home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!haven.umd.edu!decuac!pa.dec.com!nntpd2.cxo.dec.com!nntpd.lkg.dec.com!sousa.ltn.dec.com!vssad!dormitze
- From: dormitze@vssad.enet.dec.com (Paul Dormitzer)
- Newsgroups: comp.sys.dec
- Subject: Re: VAX question (P0/P1 space)
- Message-ID: <1397@sousa.ltn.dec.com>
- Date: 27 Jul 92 21:24:48 GMT
- References: <1992Jul26.015003.1@matrix.cs.wright.edu> <1992Jul26.211939.25698@prl.dec.com> <MOSS.92Jul26183952@ibis.cs.umass.edu>
- Sender: newsa@sousa.ltn.dec.com
- Reply-To: dormitze@vssad.enet.dec.com (Paul Dormitzer)
- Organization: Digital Equipment Corporation
- Lines: 29
-
-
- In article <MOSS.92Jul26183952@ibis.cs.umass.edu>, moss@cs.umass.edu (Eliot Moss) writes:
- |>
- |>3) Kernel space is the third quarter of the address space, as previously
- |>noted, and is generally shared among all processes (but pages have different
- |>protections in user, exec, supervisor, and kernel modes, so this is safe,
- |>etc.)
- |>
-
- This is S0 space.
-
- |>4) The fourth quarter of the address space is generally used for I/O devices
- |>and could be called "I/O space", though I am not sure if that is an "official"
- |>designation.
- |>
-
- Here you're confusing the high-address physical address space and virtual
- address space. The high-address physical addresses are indeed I/O space, but
- the high-address virtual addresses are S1 space, which has been "reserved for
- future expansion" in most VAX implementations, and was finally defined as an
- extension of S0 space to double the system vitrual address space in the newest
- VAX implementations.
-
- As a side note, not all operating systems use the virtual address regions the
- same way. VAXELN uses an interesting partition of the three available
- address spaces. S0 is shared by all jobs in the system, P1 is shared by all
- processes in a job (but not between jobs), and P0 is private to each process.
-
- Paul
-