Software Modems

Software modems

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.

Picture of a modem chip - 7K 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.

In conclusion, software modems tend to be unreliable. A hardware modem offers more performance and reliability.