I am running Windows 10 Pro, set up 2 separate Ram Disks on the same machine, each getting over 30GB of space. I then copy a single file that is around 12GB in size onto one Ram Disk. Then I clear the Windows file cache. Subsequently I drag the file from the first ram disk onto the window of the second ram disk.

What I am seeing is an average 1.5-2 Gigabytes/second transfer speed.

Question: What is bottle-necking the transfer speed here? Same machine, one CPU that runs at around 4GHz with multiple cores, two identical memory disks with their own memory regions on the same machine accessing fast DDR4 2666 memory. I do not understand what constrains the transfer speed here, I understand that the standard Windows file transfer consists of a single threaded process.

I know there are file copy tools that can spin off multiple threads and I know for some 2GB/sec is very fast. But my question focuses on what is slowing down single threaded file copies on the same machine from memory to memory when not a single core is fully utilized during the file transfer, DDR4 memory has an over 10 fold throughput. I understand the Windows APIs consume overhead but nothing indicates that a single hardware resource is constraining the throughput speed here. This is a pure Windows issue and I like to learn whether there are settings/options in the OS that constrain the throughput.

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