Disadvantages
Winmodems have earned a certain notoriety for slowing down their host computer systems and for having buggy drivers, although this reputation was largely garnered during the period of their introduction to the mass market, whereupon they were apt to use substandard drivers and be found in entry-level computers with slow CPUs. Any such reputation has not, however, halted their market popularity; most internal 56k modems produced since 1998 have been software-based.
Nowadays, with modern CPUs and better drivers, their most serious drawback is that they are operating system and machine dependent. They cannot always be used on other operating systems and host machines because the driver support requires far more effort to produce.
They consume some CPU cycles on the computer to which they are attached, which can slow down application software on older computers. They are sometimes referred to as a "port-on-a-stick".
The advantage of software upgradeability was diminished when many newer hardware modems gained the ability to upgrade firmware to support new standards. Modems such as those made by U.S. Robotics used generic DSP architecture, which achieves the flexibility of softmodems, without sacrificing compatibility.
Read more about this topic: Softmodem