On Fri, 15 Dec 2000, Christof Lange wrote:
> I would like to extend Eric's question: Is it speed relevant
> whether I use internal or external modem on telephone line?
It depends. In the unlikely event you're using a Winmodem on a
machine with 8250 serial ports you'll only be able to get modem
connection speeds of 9600 baud, however, since there is "on the fly"
data compression, your data speed can actually be faster... I can
sometimes see download rates in Netscape given as 6.9KB/sec. The
compressed data which comes through the modem can only be
transmitted at 33.6kbps, but after decompression, the effective
rate is higher.
Note: kbps = kilobits per second, KBps = KiloBytes per sec
(I often see upper and lower case used interchangably.)
If you're using a hardware modem that's faster than 9600bps
there's a 16550 UART built-in, so you don't have to worry about
what kind of serial ports your motherboard has.
> Yesterday I downgraded my hardware (Arachne is progressing so
> fast that I am forced to change to slower PC!):
>
> from Pentium 333 MHz with internal modem 115 Kbps
> to Pentium 160 MHz with external modem 56 Kbps
The "115kbps" is the maximum data transfer rate of the 16550
UART. Setting this speed is relevant because of the data
decompression. Suppose you have your modem-to-bus speed set at
56kbps... and your actual modem to ISP connection is 42kbps. When
that compressed stream comes in at 42kbps and is decompressed in
the modem, you now have an effective transfer rate of say, 68kbps.
If your modem-to-bus rate is set at 56.7kbps, then there's a
back-up. The modem must pause while its buffers clear the
decomprssed data before any more data may be downloaded. This is
why it's always recommended to have your modem-to-bus rate set
higher than your modem connection speed.
> The result is impressive: Arachne seemed to work faster. To get an
> exact figure I ran WINDOWS and downloaded a file from a FTP
> site. The download display indicated a 1,5 times higher speed
> (instead of maximum 3,7 it was 5,5). What do these technical
> parameters XXX kbps actually mean?
Another discrepancy (though not that great) may arise from the
difference between a hardware modem and a winmodem.
You don't say which type your internal modem was. A winmodem
doesn't have an actual UART so it must use "spare" CPU cycles to
emulate one. If your machine is busy doing CPU-intensive tasks
(like rendering graphics on your browser) then the winmodem will
always be slower than a real modem, since it has to wait for the
CPU UART emulator, while the real modem never has to wait for its
dedicated hardware UART.
-
Steve Ackman [EMAIL PROTECTED]
Glass Host, Arts & Crafts http://www.delphi.com/crafts
Metamorphosis Glassworks Page http://twovoyagers.com/metamorphosis
