[KLUG Hardware] Win (Software) Modems

[hardware@kalamazoolinux.org]

>I've been told not to buy a Win Modem.  Which, after a small amount
>of research, I've discovered appears to be a software modem.  So, I
>can understand why, if I use Linux.
Actually, Linux doesn't have that much to do with it, but good engineer-
ing does. Regardless of OS, a "Win modem" is a loser in my book; you're
using expensive CPU and memroy sycles to drive a process for which there
is good hardware and DMA around already. The idea here is to offload the
CPU, not merely from load, but from interrupt count. EVERY TIME a charac-
ter arrives, or is sent, the driver generates an interrupt, which means
that WHATEVER else is going on in the system will be stopped for a time
(at least one, usually serval CPU cycles), some you DON'T want with todays
pipelined instruction CPU systems. You might counter that you've got a 
lot of CPU speed to spare these days, but that's missing the point. It's
not mere CPU time that's used to drive the "Lose Modem" that you're was-
ting, but ADDITONAL interrupt and context switching time. While you will
soak off 5-10% of your CPU in driving/simulating the modem, you lose MORE
than that due to the other side effects.

>I've been told that I'm "out of luck" if I'm looking for a PCI Modem
>that's not a software modem.  
Simplistic, but as a percentage play PCI "real" modems are a rarity.
You do have to be *very careful* with this.

>I have to buy a more expensive external
>modem -- preferably a $100 US Robotics modem.
Nah, you can buy a cheap external modem if you want to; IMO you can
do considerably better than $100. Shop around a little!

>I'm not using Linux.  Why do I need a hardware modem?
Linux has little or nothing to do with this; there are Linux software 
modem drivers for some software modems right now. These things will
degrade the performance of your system in funny and unpredictable ways,
as hinted at by the explanation above. No good can come of this, re-
gardless of OS.

>Specific:
>I found a modem for $40 that is PCI modem.  It's the AOpen FM56-PM. 
>The vendor isn't sure if it's a software or a hardware modem.  Does
>anybody know?  The AOpen Website seems unhelpful.
When in doubt these days, assume it's a software modem. Write to them
and ask specific questions.

Stand up for yourself, and your CPU, man! :)

						Regards,
						---> RGB <---