> >>>>> "G" == George Toft <[EMAIL PROTECTED]> writes:
>
> G> I would invite you to do the math: 115,200 baud with one start bit,
> G> one stop bit and eight data bits (total of 10) means the computer
> G> has to pump out 11,520 bytes per second to the serial port. I
> G> think if a 386 at 25Mhz can handle a hard drive and move 700K bytes
> G> per second, it can surely handle less that 12K, especially since
> G> the modem has a higher priority interrupt than the hard drive.
>
> If a modem were a hard drive, that would be correct. But it's not.
>
> First, the hardware controlling a hard drive is quite different than
> serial hardware. Serial hardware has very samll buffers. If the CPU
> doesn't service it in a very short amount of time, characters are
> lost. A hard drive often has DMA, and certainly has different
> hardware buffering it.
In the dark ages from whence I came, the serial card could buffer 16
bytes
and a hard drive 256 bytes. Even with these numbers in a single-tasking
DOS, I saw the above performance on 286's.
> Second, the CPU is doing vastly different things when it runs a PPP
> connection vs. reading from a disk. There's a lot to be done in a TCP
> stack, which is why with even fast computers, sniffing on an ethernet,
> for instance, can drop packets. There's less work to be done on a PPP
> link, but there's also a much smaller CPU.
>
> --
> Alan Shutko <[EMAIL PROTECTED]> - By consent of the corrupted
> You will be run over by a beer truck.
Aahhh - Being new to Linux I'm sure I misspoke. When I was deep in
the DOS world, we had no problems with high-speed modems and NICs on 286
and 8088's. I see that Linux has far more to do than just listen to
a serial port. Please forgive my mouth overrunning my brain and not
thinking Linux.
My gut feeling, considering the extreme talent that went into making
Linux, is even a lowly 386 should be able to keep up with a 28.8 modem.
George
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