The AMD Phenom has hardly had an auspicious start. We were shocked when we learned the release clock frequency would be a lowly 2.3GHz. But then it turned out this was partly caused by a specific problem with the revision of the processor design available at launch.

Now a fixed version looks set for April. Will this provide the boost that AMD's Phenom so desperately needs?

TLB problem - TLC needed

According to AMD, its reasons for holding back the expected 2.4GHz spin of the Phenom at launch was due to a problem with the Translation Lookaside Buffer (TLB), although there are numerous conflicting statements from the company about this.

The TLB is part of the Level 3 cache logic - a key element of the Phenom's design. The TLB deficiency wasn't expected to cause instability very often, but clearly it would be frequent enough for some concern.

Originally, AMD stated that this problem only affected Opterons, but now it has become clear that all Barcelona-core processors up to and including stepping B2 have the issue, also known as 'Errata 298'. All processors have errata, which BIOS tweaks, microcode updates or even operating system software patches can counteract.

In the case of AMD's TLB problem, a BIOS update has been able to prevent the instability. However, the BIOS fix also has a downside. It causes a substantial performance hit, with AMD itself quoting this as 'around 10 per cent', and some putting the deficit at as much as 20 per cent with some applications.

AMD's B3 stepping

This is where the B3 stepping comes in. The new revision of the Barcelona core includes a microcode update to fix the TLB issue. So these new chips won't incur the performance hit of earlier versions. When AMD needs every per cent of extra speed it can get, this is very good news.

Quite how the TLB problem caused the delay to the 2.4GHz Phenom, which is still on pre-order on most websites, remains a little unclear. It isn't because the TLB issue directly prevents higher frequencies, but appears to be because AMD is waiting for the B3 stepping before release. So everything from Phenom 9700 upwards will be the new B3, and the current chips will be replaced with it too.