The processor is still crippled by the TLB bug

Dec 19, 2007 16:50 GMT  ·  By

AMD have just announced that they have released their special edition of the Phenom 9600+ quad-core processor, known as the "Black Edition". This version has the same features as the original Phenom 9600+, but provides full access to the clock multiplier.

The special edition has the same price as the standard one but is dedicated to overclocking enthusiasts that want to squeeze every CPU cycle from their processor. Unlike the standard Phenom 9600+, the clock multiplier is unlocked and users can easily tamper with the clock speed settings directly from the machine's BIOS in order to achieve higher clock speeds.

The operation requires special and expensive cooling solutions, as the processor radiates large amounts of heat when overclocked. AMD gave full access to the clock multiplier but that does not mean that the chip manufacturer encourages overclocking. The package reads that "AMD is not responsible for damages caused by overclocking (even when overclocking is enabled with AMD Overdrive(tm) software)".

Not long ago, there have been reports that all the Phenoms and Barcelonas are crippled by a TLB (translation lookaside buffer) erratum that renders the computer inoperable when the processor is working at full load. This is the result of a race condition that occurs when two arbiters attempt at writing the same blocks of information following the same set of rules.

AMD issued two workarounds that are supposed to fix this glitch, but at a great compromise in performance. Practically, the CPU frequency is kept below 2.2 GHz to prevent it from running at full speed. That is why things are looking quite confusing: since the erratum surfaces when the CPU crosses the safe 2.2GHz limit, why sell a processor that can go above the limit? The standard Phenom 9600+ already operates at 2.3 GHz and the overclocked version will jump the 2.6 GHz barrier, so why bother?

AMD states that the bug has not been observed in any production installations. The AMD engineers "invoked" it during their internal stress tests which push the cores to the limits in various operations. The company ensures that average users will rarely bump into the TLB erratum, but is it worth taking the chance?