Extended Addressing

This interoffice memorandum, written by Mike Uhler in 1983, serves to formalize documentation for extended addressing in the PDP-10 architecture, specifically addressing deficiencies found during the development of EBOX microcode for the Jupiter processor.

Key contents include:

• Definitions: Standardizes terminology such as virtual, local, and global addresses, as well as various address word and index formats (IFIW, EFIW, local/global).
• Effective Address Calculations (EA-calc): Provides detailed rules and examples for computing effective addresses, emphasizing how indexing and indirection behave in local vs. global contexts.
• Special Instructions: Describes how specific instructions (e.g., Byte instructions, EXTEND, JSP/JSR, Stack operations, BLT, XBLT, JSA/JRA, LUUOs, XCT) are modified to support extended addressing.
• Previous Context (PXCT): Explains the PXCT mechanism, which allows the monitor to make references to a previous context's memory and ACs, including modification of the EA-calc algorithm and usage of control bits in the AC field.

The memo is intended as a definitive reference for developers and was meant to be incorporated into the Processor Reference Manual (PRM).