You may or may not have noticed that we've yet to dedicate a review to AMD's Phenom CPUs. This is for a number of reasons but mainly the lacklustre performance of the first batch of CPUs combined with the fact that our initial samples weren't available at retail and were actually engineering samples with slightly different configurations, meant we never found a slot in our schedule that seemed appropriate.
A few months later, though, and we've received a CPU you can actually buy in the shops, in the form of the 9600 Black Edition, and we also have retail motherboards with mature BIOSes on which to test it. So, finally we can give Phenom a fair test and see if this much maligned CPU is a worthwhile purchase for those who require a bit more oomph than dual or single core CPUs can provide.
Being our first look at these new CPUs, we'll briefly cover the technology that powers them and compare it to the way Intel does things with its Core 2 Quad CPUs. After that we will move onto performance comparisons where we'll see if all the technology actually makes for a CPU that's faster in the real world.
We'll start with the basics. All Phenoms will work with existing AM2 motherboards (assuming a BIOS update is available) so if you've stuck with the green team over the last year or two, buying a Phenom shouldn't require you to upgrade the rest of your system. However, if you do use one of the newer 700-series boards that have AM2+ sockets, you will be able to take advantage of the more sophisticated power saving features whereby the voltage and clock speed of each CPU core can be changed depending on how much the core is being used.
Also, AM2+ boards now use a faster 2GHz hyper transport (HT) link between the CPU and memory controller so theoretically the CPU will run faster on these newer boards. We have a suspicion that the impact of reducing the HT speed to 1GHZ, by running a Phenom in an AM2 board, would actually be fairly minimal but we haven't checked whether this is the case, so feel free to report back your findings.
The execution component that sits at the heart of each core is largely the same as that used by the Athlon series of chips but with a number of tweaks here and there. For instance, SSE4 instructions are now supported and general SSE performance has also been improved, which should speed up games and other multimedia applications. There's also improved hardware support for virtualization, a common technique for simultaneously running two operating systems on one PC.
The on-die cache configuration has also changed with the addition of an extra shared layer known as L3. On-die cache memory is used to provide small very fast chunks of memory for the processor to access before it goes through the relatively lengthy process of retrieving data from main system memory. Finding the right balance of size and speed of cache can make all the difference to a CPU's performance.
For Phenom, the first 'layer' of memory is just 128kB per core, but it's very quick to access, the next layer (L2) is a more reasonable 512kB per core, but it takes more time to access. L3 is 2MB in size but this is shared between all four cores and takes even longer to access. This is in contrast to Intel's quad-core CPUs that don't use any L3 cache but instead have very large 8MB or 12MB L2 caches. The reason Phenom uses much smaller amounts of cache is because it includes an integrated memory controller that can communicate with memory much faster than Intel's chips, so it simply doesn't need as much.