Windows 11 memory allocation

Harve · Oct 16, 2023

Modern Intel procesor provide multiple memory banks for overlapping core accesses to memory. Sapphire Rapids W-2400 processors have 4 memory channels and W-2500 series has 8 memory channels. How efficient is Windows 11 at allocating memory across banks/channels in order to maximize performance?

iko22 · Oct 19, 2023

As far as I am aware, allocating memory across banks/channels is accomplished within the DDR SDRAM architecture (Intel or AMD). It is therefore transparent to the Windows Operating System.

A third bank group bit (BG2) was added, allowing up to eight bank groups.

Source:

DDR5 SDRAM - Wikipedia

en.wikipedia.org

DDR5 doubles the number of bank groups while leaving the number of banks per bank group the same. Increasing banks groups is key as bank accesses to different bank groups require less time delay between accesses, compared to bank accesses within the same bank group. Banks within the same bank groups share local I/O routing, sense amplifiers, and array blocks, which introduce longer timing constraints. Doubling the total overall banks is also key as this improves overall system efficiency by allowing more pages to be open at any given time, thereby increasing the statistical probability of high page-hit ratios.

Source:

DDR5: The Next Step in System Level Performance: Part II

In this follow-up blog, I discuss, in a little more detail, some of the features on DDR5 that allow performance gains and scaling capability.

www.micron.com

Multiple Banks (Interleaving) and Channels
• Multiple banks

• Enable concurrent DRAM accesses
• Bits in address determine which bank an address resides in
• Multiple independent channels serve the same purpose

• But they are even better because they have separate data buses
• Increased bus bandwidth

Source:

https://pages.cs.wisc.edu/~sinclair/courses/cs752/fall2020/handouts/lecture/12-dram.pdf

Multiple Open Banks
– Open Banks make for faster access IF your going to that bank on the
next access…performance hit if your not
– Power hit when banks are open

Source

http://www.ddrdetective.com/files/1614/2377/7794/7-WE5Slides_CriticalMemoryPerformanceMetricsFor.pdf