Saving Quotes on another folder than the "experts/files"



I want to program an EA which is writing and reading from a csv-File from drive D:\\

I am using the kernel32.dll and can write on D:\\, but not read at the same time.

Everything works with the metatrader-file functions and the "experts/files"-folder?

Is there a difference to use the kernel32-functions than the metatrader-file functions?

With how many different accounts can I write and read to one csv-File? How fast can I do this?

Does anybody has some experience to the limits??