Virt Mem on V.4

[paul.ho]

> With any luck, all you'll have to do is write a "hat (Hardware Address
> Translation) layer" for your MMU, which'll just plug into the rest of
> the VM subsystem.  (If the new hardware uses a 68020+PMMU, or a 68030 or
> so - i.e., if it's using a Motorola-style MMU - you might just see if
> Sun'll sell you their 4.0 implementation; I have no idea if they will,
> but it's worth a try....)  If you *do* have to do more, let AT&T (and
> possibly Sun) know, so that with any luck the implementation can be
> modified to let the new "hat layer" plug into it in the future.

Is region (introduced in SVR3.0) dead? Or does it co-exist with
the VM stuff in SVR4? Thanks.