While Ian Smith spoke about Modem Speed? to Peter Hocking

IS>
IS> PH> While Peter Collis spoke about Modem Speed? to William 
IS>Brackenridge
IS>
IS>PC>If by an 'ordinary serial port' you mean a 16450 or 8250 UART then
IS>PC>you
IS>PC>should be able to run a 28k8 or 33k6 modem without problems as 
IS>long
IS>PC>as
IS>PC>you don't run a multitasker (win/Desqview/OS2 etc)
IS>
IS> PH>  Get off the grass!
IS>
IS>Ahem.
IS>
IS> PH> With a 8250 or 16450 UART he'd be lucky to properly support a 
IS>V32 modem,
IS> PH> let alone V34 or V34+ modem!
IS>
IS>No, that's not so, Peter; not if you're not running multitasking.  A 
IS>10MHz XT with an 8250 UART (or an AT with a 16450) readily handles a 
IS>57600bps port at sustained rates, though 115200bps tends to be a bit 
too 
IS>flakey.
IS>
IS>When I first got my 386sx16 in 1991, I tried out a shareware 2-node 
IS>serial network called Weaklink, successfully transferring the entire 
IS>20Mb from my existing XT HD to the sx16 at 57600bps from an 8250 UART 
IS>(averaging about 5kCPS, I recall), with next to no retries at the 
IS>network driver level.
IS>
IS>Multitasking (ie interrupt latency) changes the picture completely, 
IS>including some disk caching software on an otherwise non-multitasked 
PC. 
IS> No way can you run an 8250/16450 UART successfully under Windows or 
IS>OS/2 or Desqview, even on a Pentium, but what Peter Collis said is 
quite 
IS>correct.
IS>
IS>Ian
IS>

Ian,

I beg to differ. Certainly I have found that Laplink using ordinary serial 
ports successfully sustains transfer speeds such as you suggest, but my 
experience and that of friends using mainly Telix, (dos version), found 
that a V32bis modem that established a V32bis connection could not 
reliably sustain that connection speed with out 16550 uarts.

Any connection at that speed tended to suffer from port over runs, dropped 
characters, lots of retrys and fluctuating download speeds, all fixed when 
we added 16550 uarts.

I should point out that we were all running our dos communications 
programs from the dos prompt, with out a multitasker/task switcher being 
loaded.

?

Have a great day,

Peter *:-)

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