On Fri, 15 Dec 2000 13:51:07 +0700, Eric Yaeger wrote:
> You said that you are running a 56K modem on a 486DX4 computer.
> I have a question for you. I want to know, in your experience or
> knowledge, whether or not your computer is capable of actually
> operating at 56K? [Is it a 100MHz 486DX4]
>
My experience suggest that it's mainly down to the serial port
interface card that you use, assuming that the software is sound (i.e.,
isn't windoze....)
Originally, my serial ports used 8250 UART chips and these will not
cope with a connection TO THE MODEM (NB: NOT line rate) of 115200 baud.
I removed one of the 8250 chips and put a 16550 chip in its place. This
chip has an internal buffer to collect received bytes until the CPU
can come and collect them. This enabled me to increase the port speed to
57600 baud. I suspect that the fact that my serial card is still only
an ISA 8-bit card (even with the faster UART in it) is why it still
won't go reliably with Arachne at 115200 baud.
Using 57600 baud between PC and modem, I seem to get LINE speeds of
around 44000 using a DX4-100 CPU. That may be due to the poor quality
of the BT telephone line or it may be limited by the bottleneck between
PC and modem. Obviously, if your connection between PC and modem is only
running at 38400 baud, you can't have the line rate going at 56000
without there being a pile-up of delayed characters somewhere! And
finally, of course, even if the whole system were to enable line speeds
of 56000, it would practically NEVER run at that due to other
bottlenecks elsewhere on the internet - how many times have you waited
for minutes for a 2000-byte file to download? That all makes the modem
numbers game a little futile, doesn't it?
Newer 486 motherboards (than the one that I have) do have their
serial ports built-in and these may well run reliably with Arachne on a
DX4 at 115200 baud. I have one to try but as yet haven't got around to
it - usual story!
Hope this helps.
Ron.
