AMD considers the quad core Phenoms to be the first true quad core design, as these processors are a monolithic multi-core design (all cores on the same piece of silicon die), unlike Intel's Core 2 Quad series which are a multi-chip module (MCM) design. The processors are on the Socket AM2+ platform.
Before Phenom's original release, a flaw was discovered in the translation lookaside buffer (TLB) that could cause a system lock-up in rare circumstances. Phenom processors up to and including stepping B2 and BA are affected by this bug. BIOS and software workarounds disable the TLB, and typically incur a performance penalty of at least 10%. This penalty was not accounted for in pre-release previews of Phenom, hence the performance of early Phenoms delivered to customers is expected to be less than the preview benchmarks.
Source [Wikipedia]
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