The AMD Phenom X4 is AMD's first quad core processor line, based on the same 65nm process used for earlier Brisbane chips. Introduced in November 2007 the line suffered a massive setback when an issue was found within the chip's buffer which could cause system lockups in rare occasions. While patchable, this fix incurred an undesireable 10% performance penalty, and led to poor sales and negative publicity.
Once fixed, the line was relaunched, carrying a new naming model. Important destinctions between AMD's quad core design and Intel's include AMD's implimentation of an L3 cache (generally 2MB of cache shared between all 4 cores) and an on-chip memmory controller, a component still found within the northbridge on Intel platforms.
Today the line continues to lag behind Intel's offerings, causing great distress for the company management and shareholders alike.