Intel Core 2 Quad Q9400S
Drops into a supported LGA 775 board as it is; check the board's CPU list. How to check.
Intel Core 2 Quad Q9400S: 4-core, 2.66 GHz, Yorkfield, LGA 775, 1333 MT/s FSB, 6 MB (2 x 3 MB) L2, 65 W TDP.
Same clock, same cache, less power: the Q9400S keeps the Q9400's 2.66 GHz, 6 MB of L2 as 2 x 3 MB and 1333 MT/s bus, with the TDP cut to 65 W. It came later, in Q1 2009, as SLG9U on the R0 stepping, CPUID 1067A. Intel lets the S parts run to a 76.3 °C Tcase, higher than the regular Q9400's limit, so the lower TDP does not come with a tighter thermal ceiling. That suits a quiet office tower or a small form factor case where a big tower cooler will not fit. VT-x, SSE4.1 and Enhanced SpeedStep all stay, and the VID still spans 0.85 V to 1.3625 V.
| Family | Core 2 Quad |
|---|---|
| Codename | Yorkfield |
| Socket | LGA 775 |
| Cores / threads | 4 / 4 |
| Base clock | 2.66 GHz |
| Front-side bus | 1333 MT/s (333 MHz base clock) |
| Multiplier | 8x |
| L2 cache | 6 MB (2 x 3 MB) |
| TDP | 65 W |
| Process | 45 nm |
| Launch | Q1 2009 |
| Dual-socket capable | No |
| VT-x | Yes |
| SSE4.1 | Yes |
| Enhanced SpeedStep | Yes |
| Max case temperature | 76.3 °C |
| Voltage range (VID) | 0.85 V to 1.3625 V |
Steppings and microcode IDs
| Stepping | CPUID | sSpec |
|---|---|---|
| R0 | 1067A | SLG9U |
A BIOS needs a microcode update matching the CPUID (and, for Xeons, the LGA 771 platform ID). See LGA 771 Xeon microcode and how to read your stepping.
Mod notes
Native LGA 775, so the work is paperwork: find the Q9400S line on the board's support list and the BIOS version beside it. Before flashing that version, save the old BIOS to a file, since a failed write is far easier to recover from with a copy in hand.