Data Transfer Speed

[Farabi]

Is transfering data from a buffer to buffer depend on harddisk speed too?

[Mark Jones]

Well, this may depend... what do you mean by a "buffer?"

[donkey]

Hi Farabi,

If you think about the question you will realize there is no answer possible. Since Windows can use the hard disk as virtual memory, there is never a solid guarantee that a memory buffer is not actually partially or wholly residing on the disk. Conversely since modern hard drives can have very large memory caches it is completely possible that a file on your hard drive is held in its cache and is not drive speed dependent. So in any scenario the answer is both Yes and No at the same time.

[MichaelW]

I think more often than not, the answer would be no. I think anything in the drive's cache would typically also be in the (much larger and much faster) system disk cache. And if it were not, it would still need to be transferred over the drive's interface, and while the interface transfer rate is typically much higher than the drive's internal transfer rate, it's far below system-memory transfer rates.

[Farabi]

Im sorry, I cannot express my mind.

I heard that windows used virtual memory, which mean if OS memory above the Physical memory it uses harddisk to store it as temporary files.

[Tedd]

It does, but only when those portions are not currently in use - when they are required, they will be put into memory again. So, a copy from one memory buffer to another will still be a memory -> memory copy. (Though there could be a short delay while they are pulled into memory the first time - if they haven't been used for a while.)

[Farabi]

It does, but only when those portions are not currently in use - when they are required, they will be put into memory again. So, a copy from one memory buffer to another will still be a memory -> memory copy. (Though there could be a short delay while they are pulled into memory the first time - if they haven't been used for a while.)

So that delay is happen on the memory not because it were being put from harddisk to memory?

[Tedd]

IF the section of memory was in the page-file, it would need to be put back into memory first -- that will cause a delay. But only on the first access (i.e. the first byte,) after that, all bytes will have been put into memory (unless it's a very large section.)
In general, don't worry about it - if your program is running, it will be in memory (unless the system is very low on spare memory.)

[BlackVortex]

In general, don't worry about it

+1
Trust the windows memory management !

[dedndave]

I am fairly certain that the drives' internal cache is governed by a very different
set of rules, as compared to the OS cache(s). It is primarily used to reconcile
the differences between the bus transfer rate and the physical drive transfer
rate. It is likely emptied as soon as the drive mechanics are able to handle any
pending transfer(s) that may be in the queue.