Mainframe, MVS and zOS Discussion

Hi,

Why it is called "the line"? I've read some dialogues on assembler and cobol in which they talk about "above the line" or "below the line"... what does it signifies? And how this come to the usual conversations?

The original S/360 systems could only use 24-bit addresses. Over time as systems got bigger, this started to become an issue. IBM addressed the issue by allowing 31-bit addresses (the 32nd bit in the 4-byte word was used to designate which was being used). Since a 24-bit program couldn't use 31-bit addresses, the line became the term to distinguish the addressing modes. Above the line means 31-bit addressing, below the line means 24-bit addressing.

Now with 64-bit systems, there is also a bar between 31-bit addresses and 64-bit addresses.