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What is a 16550 and do I need one?
The 16550 is a UART with two 16 byte FIFOs. A UART is the part of a
serial port that takes byte-wide (characters) data and converts it to
bit-wide (serial) data, and visa versa. The FIFO is a buffer which
can hold characters until the CPU is ready to remove it or until the
serial line is ready to transmit it. The 'normal' UART in the PC (the
8250 or 16450) only has 1-byte FIFOs. The additional 15 bytes can be
useful when the CPU is busy doing other things - if the CPU isn't able
to remove data fast enough, it will be lost.
A very important thing to note is that under DOS, the CPU doesn't have
anything else to do, so the 16550 is wasted. Only under multitasking
operating systems does it really become useful. The 16550 will *not*
make your file transfers any faster, it will only prevent data from
being lost and relieve your CPU of some overhead. If you notice
system performance dropping like a rock when file transfers are
occurring, a 16550 may be helpful. If you see re-transmissions (bad
packets) or "FIFO overrun's" during file transfers under a
multitasking OS, try the same thing under DOS - if the errors go away,
then chances are a 16550 will be useful. If they remain, then your
problem is likely to be elsewhere.