IBM 5155 - Page 330

Specific Instructions
The system board of the IBM Portable Personal
Computer comes standard with 256Kof total memory.
You can only install the memory modules
on a
64/256KB Memory Expansion Option.
To install the modules
on the 64/256KB Memory
Expansion Option,
go to the Option Instructions that
came with that option.
2 64KB Memory Module Kit
January 1984