By HD anonymonk means Hard Disk. The seek times to move the heads around a hard drive are slow compared to memory access and geological compared to processor cache. What this means is processes that are dedicated to doing something to a file are normal disk IO bound. Lets not mention network latencies for now.

If you do manage to split this into threads you may actually reduce performance as each time a different thread gets a shot at it, it forces the HD to drag it's heads over to a completely different part of disk. A single thread reading the file sequentially will not be making the heads seek so much, assuming the file is not desperately fragmented on the media.

Then there are other users competing for those heads and tasking them off to the boondocks of the drive as far as your data is concerned which is why it was suggested you kick the lusers to try and get the disk all to yourself.

Cheers,
R.