Buffer Size; Chapter 4 Page 45 - Brainboxes CC-265 Hardware Manual

PCI Quad RS232
that:-
port#1 is mapped as COM2
port#2 is mapped as COM3
port#3 is mapped as COM4
port#4 is mapped as COM5
For example:
/L 300,7,3,4,5,6
sets up a card with a status register at 0300H. The card uses
interrupt 7 as the shared interrupt line. Ports 1 and 2 are designated
as COM3 and COM4, Ports 3 and 4 are designated COM5 and
COM6, and all the shared interrupt IRQ 7.
Multiple cards can be installed separately, each card using its own
status registers and interrupts. Note that although linked cards can
share interrupts, separate cards cannot share any interrupt line.
/L 0120,7,3,4,5,6 1st card SISR at 0120
/L 0300,10,7,8,9,10 2nd card SISR at 0300
The interrupt line specified in the /L switch overrides any
interrupts set via the /I switch for the same COM ports, because
cards use a slightly different mechanism for interrupts.

Buffer Size.

Switch: /S n
Purpose:
Set size of all buffers in bytes. n is rounded to the nearest power of
2, and must be in the range 32 to 32768. For any serial port opened
two buffers of size n are allocated, one for input and the other for
output. The space for the buffers is reserved by the driver when the
machine is booted. For example:
/S 512
sets the buffer size to 512 bytes. The default size is 256 bytes.
Note that in actual operation only n-1 bytes are available, so the
default buffer, nominally 256 bytes long, can only hold 255 bytes.
DOS Installation

Chapter 4 Page 45