Syscalls are not the only consumer of wall clock time, which is what was measured.

> To read in binary, you open with 'rb' and not just 'r'.

No. "The default translation mode is 'b'." [1] And even in 't' mode, it's still reading bytes in PHP vs UCS-2 characters in C#.

[1] https://www.php.net/manual/en/function.fopen.php

but it makes function calls, it's not neglectable as it's called as many time as the bytes the file has

That’s the api provided, and part of the point. The other option is to read the buffer directly, but it isn’t exposed to the programmer.

the overload is right below it

  int StreamReader.Read()
  int StreamReader.Read(char[] buffer, int index, int count)

https://github.com/dotnet/runtime/blob/1ba0394d71a4ea6bee7f6...

You just need to do File.OpenRead instead of OpenText to get a FileStream, then you can read the buffer