Ultrix problem

[Art Berggreen]

> I can't say that this is the absolute truth but the word that I've
> heard is that DEC is suspending shipments of Ultrix for the uVAX II
> due to some memory problem that affects low-memory.   As most UNIX
> hacks know, this is where the kernal resides.   This will also
> affect the uVMesS users as well but the "kernal" for VMesS is in
> high-memory while the user's code is in low.  Nicely enough, this is
> where the user code gets loaded and DEC figures that this is
> acceptable (to have the user code bomb due to h/w problems).

NOT TRUE!!!

Due to VAX hardware architecture, in both VMS and UNIX the kernel
VIRTUAL addresses start at 0x80000000 and user processes start at
0x00000000 with process data below 0x7fffffff (VMS and some UNIXs
make page 0 noaccess).  In both VMS and UNIX the kernel is loaded
into low PHYSICAL memory while user processes tend to run in higher
PHYSICAL pages.

The uVAX-II problem was apparently an obscure memory timing problem
which caused one manufacturer's parts to fail only with UNIX.  It
appears DEC has solved this and Ultrix shipments are resuming.

				"Art Berggreen"<Art at ACC.ARPA>

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