Update: I got 4k 120hz working on my monitor. Not sure how to share the driver or what rules there are about this sort of thing.
Driver 71 change log — Quadro P2200, Windows XP SP3 32-bit, ASUS XG27UQDMS, direct DisplayPort
**What changed from Driver 70**
Driver 71 adds one monitor-specific timing rule to `[nv_timingRestrictions_addreg]` in `Display.Driver\nv4_dispi.inf`. The NVIDIA miniport and display DLL are identical to Driver 70. Driver 69 is the rollback build.
```ini
HKR,,NV_R&T,%REG_SZ_APPEND%,"R&T0000=3840,2160,32,120,*,AUSAA34,ADD,OEM,106656,4000,48,32,2222,3,5,+-"
```
**Why the entry was needed**
The ASUS advertises 3840 × 2160 at 120 Hz using CTA video code 118. The part of the XP driver that builds the mode list accepts codes 1 through 34, so it skips 118. The working 4K60 mode comes from a separate detailed timing in the monitor’s EDID. That explains why XP listed 4K60 but omitted 4K120.
**How the timing fits**
The new entry keeps the porches, sync widths and totals from the monitor’s working 4K60 detailed timing. At 120 Hz, those totals give `4000 × 2222 × 120 = 1066.56 MHz`. The standard CTA 4K120 timing calls for 1188 MHz. The custom timing fits the driver’s tested 1074.63 MHz limit for RGB at 8 bits per channel over HBR3 ×4.
| Timing | Active | Front porch | Sync width | Back porch | Total | Polarity |
|---|---:|---:|---:|---:|---:|---|
| Horizontal | 3840 | 48 | 32 | 80 | 4000 | + |
| Vertical | 2160 | 3 | 5 | 54 | 2222 | − |
**Why selecting the saved mode matters**
In an offline replay of the XP driver, submitting 1066.56 MHz through the custom-mode validator triggered an EDID range rejection and a fallback to 60 Hz. Selecting the installed 120 Hz entry took a different path: the driver found the ASUS timing in its saved list and passed 1066.56 MHz to the DisplayPort output code. The bandwidth check remained active and selected 8 bits per channel on the link. XP’s desktop setting was 32 bits per pixel.
This is the timing change from an already working P2200 Driver 70 build. The single INF line does not supply the earlier P2200 support needed with a stock NVIDIA XP driver.
