What is Resizable BAR?
It is a feature of the PCI Express slot that lets the processor see the whole memory of the graphics card at once. Without it, the processor reaches that memory through a small window of 256 MB and has to move data through it piece by piece. With it, the window is as large as the card's memory. AMD calls the same feature Smart Access Memory. It is a setting, not a part: it costs nothing, and it only has to be switched on in the BIOS.
Does it make a difference?
It depends on the graphics card and on the game. On Intel Arc cards it matters a lot: Intel says these cards need it to perform as intended, and without it they are clearly slower. On NVIDIA and AMD cards the gain is smaller and changes from game to game. NVIDIA drivers switch it on only for games where it helps. In every case there is no reason to leave it off on a PC that supports it.
Which PCs support it?
The graphics card, the motherboard and the processor all have to support it. Most gaming PCs built from parts of roughly the last five years do, sometimes only after a BIOS update. If the setting is missing in the BIOS, look for a newer BIOS version on the motherboard maker's support page.
- NVIDIA: GeForce RTX 30 series and newer. Some early cards of that series need a firmware update from the card maker.
- AMD: Radeon RX 6000 series and newer.
- Intel: all Arc graphics cards.
- Windows must be installed in UEFI mode, not in the old legacy mode.
How do you check whether it is on?
The graphics driver tells you. On an NVIDIA card open NVIDIA Control Panel and click System Information: the list has a line named Resizable BAR that says Yes or No. On an AMD card, AMD Software shows it as Smart Access Memory, enabled or not. On an Intel Arc card, Intel's graphics software shows it and warns you when it is off. The free Configurator app for Windows reads the same state for any of the three and shows it next to the boot mode, so you can see at a glance what is missing.
How do you enable it?
You enable it in the BIOS. First check the boot mode in Windows: press the Windows key, type System Information and open it. The line BIOS Mode must say UEFI. Then restart, press Delete or F2 to open the BIOS and change the settings below. The names differ by motherboard maker, and the Resizable BAR setting often appears only after the first two are set.
- Switch CSM (Compatibility Support Module) off, so the PC starts in UEFI mode.
- Switch "Above 4G Decoding" on.
- Switch "Resizable BAR" or "Re-Size BAR Support" on, or set it to Auto.
- Save, restart and check in the graphics driver again.
What can go wrong?
The one real risk is the boot mode. If BIOS Mode in System Information says Legacy, Windows was installed the old way, and switching CSM off will stop it from starting. Nothing is lost in that case: go back into the BIOS, switch CSM on again and Windows starts as before. To use Resizable BAR on such a PC the system disk has to be converted to the UEFI layout first, which is a bigger job and needs a backup. If the setting is on in the BIOS but the driver still says No, update the BIOS and the graphics driver.