Version 12.1 provides enhanced Journaling for Dyalog APL component files and includes the facility to check sum components.
The latter is highly recommended as it enables component files to be repaired using the new system function ⎕FCHK. However, component files written with Checksum enabled cannot be read by versions of Dyalog APL prior to Version 12.1.
In addition to the level of Journaling provided in Version 12.0 (now called Level 1 Journaling), two further levels are introduced.
Level 2 journaling provides protection not just against the possibility that the APL process terminates abnormally, but that the Operating System itself fails. However, a damaged component file must be explicitly repaired using the new system function ⎕FCHK which will repair any damaged components by rolling them back to their previous states.
Level 3 provides the same level of protection as Level 2, but following the abnormal termination of either APL or the Operating System, the rollback of an incomplete update will be automatic and no explicit repair will be needed.
Higher levels of Journaling inevitably reduce the performance of component file updates.
For further information, see ⎕FPROPS and ⎕FCHK.