[nilsbunger]

This was in Intel's dark days of P4 / "Netburst" microarchitecture. They goosed lots of GHz out of the chip by going with a very deep pipeline, but performance in real-world applications was terrible. (deep processor pipelines kill you when you mispredict a branch).

I sat in on a few sales calls from Intel about their new Pentium M / "Centrino" mobile architecture in 2003. What was amazing was that their performance graphs showed that Centrino had all the performance of P4, but with much lower power.

Basically, the terrible P4 microarchitecture, plus Intel's incompatible 64-bit approach (Itanium, aka "the Itanic"), left a big hole in the market where AMD stepped in and mopped up for 3-4 years with Opterons, the first 64-bit x86 processors.

Even today, x64 architecture is called "AMD64" for this reason -- AMD defined the instruction set, and Intel had to follow (for once).

IPC is undoubtedly much higher today, plus now similar machines would have 4 cores or more.

[yuhong]

I wonder why it took until later in 2006 before a version of Pentium M showed up with 64-bit support.

[nilsbunger]

Intel didn't release any 64-bit x86 processors until 2005. They bet so heavily on the alternative, Itanium, that it took them a few years to recover.

EDIT: it was actually mid-2004, as noted below.

[yuhong]

They release the first 64-bit Xeon in mid 2004.