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about_fids_vids_and_dids [PHCwiki]
 
Table of Contents

Intel publishes some nice datasheets with extended information, including voltages for their products, on their webpage.

FID

FID means Frequency ID and is the integer expression of a register that indicates the divisor to the base frequency (the BUS frequency).

An information found on the Intel(R) Software Network Support declares that FID 6 is the lowest FID available on Core(2) CPUs.

The FID is stored in the first 6 Bits within the Byte read from the MSR. To retrieve a FID correctly you need to use the bitmask 00111111 (decimal: 63).

VID

VID means Voltage ID and is the integer expression of a register that indicates the internal signal to the voltage regulators.

The VID that is applied for the lowest available frequency on a Core(2) CPU is also the lwoest possible for every higher frequency. This value seems to be hardware-fixed.

DID

DID means Division ID and is the integer expression of a Bit that indicates if the BUS-Frequency is internally halved. Intel is naming that feature “Dynamic FSB Frequency Switching or Super Low Frequency Mode (SLFM)”.

Halving the BUS frequency is note by stepping each second clock tick on the BUS. The BUS-frequency itself does not change but the CPU internally not got only 50% of the BUS speed.

Example: A given CPU uses three different working frequencies which are generated with different BUS-frequencies:

Clock Rate interlal BUS frequency multiplicator
800MHz 400MHz 2.0
1200MHz 400MHz 3.0
2200MHz 800MHz 3.0

The DID is stored in the 16.th Bit within the Data read from the MSR. To check if a DID is set to HIGH or LOW you need to use the bitmask 10000000 (decimal: 128).

HID

HID stands for Halving ID and indicates a Bit on the Data read from the Register that enables or disables an additional 0.5 to the given FID.

If there is a FID “9” set and HID is enabled the FID is internally “9.5”.

Note: Intel CPUs (Core, Core2, possible i-Series) does not allow FIDs lower than 6.

 
 
about_fids_vids_and_dids.txt · Last modified: 2012/05/30 01:35 by thejj
 
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