A short answer is so the hardware knows to use the 64-bit address in the 64-bit register instead of just the last 31-bits (AMODE-31).
On 2020-11-24 9:38 a.m., Rupert Reynolds wrote:
Reading (a lot of) documentation from IBM it seems that a lot has gone into the *nix side of z/OS and extra instructions and 64-bit addrssability for data, but that the code itself still resides below the bar, so that most AMODE 24 and 31 code from years ago will still compile/assemble and run as is, or with minimal change. Is that fair? But if new code using 64-bit data is still loaded and executed below the bar, and new instructions and extended registers handle the addressing of data with 64-bit addresses, why is there an AMODE 64 at all? Is it simply to indicate that a larger (DS 18D) savearea should be provided, as it may be needed by the called program? Thanks for any clarification you can offer. Roops
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