Resizable Bar or Smart Access memory as AMD likes to call it, has been widely available since AMD made it famous with the introduction of its Ryzen 5000 series processors and RX 6000 series GPUs back in 2020.
However, motherboard manufacturers neglected to implement the performance boost feature on older systems until 2020, leaving many gaming platforms without it. This issue was fixed by modder xCuri0 on GitHub, who published a mod with Resizable Bar that gives older systems access to it.
The mod modifies the UEFI firmware on older motherboards to add Resizable Bar compatibility. This is achieved by replacing the preprocessor function controller PciHostBridgeResourceAllocationProtocol in UEFI to a new feature that checks for compatibility with the panel’s Resizable Bar and then activates it if it is compatible. The size is set by adding a specific module to the DXE driver in the UEFI firmware.
The mod is reported to work on systems as old as the Sandy Bridge era, which came out in 2011. Technically, Resizable Bar has been around since the release of PCIe Gen 2.0. However, it never caught the attention of Intel, AMD or any of their motherboard partners until AMD realized its potential many years later and released it as Smart Access Memory in 2020.
The Resizable Bar changes the “aperture” of the PCIe bus, allowing for larger data transfers of more than 256 MB. In layman’s terms, you can think of the Resizable Bar as boxes on a conveyor belt. Without foundation, block sizes are limited to certain sizes, but with the feature enabled, block sizes can be significantly increased, increasing throughput.
Modern GPUs benefit greatly from variable bandwidth in the right scenarios. It’s not uncommon for some Radeon GPUs to increase performance by 5% to 24% in certain games with the Resizable Bar. But on the other hand, it can also reduce productivity. This is why AMD and Nvidia have variable lane profiles for each game and only enable them when necessary. Both GPU manufacturers can also set a specific Resizable Bar size to squeeze out as much performance as possible.
With this mod, older systems can gain extra performance that can only be achieved with the Resizable Bar. This is especially useful for users who want to upgrade their older machines with a brand new GPU that supports Resizable Bar. Some GPUs, such as Intel’s Arc A series, are so sensitive to the Resizable Bar that Intel requires it to be turned on for good performance.
