Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!utastro!bigtex!james
From: james@bigtex.cactus.org (James Van Artsdalen)
Newsgroups: comp.sys.ibm.pc
Subject: Re: File creation error
Keywords: 224 File(s) copied; slow; Compaq; MS-DOS 3.3
Message-ID: <14520@bigtex.cactus.org>
Date: 3 Mar 89 14:14:12 GMT
References: <7852@ihlpf.ATT.COM>
Reply-To: james@bigtex.cactus.org (James Van Artsdalen)
Distribution: usa
Organization: Institute of Applied Cosmology, Austin TX
Lines: 31

In <7852@ihlpf.ATT.COM>, pcl@ihlpf.UUCP (pcl) wrote:
> I encountered the following error when trying to copy 300 files (small size)
> from harddisk to A: (1.2 meg floppy drive):

> [...]

> Also, why the copying process is VERY slow (over 5 minutes)?

Several people pointed out that the root directory on a hard or floppy
disk is of a fixed and limited size, whereas a subdirectory could have
grown.  But no one pointed out a potential cause of slowness: lack of
buffers.

Mess-DOS uses the config.sys BUFFERS= mainly for directory sectors so
it doesn't have to re-read them constantly.  pcl's 224 files
constitutes 14 sectors worth of directory.  Towards the end, every
file added meant that all preceding N sectors of directory had to be
read linearly.  Once N exceeds the number of buffers, each and every
directory sector must be physically read.  In this case we would want
the config.sys BUFFERS= entry to be at least 2*N, so that we could
hold the source and destination directories entirely within RAM.

Another part of the problem is this: If 300 files were indeed intended
to fit in a 1.2meg disk, then the average file size was 4K or less.
But for files residing on the 8th directory block or later, DOS had to
read more than 4K of directory entries.  Hence the mere size of the
directory made the disk access very much slower, because the amount of
directory reading could exceed the amount of file reading.
-- 
James R. Van Artsdalen          james@bigtex.cactus.org   "Live Free or Die"
DCC Corporation     9505 Arboretum Blvd Austin TX 78759         512-338-8789