Hmm I see the FSB and Multiplier both changed. Also the ram went from dual channel to single, maybe that be a clue ?

Horun wrote on 2025-11-29, 15:46:

Also the ram went from dual channel to single, maybe that be a clue ?

Oh! I had not spotted that, when I looked further all 4 DIMMs are reported as present by the SMBIOS and SIB reed all 4 sets of SPD, this is why 16GB is reported, but when I looked further only 8GB was available to Windows, so maybe one of the memory channels has failed, rime to try a different CPU.

The multiplier changing is expected, when the system is busy it's still x16.5

I swapped to an AMD Athlon II X2 245 (Regor) 2.90GHz [DA-C3] and all is back to how it should be, FSB is 202 and Windows sees all 16GB of Dual Channel RAM, same with a AMD Phenom II X4 955 Black Edition (Deneb) 3.23GHz [RB-C3]

Now back to the AMD Phenom II X6 1100T Black Edition (Thuban) 3.33GHz [PH-E0], Single Channel, only 8GB and 189 MHz FSB, I guess the CPU has half died.

red-ray wrote on 2025-11-29, 13:51:

On 2025-10-02 the FSB has 202 MHz, I just booted the system and now it's 189 MHz , what might have happened and how can I get it back to 202 MHz please.

I have already tried clearing the C-MOS to no avail.

Spread Spectrum is the issue... it has a direct influence on the FSB.
As in your screen shot, you have this set to auto, so it will change automatically. And the change can be as much as a 2% FSB drop in mhz.

Hard set Spread Spectrum to disabled. This will have no effect on anything else, and will force the 202mhz FSB.
Spread Spectrum was designed to reduce electromagnetic interference (EMI), it does so by modulating the clock signal (this is why you can get a changing variance between 189mhz and 202mhz), which can cause instability in some systems, especially those sensitive to clock variations.

Disabling it generally leads to better performance by allowing the CPU and FSB to operate at a more stable, constant frequency without the minor jitter introduced by the modulation.

Matchstick wrote on 2025-11-29, 20:45:

Spread Spectrum is the issue... it has a direct influence on the FSB.

Thank you, but I just changed it and with the AMD Phenom II X6 1100T Black Edition (Thuban) 3.33GHz [PH-E0] the FSB is still 189 MHz, the memory single channel and Windows only sees 8GB, not 16GB. The memory speed is only 1.23GHZ when it should be 1.51GHz = 8 x 189 MHz as the FSB:DRAM changed from 1:4 to 3:10.

All is as it should be when I install either my AMD Athlon II X2 245 (Regor) 2.90GHz [DA-C3] or AMD Phenom II X4 955 Black Edition (Deneb) 3.23GHz [RB-C3] whatever the setting of Spread Spectrum

I feel the Thuban must be half broken.