Mainframe, MVS and zOS Discussion

Hi,

What is the difference between "Refactor and Rehosting" - are they not just part of same coin?

They can be the same or they can be different. Refactoring is taking existing code and doing things to it (such as modularizing the code or moving common functions into subprograms). Re-hosting is moving the code to a different platform; depending upon the language used and the platforms, the re-hosting may not require any code changes.

Can mainframe application be re-hosted and work? There are a lot of documentation about re-hosting on AWS https://aws.amazon.com/mainframe/#:~:te ... 0as%20Java. They all sound too promosing to be good. What factors can one start looking for such re-platforming of a mainframe application? Any thoughts you would want to share on that?

Mainframe applications are not typically good candidates for re-hosting, since mainframes use EBCDIC whereas most other platforms use ASCII. This incompatibility can introduce subtle bugs since the collating sequences are different; if the application depends upon numbers sorting after letters, that is an EBCDIC dependency. ASCII sorts numbers BEFORE letters.

At a previous employer, I moved an application from a mainframe to a PC using GNU COBOL running in CYGWIN. The application was kept the same as far as files and sorts, and there weren't really any issues with CYGWIN. The application was moved due to the mainframe being eliminated. On the mainframe, the application had 4 job streams doing monthly updates that ran for a total of about 3 hours elapsed. On the PC, the application took 2 8-hour days to perform the monthly update as there were a number of 400-million-byte files to read / write / sort.