Apparantly the last of the K6-2 model Microprocessors, AMD's release of the 400MHz CPU has been met with both excitement as well as casual disinterest.
News of impending release of the K6-3, and the early availability of socket 370 Celerons have created a standoffish attitude in a large percentage of the upgrade market. We all seem to be standing around waiting to see which platform next aligns itself as the guide-on bearer of the high speed low-cost processor market.
These final K6-2s like their predecessors, boast support for AMD's 3DNow! instruction set designed to improve 3D graphics and multimedia performance, and a full 64KB of L1 cache. Availing myself of the purchase of some new processors I recently obtained both 380 & 400MHz parts and while there are some 380MHz parts available with the original core, both of the parts had the code number "26351" impressed directly onto the ceramic casing of the CPU indicating that both parts had new XT cores.
These K6-2s new higher frequency models or steppings as they are referred to in the semiconductor industry, are labeled as as Model 8/[F:8] in documentation to indicate the use of AMD's new XT core, while the original K6-2 core is documented as Model 8/[7:0].
Beating The Clock According to AMD's specifications, the K6-2 XT core translates the original core's 2.0x clock multiplier into a 6.0x clock multiplier, indicating that the original core supports clock multipliers ranging from 2.0x - 5.5x, while the XT core supports clock multipliers ranging from 2.5x - 6.0x, with the 2.0x setting corresponding to a 6.0x clock multiplier.
State of BF[2:0] Inputs Processor-Clock to Bus-Clock Ratio. The ratio selected is dependent on the stepping of the Model 8. The 2.0x ratio is supported on the Model 8/[7:0] (original core design), whereas the 6.0x ratio is supported on the Model 8/[F:8](XT core).
This expresses the the processor's ability to perform at it's rated frequency even without higher speed frontside bus support (i.e. 66MHz x 6.0 = 400MHz).
The XT core architecture has also made some interesting changes in the Write Handling Control Register, providing changes in the Write Merge Buffer and a wider Write Allocate Limiter that allows the processor to cache a larger memory write that isn't already located within the L1 data cache.
Using a burst read to prefetch data located outside the L1 cache, a "Write Allocate" stores the data from the memory write in the processor's L1 data cache. The performance of a single write allocate function is no greater than if the data were written to memory unless the burst read takes place, the real performance edge of write allocate appears in writes to the write allocated cache line following the initial write allocate.
Turn Up The Air Conditioner The 380 & 400MHz K6-2s differ in their tolerance for operating case temperatures under maximum thermal power. Where the AMD-K6-2/380AFR CPUs allow for an ambient case temperature in the 0°C-70°C range, the AMD-K6-2/400AFQ part requires an ambient case temperature 0°C-60°C in range. This is indicated by the Q in the part number's suffix.
Since the K6-2 400MHz CPU's release back in Nov. many of the super7 mainboard manufacturers have released BIOS upgrades that will allow you to take advantage of the processor's enhanced write allocate features. You'll need to upgrade even if your BIOS appears to correctly identify the CPU on your boot screen. While the processor will work without the BIOS update, your performance can suffer - falling to a level slightly lower than the capabilities of the K6-2 350MHz.
Performance - The K6-2 400MHz processor overclocks about as well as I expected it to, easily reaching the 450MHz frequency on a 100MHs FSB and increasing the FSB to 112MHz, performed well at 4.0 clock cycles.
At present the price/performance ratio for both of these processors is quite outstanding with the K6-2 400 in the $160.00 range. At these prices you can afford to upgrade more than just the processor - increasing system RAM or even a new high-performance graphics adapter.
While I wouldn't recommend the upgrade for present owners of K6-2 333/350MHz models, the increase in performance is significant enough to warrant the upgrade for K6-2 300MHz owners. If you are a power gamer, you may however deem it wise to wait for the "Sharptooth" (K6-3), which is most likely to be released in Feb. but at +$100.00 the cost. Otherwise, both processors are low-cost high performance components that will meet even the most stringent of requirements for the average user.
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