They are "Serial" data ports. The data is delivered on a single line as a
stream of bits. A standard PC has a total of 4 Com ports. Com-1
and Com-3 share an IRQ(4), but have a different Address. Com-2 and
Com-4 share and IRQ (3), but have different addresses.
They are setup via BIOS. You will find them in Device Manager under
the Ports category.
Modems use a dedicated Com port on the card itself, usually taking up
Com 1 or Com 3. In days gone by, configuring Com ports was a real
headache with addressing and IRQ conflicts.
They have been essentially replaced by Universal Serial Bus devices,
where up to 128 individual devices can be chained on a single USB channel.
Nothing outdated about using external modems, plotters, UPS monitoring,
etc. If COM ports weren't in demand or needed OEMs would stop making PCs
with them, just like they did with the 5.25" floppy drive.
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