Windows 10 Myth: Don’t Touch “Limit Reservable Bandwidth”


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Here’s an old PC myth that just won’t die: Did you know that your Windows PC only uses 80% of its available network bandwidth by default? You can speed up all your downloads by changing a setting in the Registry or Group Policy! Well, no. That’s not how it works.

How Windows 10’s QoS Packet Scheduler Works

This setting has existed since Windows XP, so this bad Windows tweaking tip has now been going around for 20 years.

Windows 10 has a feature called the “QoS Packet Scheduler.” It’s found in all versions of Windows, starting with Windows XP. QoS stands for “Quality of Service.” It’s a way of prioritizing certain types of network traffic, which is made up of packets.

QoS takes many forms. You might have a QoS feature on your wireless router or mesh Wi-Fi system. This would allow you to prioritize certain types of traffic: For example, you could ensure that all traffic to and from your work (or gaming) PC is high priority. This will help ensure that your work (or gaming) isn’t slowed downby another device that could be using a lot of your network bandwidth.

On Windows 10, the QoS packet scheduler lets the operating system reserve a certain percentage of your connection’s bandwidth for high-priority network tasks.

Which Programs Use This Reserved Bandwidth?

Applications running on your computer can use the reserved bandwidth for high-priority network tasks. They just have to tell Windows that certain traffic is high priority.

With the default setting, Windows guarantees that 20% of your connection’s bandwidth is always available to programs that ask for it. If your connection is being maxed out by a big video game or BitTorrent download, well, too bad for that download process—Windows will deprioritize the lower-priority network traffic and ensure that a high-priority task can get 20% of your connection’s bandwidth to work with.

Your download will take a bit longer, but there will always be a good chunk of bandwidth for a high-priority task—like streaming a video, perhaps.

How QoS Bandwidth Reservation Actually Works

The QoS Packet Scheduler’s “Limit reservable bandwidth” setting sets a maximum amount of a connection’s bandwidth that Windows will reserve for QoS. The key word here is “maximum.”

If no applications are telling the operating system that they need high-priority bandwidth at the moment, Windows will make 100% of it available to other applications. If an application is using 5% of your bandwidth for high-priority tasks, Windows will make 95% of it available to other applications.

At all times, Windows is making 100% of your connection’s bandwidth available. The myth says that unless you change this option, Windows will only use 80% of your connection’s bandwidth for other applications and leave 20% of it unused, just in case. That myth doesn’t make any sense, and that’s not how it works.

Why Would You Change This Setting?

According to this Windows tweaking myth that just won’t go away, you should change one of these settings to increase the amount of bandwidth available to your applications. However, changing the setting won’t really do anything—if you lower it to “0,” all you’re doing is ensuring that applications with high-priority traffic can’t use this feature to get ahead of lower-priority applications.

This could actually make the network applications that you care about less responsive. Don’t touch the setting unless you understand it and know what you’re doing.

Don’t believe us? Microsoft’s Raymond Chen wrote about this issue on his blog, The Old New Thing, back in 2006, calling it a “placebo setting” that was getting a lot of play at the time:

“The setting in question controls how much bandwidth can be claimed for high priority network access. If no program is using QoS, then all your bandwidth is available to non-QoS programs. What’s more, even if there is a QoS reservation active, if the program that reserved the bandwidth isn’t actually using it, then the bandwidth is available to non-QoS programs.”

He goes on to say, “So tweak this value all you want, but understand what you’re tweaking.”

If you like, you can change the percentage of bandwidth in the Group Policy Editor at Computer Configuration > Administrative Templates > Network > QoS Packet Scheduler > Limit Reservable Bandwidth.

It can also be changed in the Windows Registry with a DWORD value named “NonBestEffortLimit” underComputerHKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindowsPsched.

The "Limit reservable bandwidth" setting in Windows 10's Group Policy Editor.

But I Want Windows 10 to Use Less Bandwidth for Updates

Changing the “Limit Reservable Bandwidth” setting won’t make Windows 10 use less bandwidth for updates. Windows will still use just as much bandwidth for updates as it otherwise would, but those updates might now slow down your higher-priority network traffic.

There are other settings in Windows that give you power over this. For example, you can set a download bandwidth limit for Windows Update, or even tell Windows Update not to download updates automatically.

Why Won’t This Myth Go Away?

So why is this tip still so widespread on Windows tweaking websites, even in 2021?

We’ll let you in on a not-so-secret secret: There are a lot of low-quality websites out there. There are a lot of people writing Windows tweaking tips who don’t fully understand what they’re writing. It’s a big game of telephone. Once someone writes a tip and posts it online, it takes off, and other people copy it from website to website.

We don’t do that here at How-To Geek. We want you to know how technology really works. We bust Windows tweaking myths.We don’t spread them.





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