Mainframe, MVS and zOS Discussion

What is a Word? Half-word? How many bytes are there in one word?

In computing, "word" is a term for the natural unit of data used by a particular processor design. The mainframe "was" originally a half-word, full-word and double-word centric system.

Said that - A full-word is four bytes in length, a double-word is eight bytes long and a half-word is two bytes long.

Hope this helps.

So the memory will always "swap" only words and not "bits" of information?

If you are talking about memory swaps (such as paging to / from auxiliary storage), the unit used is a page. And a page is 4096 bytes (4KB or 1024 words).

Thanks Robert (and Sandy). I look at other post of yours Robert - that also helps.

An update to my previous answer: z/OS now supports large frames for handling memory objects in the 64-bit address space (above the bar). Large frames are referenced in 1 megabyte (1,048,576 bytes) increments and are NOT paged with the older 4K pages.