There are basically two types of modems
available, traditional hardware based modems and software
based modems. Software modems have fewer chips on board,
the tasks that would have been done by the missings chips
are transferred to the host computer's main processor (the
Pentium, etc..).
Two functions performed by any modem
are:
Modem datapump functions - the
basic modulation/demodulation functions.
Modem control functions - hardware
error correction, hardware compression, AT
command interpretation.
US Robotics (now 3Com) manufactured
Winmodems still have the datapump chip, but modem control
functions are done by the host computer's main processor.
This slightly adds to the load on the main processor.
These modems are popular as OEM products, so when you buy
a new PC, chances are that your modem is winmodem.
HSP modems (Host Signal Processing), transfer
both datapump and modem control functions to the host
computer's main processor. This greatly adds to the load
on the main processor, which may be minimal on a 300MHz
Pentium II, but, really slows down a Pentium 133.
Pros:
Cost - software modems are cheaper
to manufacture.
Size - with less chips required,
software modems can be integrated on the computer
motherboard, ideal for laptop computers.
Easily upgraded.
Cons:
Requires a fast processor - the
faster the better.
Connection speed can depend on
processor speed - 28.8 or 33.6Kbps may be
marginal on a Pentium 100.
Disconnections can be a problem if
system resources are low. For example, using more
than 256 colour resolution can cause
disconnection due to competition with the
videocard for bus resources.
Danny Fye, who has experimented with various types of
modems writes:
"I just achieved a milestone for me. I got a
throughput of 6010 cps. A throughput of a connection
speed of greater than 52000 bps.
I have used these silly winmodems with mediocre results
of much less and always wished I could see something more
like what a 56k modem should fully be capable of.
I got me an external U.S. Robotics modem and put it on
the serial port and now real speed is finally a reality.
I am using Worldnet with Windows Me. I did myself a favor
and did a screen capture. The dun says I have a
connection speed of 50,666.
USB type modems can be operated in pretty much the same
way as a "winmodem." So one should not assume
that just because they have a USB modem that they will
get the full performance. I know better because I had one
and it worked very poorly. Even so, the brand of modem
can also make a big difference. I had an external Zoom
and it was good, but the external U.S. Robotics is
downright excellent!"
Dannys's experience with USB modems
echoes my own. Recently, a friend who had been having
connection problems with a software modem, ask me to
setup the replacement - a USB modem. Comparison of
connection speed and throughput between the two modems
showed that although the USB modem reported a higher
initial connection speed, its throughput was noticeably
lower.
In conclusion, software modems tend to
be unreliable. A hardware modem offers more performance
and reliability.
HSP modems (Host Signal Processing), transfer
both datapump and modem control functions to the host
computer's main processor. This greatly adds to the load
on the main processor, which may be minimal on a 300MHz
Pentium II, but, really slows down a Pentium 133.