” A modem for a PC may be either internal or external. The
internal one is installed inside of your PC (you must remove
screws, etc. to install it) and the external one just plugs into a
serial port connector on a PC. Internal modems are less expensive,
are less likely to to suffer data loss due to buffer overrun,
usually use less electricity, and use up no space on your
desk.”
“External modems are usually easier to install and usually
require less configuration. They have lights which may give you a
clue as to what is happening and aid in troubleshooting. The fact
that the serial port and modem can be physically separated also
aids in troubleshooting. External modems are easy to move to
another computer.”
“Unfortunately most external modems have no switch to turn off
the power supply when not in use and thus are likely to consume a
little electricity even when turned off (unless you unplug the
power supply from the wall). Each watt they draw costs you about
$1/yr. Another possible disadvantage of an external is that you
will be forced to use an existing serial port which may not support
a speed of over 115,200 bps (although as of late 1998 and late 2000
most new internal modems don’t either –but some do). If a new
internal modem had say a 16650 UART it would put less load on the
CPU.”