IBM 5150 PC Technical Reference (6025005, August, 1981) (PDF)

Switch - Configurable Start Address
Each card has a small DIP Module which contains eight switches. The
switches are used to set the card start address as follows:
Table 20. DIP Module Start Address
NO.
DESCRIPTION
1 ON: A19=O; OFF: A19=1
2 ON: A18=O; OFF: A18=1
3 ON: A17=O; OFF: A17=1
4 ON: A16=O; OFF: A16=1
5 ON: A15=O; OFF: A15=1 *
6 Not Used
7 Not Used
8 Used Only In 64KB RAM Card *
* Switch No.8 may be set on the 64KB Memory Expansion Option to use only half the
memory on the card (i.e., 32KB). If Switch No.8 is ON, all 64KB is accessible. If Switch
No.8 is 0 F F, address bit A15 (as set by Switch No.5) is used to determine wh ich 32KB
are accessible and the 64KB option behaves exactly like a 32KB option.
2-115