The HEART of a USB Bridge chip (your USB-to-to-Serial cable) is the Virtual Serial Port (VSP) DRIVER for you specific operating system.
That driver provides the interface for your OS to look at the USB device as a serial port (COMx).
The TRICKY PART is that a majority of amateur radio programs utilize the EIA-232/RS-232 control lines (RTS, DTR) for Push-To-Talk operation. The USB standard has NO hardware equivalent to those EIA-232 control lines.
---SO, that functionality is totally based on software, specifically the driver! ---
PROLIFIC, based in Taiwan, is the OEM mfg. of the PL2303 USB Bridge IC.http://www.prolific.com.tw/US/index.aspx
NEW Prolific Support webpage.Enter "guest" for both account and password to log-in.http://www.prolific.com.tw/US/CustomerLogin.aspx
Chinese counterfeiting of Prolific PL2303 USB chips has been widely reported.
You can read Prolific's official statements on their PL2303 Product and Driver Page.
Prolific now has a USA web site, and has introduced new USB chips and EOL for earlier counterfeited product lines.http://prolificusa.com/
PL-2303 Linux Driver for RedHat 7.3/8.0/9.0 Only
NOTE: No need to install drivers for following:
Linux Kernel 2.4.31 and above already includes built-in drivers for PL-2303 (VID_067B&PID_2303).
NOTE: Google Android OS is also based on Linux kernel so it also includes PL2303 drivers.