Re: Questions about buffered streams
On Jan 7, 11:50 am, Roedy Green <see_webs...@mindprod.com.invalid>
wrote:
On Mon, 7 Jan 2008 10:45:10 -0800 (PST), failure...@yahoo.co.uk wrote,
quoted or indirectly quoted someone who said :
So in theory, above code would write those 64000 bytes to a system in
aprox the same amount of time as Buffered stream would, assuming no
other thread blocks this output stream?
I'm assuming this since:
yes. however this is still some overhead for each call to write to
copy the bytes to the buffer. It has to check if the buffer is full
etc.
Actually, the disk is constantly spinning, so if you don't write in a
complete block, the disk may pass the position you want it to write to
before you write, so it would in effect be in the *worst* position for
the write.
Not to mention that typically disk IO happens in Sectors or Clusters,
which are usually at least 512 bytes long. Unless the OS itself does
some caching, writing one byte at a time is actually a read of 512
bytes, update of *that* buffer, and a write of 512 bytes. As you can
imagine, this is highly inefficient.
Something else to note is that you're discussion so far has assumed
Disk IO operations, but there are other forms of IO, including network
IO. Writing one byte at a time to a Socket stream can result in a lot
of overhead for the underlying protocols. I think that TCP/IP has a
minimum of something like 38 bytes, not to mention the ethernet and OS
overhead.