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AMD Athlon X2 3600+

The First 65 nm Glimpse

by Josh Walrath

The X2 3600+ and AM2

            The X2 3600+ is a bit of an odd bird for AMD, but we will start to see its type be more common from here on out.  AMD used to not support half multipliers, such as 8.5, 9.5, etc. but with the new series of chips they are utilizing that type of system.  Instead of having two chips at identical clock speeds differing only with L2 cache size, AMD has now standardized the L2 cache size on its desktop 65 nm parts to 512 KB and the different models are 100 MHz apart.  So the 3600+ is clocked at 1.9 GHz, the 3800+ is at 2.0 GHz, the 4000+ is at 2.1 GHz and it goes on from there.  We still see the 90 nm parts feature both 512 KB and 1 MB of L2 cache per core, but once 65 nm becomes the standard we will eventually see those parts recede.

            There will be no 65 nm parts for the now discontinued socket 939, instead all parts will push the AM2 socket and DDR-2.  The move to DDR-2 has been controversial to say the least.  Many users complain that there was no reason to move from DDR, but I do not necessarily share that view.  There are many design advantages for DDR-2 over DDR, but they are advantages that are more focused on manufacturers vs. end users.  AMD hit about the perfect time for DDR-2, as it had matured quite nicely and the overall latency increase that DDR-2 suffered was nicely masked by the massive amounts of bandwidth DDR-2 800 provided.  Not to mention that the 200 MHz core memory speed now matched the 200 MHz core that PC3200 DIMMS featured.

            The other benefits of DDR-2 are on-die termination, smaller geometries in production so greater density per chip is achieved, and the lower voltage that these DIMMS require for operation at high speeds.  In dual channel applications with DDR-2 800 DIMMS, a theoretical maximum of 12.8 GB/sec can be achieved.  So far we have not seen anywhere near that and only some of the fastest dual channel DDR-2 800 on fast Athlon X2 64s have scores hitting around 8 GB/sec.  It can be argued that no AMD Athlon 64 X2 chip can actually utilize the 12 GB/sec of bandwidth afforded by these DIMMS, but my feeling here is that AMD had an eye on the future when they transitioned to DDR-2 when they did.  It was a necessary move for AMD to keep up with the industry, but they also knew that they needed to build an infrastructure that will support the next generation of dual core and quad core chips waiting to hit this upcoming summer that will more effectively utilize the bandwidth of DDR-2 800.

            The selling point that AMD is perhaps most excited about is that of power usage.  These new 65 nm dual core chips are rated at a maximum of 65 watts TDP.  This is the absolute worst case scenario for these chips, running at 100% with a monkey on their back brandishing a barbed whip.  AMD applies this 65 watt value to all the 65 nm X2’s from the 3600 to 4800.  This means that the lowest member of the group could potentially eat up even less wattage than its faster clocked siblings.  AMD claims a slightly better performance per watt figure for their 65 nm X2’s than the competing Intel Core 2 Duo.  And according to the work done by Dr. Michael Schutte, AMD has more than a leg to stand on.  According to his tests a 4800+ (2.5 GHz) was consuming about 41 watts at 100% utilization of both cores.  Perhaps even more impressive is the low 8.8 watts consumption at idle.

            AMD still has a lot of work to do on its 65 nm process before they are done with it, but AMD has a philosophy of continual improvement over time.  The 90 nm process we see today is significantly improved in both performance and power usage than when AMD initially introduced it with the Winchester cores.  We can expect this same kind of gradual improvement over time until AMD is ready to start production on their 45 nm process.

Next:  The Setup

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