Since literals are write protected alteration is no longer permitted and the trap handler logic had to be revised. It should also be noted that, because of problems like the one mentioned above in the trap routine, pure procedure programs must use the shared library. A notable amount of library data area was saved by using much of the library context area as a scratch area. The data savings amount to about 0.52K words per user. See example in Figure 3 .
Language is necessary for a detailed description of how XROM works.
The altered PMAP is now added to the start address rather than the beginning data address. The prototype for XROM was finished in September 1978 and the XROM processor was completed in November 1978. A program was written to strip the LO listing of extraneous garbage to prepare the file for assembly. After an extensive search for additional rules to follow we had three versions of the prototype that were used to convert our first six programs. The only way to tell which version to use was to try one and if it did not work properly to try another version.