Re: z/Architecture?

Paul Edwards

On Sun, Oct 24, 2021 at 06:44 AM, Joe Monk wrote:

"Patents only last 20 years. So long as you aren't using any
functionality that didn't exist in the first version of z/Arch,
you can do whatever you want."

Every time they come out with a new model of z/box, its a new patent
For any new functionality, yes. So long as you stick to the
original functionality that is more than 20 years old, IBM
has no case against you. That's the whole point of the
expiry date. Otherwise at the 19 year mark, people could
just paint their invention a new color and say the patent of
the old version, even with the old color, is renewed for
another 20 years too.

"get the 4 GiB
to 8 GiB virtual address space mapped on to 0 - 4 GiB real

DAT doesnt work that way.

z/Arch memory in DAT is broken into 3 parts: a region (2GB), a segment
(1MB), and a page (4KB). You cant just "map 4-8 GB on 0-4 GB)". Every
memory page in z/arch will have an address. DAT will fixup the page
addresses at demand time. So there's no 1:1 mapping between a real memory
address and a DAT address - memory is paged in/out in 4KB chunks.
I'm talking about creating page tables so that every 4KB chunk
in the 4 GiB to 8 GiB region is mapped to 0 GiB to 4 GiB.

BFN. Paul.

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