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SubjectRe: Hyper-threading
Mike Dresser wrote:
> Indeed, I saw that. On the P4 2.66ghz that you have, the "second" cpu is
> disabled by intel, as they sell hyperthreading only on the newer Xeon P4
> (which you don't have), and the new 800FSB (4x200) units, which again
> you don't have.
> ..... CPU clock speed is 2672.7802 MHz.
> ..... host bus clock speed is 133.6388 MHz.

Some Pentium 4 chips support HT even when they officially "don't". For
example, my system has an Intel MB and a Pentium 4 2.8GHz processor; it
boots using HT just fine. From a recent boot:

Tycho kernel: CPU1: Intel Pentium 4 (Northwood) stepping 07
Tycho kernel: Total of 2 processors activated (11042.81 BogoMIPS).
Tycho kernel: cpu_sibling_map[0] = 1
Tycho kernel: cpu_sibling_map[1] = 0
Tycho kernel: Setting 2 in the phys_id_present_map
Tycho kernel: ...changing IO-APIC physical APIC ID to 2 ... ok.
Tycho kernel: ..TIMER: vector=0x31 pin1=2 pin2=0
Tycho kernel: testing the IO APIC.......................
Tycho kernel: .................................... done.
Tycho kernel: Using local APIC timer interrupts.
Tycho kernel: calibrating APIC timer ...
Tycho kernel: ..... CPU clock speed is 2783.0819 MHz.
Tycho kernel: ..... host bus clock speed is 132.0562 MHz.
Tycho kernel: checking TSC synchronization across 2 CPUs: passed.
Tycho kernel: Starting migration thread for cpu 0
Tycho kernel: Bringing up 1
Tycho kernel: CPU 1 IS NOW UP!
Tycho kernel: Starting migration thread for cpu 1
Tycho kernel: CPUS done 2

Note the "132.0562" MHz bus speed.

I obtained my system directly from Intel; however, I know of a few
people who obtained Pentium 4 chips from retailers, and their processors
support HT with a 4x133 bus.

Scott Robert Ladd
Coyote Gulch Productions (
Professional programming for science and engineering;
Interesting and unusual bits of very free code.

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