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LOSTCIRCUITS	SHORTCUTS: A Process Shift Brisbane by Numbers Test Configurations Memory Subsystem Power Consumption 3D Rendering and Power per Renderpass POV-Ray- Cinebench AV-Encoding 3Dmark'06 F.E.A.R. DOOM3 FarCry L2 Cache Latencies The Plot Thickens Final Thoughts Give Us Some Feedback on this Review
AMD's Brisbane Core - the Transition to 65 nm And the cache latency
(Author: MS, January 5, 2007)

Brisbane by Numbers: New 65nm AMD Athlon 64 X2 Processor Tech Specs

Half-Dividers and Memory Frequencies

The base frequency of the external clock is - at least at this point - 200 MHz, however, the above table shows core frequencies of 2100 MHz, 2300 MHz and 2500 MHz, and only the top model a.k.a. X2 5000+ runs at 2600 MHz which can be divided by 200 MHz. All other models see the return of the so-called "half-multipliers", 10.5, 11.5 and 12.5x. Moreover, since the memory bus frequency is derived by an integer divisor of the CPU's core frequency, we are looking at some rather odd memory clocks. As a rule of thumb, the memory clock can never be higher than the "standard" frequency. In the case of a 2.4 GHz processor, the math is simple enough, for a DDR2-800 memory frequency, the core frequency is divided by 6 for a 400 MHz memory clock and an 800 MHz data rate. At 2500 MHz, things are getting a bit more complicated, if the same 1/6 divider is applied, the memory frequency increases to 417 MHz or 833 MHz data rate, which is above any specifications of DDR2-800. For compliance with the commodity market, the memory frequency, therefore, needs to be scaled down BELOW 800 MHz, but in absence of an independent clock, the only way to do this is to increase the divider to the next integer value. In this case it is a 1/7 divider and the memory frequency drops to 357 MHz or DDR2-714. Keep in mind that bandwidth is not necessarily a problem for the processors, in fact, it is hard to fin any application that even shows a difference between single channel and dual channel operation.

For those worried about raw bandwidth, we have plotted the different speed grades and their SiSoft Sandra "buffered" memory bandwidth.

The numbers tell a difference but the graphs show in the grand picture that the different speed steps are not that far apart from each other. There is more to a new CPU than just Sandra's memory bandwidth and on the pages to follow we have a cornucopia of benchmarks where we are comparing the 4800+ to the rest of the world. To make things more interesting, we will aso clock it down to a 2.4GHz core frequency and show a direct comparison to the 4600+ running at the same speed and under otherwise identical conditions.

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