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From: dillon@CORY.BERKELEY.EDU (Matt Dillon)
Newsgroups: net.micro.amiga
Subject: Re: File random access times.
Message-ID: <8608281956.AA19132@cory.Berkeley.EDU>
Date: Thu, 28-Aug-86 15:56:50 EDT
Article-I.D.: cory.8608281956.AA19132
Posted: Thu Aug 28 15:56:50 1986
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>Using the Manx compiler, version 3.20a, I did some timings on random
>file accesses. Here are some of the interesting results:

	Interesting results.   I would like to comment on your comment on
buffered I/O speeds (and buffered I/O in general, this isn't a flame or
anything).

>it seems like if call
>read() with character count of 1000 or so, unbuffered I/O is faster
>(I guess in this case it becomes equivalent to doing your own buffering.)

	My comment is that buffered I/O is useful when you are reading a lot
of junk in small segments.  For instance, try reading 8K one character at a 
time.  With unbuffered I/O, things go slowly.  With buffered I/O, reading is
an order of magnitude faster.  Additionaly, if you are making small relative
seeks, buffered I/O wins because most of the time the data is already in
the buffer and it doesn't have to make a system call.

	There is another use for buffered I/O:  Think of the situation 
where you are reading files and writing files on the same disk.  If you use
unbuffered I/O, the poor disk is continuously seeking between the track it's
reading and the track it's writing (because the sector cache is NOT a track
cache).  However, if you use buffered I/O with, say, a 4K input buffer and
a 32K output buffer, disk seeks are lessed and overall program speed 
increases by an order of magnitude.

	Finally, due to the bug in the RAM: disk, you always want to use
buffered output when writing to RAM: files.  If you write in smaller segments
to the RAM: disk, an incredible amount of memory is wasted for some reason.

					-Matt