike Socket 939 CPUs, Socket 754 CPUs only support single-channel memory, but have the huge advantage of a wide range of excellent motherboards starting at just £55.
Sempron is to the Athlon 64 what the Duron was to Athlon XP - a striped-down, low-cost little brother. The chip itself is a crippled Newcastle core Athlon 64, with no 64-bit support and only 256KB of Level 2 cache. For comparison, Newcastles have 512KB of Level 2 cache, and Clawhammers have 1MB. Almost all Semprons will be CG stepping chips, which is the latest stepping of any Socket 754 CPU.
The smaller Level 2 cache and low core voltage of 1.4V means Sempron outputs much less heat than Athlon 64, and so it has excellent overclocking potential. Sempron is being launched as a 3100+, running at 1.8GHz with an FSB of 200MHz. Considering a Newcastle-core Athlon 64 2800+ runs at 1.8GHz as well, the rating system seems a little odd. This is because the Sempron model numbers are based on performance in productivity apps instead of multimedia/3D apps, as in Athlon 64.
Overclocking on the Socket 754 platform was a tough job until recently, due to the lack of functioning AGP and PCI locks. But now that the Nvidia nForce3 250Gb and VIA K8T800 Pro chipsets have finally hit the market, overclocking has become a real possibility.
The board we used for testing was the Abit KV8 Pro. Abit is, of course, renowned for producing excellent boards for overclocking and this one is no exception, although at first we couldn't even get the board to POST with a Sempron inserted. So we popped in one of our Athlon 64 chips and upgraded the BIOS to support Sempron. If you're ordering a new motherboard, be aware that it may not support Sempron without a similar upgrade.
Performance-wise, the Sempron 3100+ is a very pleasant surprise. Despite the reduction in Level 2 cache size, there's really only a 2 per cent performance difference, compared to an Athlon 64 2800+, its nearest competitor. Even when compared to a Clawhammer-core Athlon 64 with 1MB of cache there's only a 6 per cent performance difference between them. In most applications the difference is less than this, and in modern games it's the graphics card that usually limits the frame rate, not the CPU.
The Sempron 3100+ is also a superb overclocker, as we easily boosted it to 2.43GHz by upping the FSB from 220MHz to 270MHz. All we had to do was increase the CPU voltage to 1.575V. This huge overclock was achieved using a fairly standard Akasa HSF, and even then the CPU temperature was still under control. What's most surprising is that the chip could easily go further, but the motherboard wouldn't benchmark stably above 270MHz. A voltage mod to the Northbridge may be all that prevented us from achieving a 300MHz FSB in order to get the CPU running at 2.7GHz.
CONCLUSION
As the performance difference between different Socket 754 chips at the same frequency is so negligible, you're left with two issues: price and 64-bit support. The nearest chip, both in price and performance, is the Athlon 64 2800+, and it costs only £10 more than the Sempron 3100+. This is certainly not a price difference to get excited about, so we
would like to have seen the Sempron 3100+ priced a little lower. At the moment, 64-bit software support is very limited and we don't envision a huge change in this situation until next year. But the £10 that you save by buying a Sempron 3100+ could be put to a better use on a motherboard with more overclocking options. Finally, you have to ask yourself how it compares to Intel's Celeron. Judging by our CPU Labs test earlier this year, there's no competition - the Sempron 3100+ would wipe the floor with Celeron.
The Sempron 3100+ is the new budget super-chip and we heartily recommend it.
