Resizable BAR: what it is and should you enable it

You may have seen "Resizable BAR" in a BIOS menu, a driver panel or a graphics card spec sheet and wondered if it is worth touching. It is a small setting with a modest effect, and on many PCs it is already on. This guide explains what it does, what your PC needs, how to check it and why the gain is sometimes zero.

What Resizable BAR does

A BAR (base address register) is the window a PCI Express device offers so the processor can reach its memory. For graphics cards, that window was traditionally small: PCWorld describes it as 256 MB at a time, even though modern cards carry far more video memory. To move a big chunk of data, the CPU had to work through many small pieces.

Resizable BAR lets the CPU see the whole video memory at once. NVIDIA describes it as an optional PCI Express feature where assets can be requested as needed and sent in full, and where several requests can run at the same time instead of waiting in a queue. AMD sells the same idea under the name Smart Access Memory (SAM). Intel and many motherboard makers use the name Resizable BAR or Smart Access Memory interchangeably.

What you need

All of these must support it, which is why the feature is easy to miss:

• Graphics card. NVIDIA introduced it on GeForce RTX 30 series cards, and some older cards in that family needed a VBIOS update from the card maker. AMD's version arrived with Radeon RX 6000 series. Intel recommends it for Arc A-series cards. For other cards, check your model's spec page.
• CPU and motherboard. Both must support it, and many boards need a BIOS update first. Check your motherboard maker's website for your exact model.
• Graphics driver. Use a current driver. If you are unsure how, see how to update graphics drivers safely.
• Laptops. NVIDIA tells laptop owners to ask the laptop maker whether a specific model supports it.

How to check if it is already on

On an NVIDIA card, open the NVIDIA Control Panel, go to System Information, and look at the details list. PCWorld says the Resizable BAR line should read "Yes". HWCooling describes the same System Information section as showing whether it is on or off.

If it says no, your hardware may not support it, or it may simply be turned off in the BIOS.

How to turn it on

Menu names differ by board, so use your motherboard manual for exact wording. The general steps:

1. Update the motherboard BIOS to the latest version from the maker's website, and install a current graphics driver.
2. Restart and enter the BIOS (the key is often Del or F2, but it depends on the board).
3. Enable Above 4G Decoding (some boards call it Above 4G Memory), then enable the Resizable BAR or Re-Size BAR Support option.
4. Turn off CSM (Compatibility Support Module) so the board boots in UEFI mode. Guru3D lists this, and notes the Windows drive must be UEFI-booted with a GPT partition style, not MBR.
5. Save, exit, and check again in the NVIDIA Control Panel or your graphics software.

Do not convert a drive from MBR to GPT or change boot modes without a backup. If Windows will not start after the change, set CSM back the way it was.

What gain to expect

Honest answer: usually small, and it depends on the game. NVIDIA says only that the feature "can increase performance in games" and gives no figures on its page. HWCooling reports NVIDIA's own range as a few percent up to 12% in certain games. PCWorld says AMD claims up to 16% and NVIDIA up to 12%, while its own test with a Radeon RX 6900 XT landed between 2% and 8%. Guru3D saw a few percent in some games, 5% or even 10% in others, and found that the vast majority of games hardly benefit at all.

Treat those as ceilings, not promises.

When it does not help

• Some games get slower. Guru3D measured negative scaling in at least one game, and PCWorld notes it can reduce performance in some cases. For this reason NVIDIA originally turned the feature on only for games it had tested, according to HWCooling.
• You are limited by something else. If your CPU or another part holds the graphics card back, a memory access setting will not fix it. Our guide on CPU or GPU bottleneck shows how to tell.
• Results vary over time. Drivers and BIOS updates change the picture, and Guru3D saw early gaps narrow after updates.

The exception is Intel Arc. Intel says Resizable BAR should be enabled for optimal performance with Arc A-series cards, although the cards can still work without it. If you own one, treat it as a requirement.

Checklist

1. Check that your card, CPU and motherboard support it.
2. Update the BIOS and the graphics driver.
3. Enable Above 4G Decoding and Resizable BAR (and turn CSM off if your board or guide asks for it).
4. Confirm it shows as on in your graphics software.
5. Test a game you play before and after, using the FPS to frame time calculator to compare results. If it is slower or unstable, turn the option off.

For bigger and more reliable wins, start with how to raise FPS in any PC game.