wilson@carcoar.Stanford.EDU (Paul Wilson) (09/07/89)
I'm looking for a cheap hardware platform that will run Mach with
a small page size. I'm considering a microVAX, but something with
a better price/performance ratio would be nice. I can get a MacII
pretty cheap.
Does anybody know offhand the page size on the MacII? My understanding
is that the MC68851 can handle any page size that's a power of 2 multiple
of 512 bytes; the choice of page size is up to the system designer.
My source for this little tidbit (BYTE) doesn't specify whether this
means the hardware designer or the OS designer. I suspect it's the
former because page size choice often interacts with cache design
considerations. So anyway, if the page size is fixed in hardware,
what is it? And if not, how small a page can I get with Mach?
(Oh yeah -- Apple has its own propriety PMMU that's a subset of the
68851 -- maybe that fixes the page size, at least for some MacII's?)
thanks prematurely,
Paul
Paul R. Wilson
Software Systems Laboratory lab ph.: (312) 996-9216
U. of Illin. at C. EECS Dept. (M/C 154) wilson@bert.eecs.uic.edu
Box 4348 Chicago,IL 60680
Paul R. Wilson
Software Systems Laboratory lab ph.: (312) 996-9216
U. of Illin. at C. EECS Dept. (M/C 154) wilson@bert.eecs.uic.edu
Box 4348 Chicago,IL 60680 robertl@bucsb.UUCP (Robert La Ferla) (09/08/89)
In article <11682@polya.Stanford.EDU> wilson@carcoar.Stanford.EDU (Paul Wilson) writes: > >I'm looking for a cheap hardware platform that will run Mach with >a small page size. I'm considering a microVAX, but something with >a better price/performance ratio would be nice. I can get a MacII >pretty cheap. The NeXt machine runs MACH. Check out comp.sys.next.
daveh@cbmvax.UUCP (Dave Haynie) (09/08/89)
in article <11682@polya.Stanford.EDU>, wilson@carcoar.Stanford.EDU (Paul Wilson) says: > Keywords: Mach, Macintosh II, page size, virtual memory, PMMU, 68851 > Xref: cbmvax comp.sys.mac:41273 comp.os.mach:45 > Does anybody know offhand the page size on the MacII? My understanding > is that the MC68851 can handle any page size that's a power of 2 multiple > of 512 bytes; the choice of page size is up to the system designer. You can set the minimum page size between 256 bytes and 32k, in power of 2 increments, for both 68851 and 68030 MMUs. That's the minimum page -- since the MMU reads a translation tree, larger effective page sizes are no problem; the tree can terminate at any level. The 68030 also provides two registers for transparent translation, useful for I/O spaces or other non-translated space that you'd rather not work into your MMU tables. > So anyway, if the page size is fixed in hardware, what is it? If you're upward looking on such a system, it's probably better to think in terms of 4k or 8k pages; the 68040 MMUs are limited to those two sizes. > (Oh yeah -- Apple has its own propriety PMMU that's a subset of the > 68851 -- maybe that fixes the page size, at least for some MacII's?) Far as I know, the Apple MMU does two things: [1] Wraps the 32 bit address into 24 bits so that native Mac OS stuff works, and [2] holds the place that the 68851 will go. It doesn't really page or anything; they require a 68851 to support any sort of translation (UNIX) or even virtual memory under the Mac OS. > Paul -- Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy Too much of everything is just enough