What do the numbers of the (R)AM Benchmark tell me?

[Gooly]

Hi
I tested my pc with newly added RAM and after that I have this:



What doe these numbers tell me In terms of how and where I use them, or what I could do and what would be better not to do?
Thank you

[David (PassMark)]

The numbers on the Memtest86 RAM benchmark graph tell you the real life transfer speeds of your RAM / CPU combination.

PC5-51200 DDR5 RAM has a theoretical maximum data transfer speed of 51,200 MB/s (or 51.2 GB/s).

Here is the breakdown of how that number is calculated:

Module Name: PC5-51200
DDR Speed Rating: DDR5-6400
Transfer Rate: 6,400 MT/s (Mega Transfers per second)
Bus Width: 8 bytes (64 bits)

The Math:
6,400 MT/s×8 bytes=51,200 MB/s
3,600 MT/s×8 bytes=28,800 MB/s
(but double this for dual channel, so 57,600MB/sec)


The "51200" in the industry name (PC5-51200) is specifically chosen to represent this maximum bandwidth in megabytes per second. But this is just in theory. In practice several other factors effect the result, such as the CPU being used, it's cache, if you are in dual channel mode, if you are running XMP. You machine is getting pretty close to the theoretical number however (~40MB/s) for 3600MT RAM in dual channel mode.

For the specific graph in your screen shot is step size. The first test type, ‘Memory Speed Per Step Size’ accesses a large block, of memory in various sized steps. First, it runs through the block of memory sequentially, accessing every value. Next it runs through the same block again, except this time it accesses every second value. On this occasion, it runs through the block twice in order to access the same amount of data as the initial step. Next it runs through the same block again, except this time it accesses every fourth value and so makes four passes. And so on, until a certain maximum step size is reached. As you can see from the graph the performance for sequential access is around 20x better than taking large steps (this is unfortunate, but totally normal for PC hardware). This is not an intuitive result for most programmers who assume all memory accesses will be of equal speed. So good coding in a low level language can often get 10x performance gains, by keeping data close together.

In terms of what you can do to improve performance, there are a few basic "easy" things.
1) Run dual channel mode with matched RAM sticks in the "correct" slots as indicated by the motherboard manual.
2) Turn on XMP (if BIOS and CPU allow it). Also called DOCP on some AMD / ASUS motherboards.
3) Make sure the CPU supports the RAM speed. No point buying DDR5-6400 if your CPU only supports DDR5-4800.
4) Buy a CPU with a big cache

[Gooly]

In the Bios I firstly choose "Auto: Loads the optimal settings for the system" and MemTest (11.5) tested at DDR5 3600MT/s. No Error
Then I set in the Bios "DOCP I": Load the DIMM's default DOCP memory timings (CL, TRCD, TRP, TRAS) and other memory parameters optimized by ASUS.
But MemeTest tested again with DDR5 3600MT/s.
Only the (R)AM Benchmark seems to work with 6400 - the same number as in the Bios for the Mem. Freq. (see https://forums.passmark.com/memtest8...-ram-speed-how)
And additional question what does the curve tell me? What does the decline mean if step size > 8? Can I (shall I, do I have to) limit the step size to 8, but how, where, and what are the abbreviations in the bios for that?

[David (PassMark)]

There is the speed the RAM is capable of (programmed into it's SPD data), and the speed that it is running at (the value in use by the CPUs memory controller).
Both these values are display in BIOS and Memtest86 in various places. They often aren't the same.
In the screen shot above the PC5-51200 is the capability number, not the current speed.

And additional question what does the curve tell me?

Lots of things (see my previous post). But for me the most interesting thing is the decline in speed as accesses move from sequential to random.

Can I (shall I, do I have to) limit the step size to 8

It's software, the computer code, that determines what memory addresses to read and when and in what order. You can't control this unless it is your own software.

[Gooly]

Ahh - I understand, thank you very much and a successful 2026