Utility ReBarUEFI allows you to modify the UEFI firmware on older systems and unlock the Intel Resizable BAR (Base Address Register) and AMD SAM (Smart Access Memory) functions – they give the processor access to the entire memory stack on the video card. Native support for these functions is available on Intel Core processors starting with the 10th generation and AMD processors starting with the Zen 3 architecture.
The function that allows you to increase performance is included in the PCI Express 2.0 bus specification, which means that, in theory, PCs with older processors can have access to it, as long as it is supported by the video card. The free ReBarUEFI utility with the UEFI DXE driver for systems not supported by official specifications will help you verify this statement. The corresponding module is embedded in the UEFI firmware and runs at every boot – it replaces one of the functions in the PCI resource allocation protocol (PreprocessController), checking the equipment for compatibility with Resizable BAR and SAM.
The developer of ReBarUEFI claims that he successfully tested the function on a system with an Intel Core i5-3470 processor (2012) and an AMD Sapphire Nitro+ RX 580 8 GB video card (2017) – it increased gaming performance by up to 12% with a BAR of 2 GB; and for the correct operation of Intel Arc video cards, the Resizable BAR function is generally necessary. According to Tom’s Hardware, the utility also supports Intel Sandy Bridge family processors from 2011. The developer page on GitHub presents list compatible motherboards, owners of which are asked to respond to confirm this information and clarify specific hardware configurations.
Most UEFI firmware will accept unsigned and patched modules even with the Secure Boot option active, so running games should not cause any problems. On some AMD Radeon video cards, the performance increase in games can reach 24%, but sometimes, on the contrary, a decrease in frame rate is possible. NVIDIA and AMD graphics card drivers have their own profiles for some games to improve performance with Resizable BAR and SAM.