X-bit labs

AMD Athlon 64 3800+ CPU: E3 Processor Core aka Venice at the Door (page 3)

Category: CPU

by Ilya Gavrichenkov

[ 04/03/2005 | 04:06 PM ]

Enhanced Integrated Memory Controller

Every time a new Athlon 64 processor core come out AMD engineers continue tuning up their integrated memory controller. Note that this is done not only for the sake of increasing the processor performance, but mostly in order to extend the compatibility of this memory controller with the different DIMM modules and their configurations. The previous 90nm Athlon 64 processor core aka Winchester had certain performance limitations when four DDR400 SDRAM modules were used. If there were four single-side DDR400 SDRAM DIMMs installed in a system with a Winchester based Athlon 64 CPU, they could only work with the 2T timing, which caused a few percent drop below the usual performance level. If there were four double-side memory modules installed, DDR400 SDRAM would not work at all and its working frequency would automatically drop down to 333MHz.

AMD engineers promised to eliminate this problem in the new Venice core and they did keep their word. Athlon 64 processors based on Venice can work with four single-side DDR400 SDRAM modules without any limitations, and if there are double-side DDR400 SDRAM DIMMs installed, they can work at 400MHz with 2T timing.

Besides wider compatibility of the Venice’s memory controller, it also got noticeably faster. Among the tweaks implemented in Venice we should definitely point out enhanced hardware data prefetch and more write combining buffers (4 instead of 2).

All these improvements should help Venice based Athlon 64 processor to outperform their counterparts based on the older core revisions but working at the same clock frequency. And the performance gain will be more noticeable if there are four memory modules installed in the system.

Model Line-Up

The new 90nm Venice core will let AMD update the entire Socket 939 Athlon 64 processor family. If the previous Winchester core was only used for CPUs working at up to 2.2GHz core clock, then Venice should definitely help improve this situation. AMD starts shipping Socket 939 Athlon 64 on Venice core with performance rating from 3000+ to 3800+ on April 4. Note that the 3000+, 3200+ and 3500+ CPU models will replace the corresponding models on Winchester core, and the new Athlon 64 3800+ will replace the corresponding solution on Newcastle core.

The total core replacement will also include Athlon 64 4000+, which is now based on ClawHammer core with 1MB L2 cache. On April 15 AMD will begin shipping new Athlon 64 4000+ processors on San Diego core, which will be the same as Venice but with larger L2 cache memory. Summing up everything we have just said, we would like to offer you a table listing all Socket 939 Athlon 64 processors based on the old and new processor cores, which are already available or will become available shortly:

As we see, Venice based CPU prepared one more surprise for us: variable Vcore. AMD resorted to the same trick Intel did when packaging their CPU dies. Venice based processors will not have Vcore indicated on the die package. Different CPUs may have different Vcore: 1.35V or 1.4V. And unfortunately, there will be no way to tell the nominal processor core voltage from its exterior. As for the thermal design power, the new Venice core seems to have the same heat dissipation characteristics as the previous cores at first glance. However, in reality things are not quite like that. The thing is that Venice has somewhat bigger frequency potential for the allowed heat dissipation limited by the thermal design power. The new Athlon 64 on Venice core working at 2.6GHz frequency will feature 89W typical heat dissipation, while the next stage of heat dissipation, 104W, will only be reached when the working frequency rises to 2.80GHz, if at all.

In conclusion I would like to mention that despite all these changes made to the Venice core, it retained the same die size and number of transistors as Winchester core.