Delivery Optimization: stopping Windows using your upload for other people's updates
SHORT ANSWER
Setting DODownloadMode to 0 under SOFTWARE\Policies\Microsoft\Windows\DeliveryOptimization restricts Windows Update to plain HTTP downloads and stops it sharing update files peer-to-peer with other machines. This is one of the few genuinely useful network tweaks, because the upload side can consume bandwidth and add jitter while you play.
Exactly what it changes
Read straight from the application source. If a tool will not show you this, it is asking for trust it has not earned.
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\DeliveryOptimization
DODownloadMode = 0
HTTP only — no peer-to-peer sharing, on the local network or the internet.
DoSvc — Delivery Optimization
Set to Disabled. Windows default is Manual (3), which is what a correct revert restores.
What it does
Delivery Optimization turns your PC into a peer that both downloads update content from, and uploads it to, other machines — by default including machines on the internet, not just your LAN.
Upload saturation is a real cause of ping spikes, because a saturated upstream delays the acknowledgements your game is waiting on.
When it helps
- Removes an unpredictable source of upstream bandwidth use, which is the kind that hurts latency most.
- Useful on connections with limited upload, which describes most consumer connections.
- Stops your machine serving update data to strangers.
When it hurts
- Updates may download more slowly, since they can no longer come from a nearby peer.
- On a LAN with many Windows machines you lose a genuinely efficient distribution mechanism.
How to undo it
Delete DODownloadMode and set DoSvc back to Manual — not Automatic, which was never the default.
Verdict
Worth doing on a normal home connection. If you run several Windows PCs on the same network and care about update bandwidth, leave it on.
Related guides
Everything else we change is listed too
All 127 optimizations are published in full, with what each one does and which are free. You can apply any of them by hand using pages like this one — the tool exists to do it in one click and put it back after every Windows update.