Editing IBM PALM processor (section)

== Executive ROS Extraction ==

Because executable ROS cannot be read as data from a running PALM program (see [[#Card Complement Around PALM|Card Complement]] above), reverse-engineering the executive ROS required exploiting a hardware feature of the 5100 / 5110 boot sequence:

# On the very first machine cycle after power-on, the display adapter shows the 512 bytes of executive ROS at whatever address the SAB jumpers point to (default 0x0000).
# The internal '''Single-Step switch''' (accessible through the case via two screws) lets the field engineer freeze the machine on that first cycle.
# Pulling the SAB jumpers to different addresses lets you walk through all 128 × 512-byte = '''64 KB pages''' of executive ROS, photographing each frozen frame.

Christian Corti applied this to the '''5110''' between 2007 and 2012, photographing every page at high resolution and OCR-ing the result.

'''Tom Stepleton and Corti''' repeated the procedure on a '''5100''' in January 2019, using AI-guided OCR followed by manual correction. The full project notebook is at `github.com/stepleton/5100ExecutableROSDecode`; the decoded ROS images are archived at `archive.org/details/ibm_5100_ros`.

The non-executable ROS — APL on C2 / D2 / D4 (5100) and BASIC on C4 — is extracted in software, not by display-trickery, because it is reachable as an I/O device. A small PALM program written via the Diagnostic Control Program loops `CTL DA=1, #$04 ; PUTB-addr ; GETB-data` to dump non-executable ROS into RWS, then a DCP-driven RWS-to-disk dump and a KERMIT transfer to a modern host completes the extraction. The full DCP listing is documented by Corti at the Stuttgart Computer Museum's "Extracting the non-executable ROS" page.