Editing CP/M (section)

=== Resident programs ===

CP/M originally did not support the equivalent of [[terminate and stay resident]] (TSR) programs as under DOS. Programmers could write software that could intercept certain operating system calls and extend or alter their functionality. Using this capability, programmers developed and sold auxiliary [[desk accessory]] programs, such as [[SmartKey]], a keyboard utility to assign any string of bytes to any key.<ref name="Software_Catalog_1984"/>
CP/M&nbsp;3, however, added support for [[dynamic loading|dynamically loadable]] ''Resident System Extensions'' (RSX).<ref name="CPM3_1983_PG"/><ref name="Brown-Strutynski-Wharton_1983"/> A so-called ''null command file'' could be used to allow CCP to load an RSX without a transient program.<ref name="CPM3_1983_PG"/><ref name="Brown-Strutynski-Wharton_1983"/> Similar solutions like RSMs (for ''Resident System Modules'') were also retrofitted to CP/M&nbsp;2.2 systems by third-parties.<ref name="ct_1"/><ref name="ct_2"/><ref name="Huck_2016"/>