Resizable BAR: how to check whether it is on, and turn it on

What it does

Without Resizable BAR, the processor reaches the graphics card’s memory through a 256 MB window, moving it along as it goes. With it, the window covers all of the card’s memory at once. Games that send a lot of data to the card — large open worlds especially — run a few percent faster, occasionally much more.

A few games run very slightly slower with it, which is why NVIDIA’s driver uses it only for games NVIDIA has tested; AMD’s version, Smart Access Memory, applies to everything. Intel Arc graphics cards depend on it heavily, and Intel lists it as a requirement.

What it needs

• A graphics card that supports it: NVIDIA GeForce RTX 30-series and newer, AMD Radeon RX 6000-series and newer, and Intel Arc. Some early RTX 30-series cards need a firmware update from the card’s maker first.
• A processor and motherboard that support it: Intel Core 10th generation and newer, or AMD Ryzen 3000-series and newer (apart from the 3000-series G models with built-in graphics), on a board whose firmware offers the option — most from 2020 on, some only after a firmware update.
• Windows started in UEFI mode, not Legacy or CSM. Check this before changing anything (step 1 below).

Check whether it is on

• NVIDIA: open NVIDIA Control Panel, choose System Information at the bottom left, and find Resizable BAR on the Display tab: Yes or No.
• AMD: in AMD Software: Adrenalin Edition, Smart Access Memory is under Performance → Tuning. Its place varies a little between versions; searching the app for it finds it.
• Any card: the free tool GPU-Z shows Resizable BAR as Enabled or Disabled on its main tab.

Switch it on

1. Check that Windows started in UEFI mode. Press Win+R, type msinfo32 and press Enter. BIOS Mode must say UEFI. If it says Legacy, stop here: switching the firmware to UEFI only would stop Windows starting until its drive is converted, which Microsoft’s MBR2GPT tool does — a separate job, and one to do after a backup.
2. Update the motherboard’s firmware if its maker offers a newer version; older firmware may not have the option at all.
3. Restart into firmware setup, usually by pressing Delete or F2 as the PC starts.
4. Enable Above 4G Decoding. Resizable BAR cannot work without it. It is often in an Advanced, PCI Subsystem or Boot section.
5. Enable Re-Size BAR Support, sometimes called Resizable BAR, or Smart Access Memory on some AMD boards. On some boards it appears only once Above 4G Decoding is enabled.
6. Make sure CSM is disabled (Compatibility Support Module, or Legacy boot) — only if step 1 said UEFI.
7. Save and exit, then check again with one of the methods above.

If the screen stays blank after the change, make sure the monitor is connected to the graphics card rather than the motherboard. If it still stays blank, reset the firmware to its defaults as the motherboard’s manual describes; the card’s own firmware may need an update before it works with these settings.

Is it worth it?

Usually, yes: it is free and takes five minutes. Expect a few percent in most games and more in some, and measure your own games before and after to see what yours gain. On an Intel Arc card it is essential.

How Bottleneck checks this

On NVIDIA cards, Bottleneck reads the size of the window the processor has into the graphics card’s memory, through the card’s driver: 256 MB means Resizable BAR is off. It reports it switched off only where switching it on is possible — an RTX 30-series card or newer, on a desktop whose processor supports it — with the steps above.