Re: apple IIGS

[CUTjefbla@bconnex.net (Jeff Blakeney)]

On Thu, 24 Dec 1998 21:14:23 -0700, Frank Carney
<frankcNOSPAM@cyberhighway.net> wrote:

>Where do you get the idea that a modem is anything other than a serial
>connection?  I does have buffers, and it can compress the data in the
>buffer before it is sent, but to the computer it looks identical to what
>was sent.  There is no way the file is going to get larger.  It may have
>transferred slower before and maybe the compression routines were slow,
>but the information goes in one side and is the same on the other side.
>Think about it, it is just a serial port to the program using the modem
>after you have connected.

Modem compression schemes before MNP 5 would increase the size of an
already compressed file.  This was because the algorithms being used
weren't smart enough to realize that the file was already compressed.

The reason this happens is in the way the files are compressed.  One
of the easiest methods is to put a count bytes in followed by data
(ie. $FF $20 would say that we are sending 255 space characters) and
sending two bytes is much faster than a large number of bytes (255 in
previous example).  Unfortunately, most compressed data doesn't have
this kind of repetition in it which is why adding count bytes will end
up making the file you send larger rather than smaller.

Since MNP 5 came out we haven't had to worry about this, though.  We
can turn on compression and it will send text data at up to 4 times
faster than sending it with no compression.  Already compressed files
will not get bigger and in some cases will still be reduced slightly
but generally take the same amount of time to transfer whether
compression is turned on or not.

By the way, because of the way TCP/IP works, turning on compression in
your modem while using TCP/IP, you will not see the 4 times
compression of text files.  TCP/IP splits data up into "packets" which
breaks up the repetition and such so data cannot be compressed very
much so there will be little improvement with having compression
turned on.  Just something to think about now that we have TCP/IP for
the Apple IIgs.

=== To ensure I see a reply please also e-mail me but remember to:
    CUT the obvious from my e-mail address to e-mail me
    Jeff Blakeney - Dean of the Apple II University on Delphi
*** HyperCard IIgs course now in session in the A2Pro forum on Delphi