Memory speed tiers/DDR5/DDR5-6400
DDR5-6400 bandwidth
DDR5-6400 transfers data 6,400 million times a second on every bit of the bus. On a 128-bit bus that is a theoretical peak of 102.4 GB/s.
Theoretical peak, by bus width
| Bus width | Theoretical peak | Arithmetic |
|---|---|---|
| 64-bit | 51.2 GB/s | 6,400 MT/s x 64 bits / 8 / 1000 = 51.2 GB/s |
| 128-bit | 102.4 GB/s | 6,400 MT/s x 128 bits / 8 / 1000 = 102.4 GB/s |
| 256-bit | 204.8 GB/s | 6,400 MT/s x 256 bits / 8 / 1000 = 204.8 GB/s |
A DDR5 module also carries 64 data bits, split into two independent 32-bit subchannels. Two modules in dual channel make a 128-bit bus.
The peak is arithmetic, not a measurement: the data rate times the bus width, divided by 8 bits per byte and by 1,000. Memory never delivers all of it. Refresh cycles, switching between rows and the traffic of every other core take a share, so a measured figure below the peak is expected and is not a fault.
The RAM speed test measures the bandwidth your machine delivers from the browser, from one thread and from all of them. Read that figure against the row above that matches your bus: one module or channel is 64-bit, two in dual channel are 128-bit.
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