On Tue, 28 Aug 2012 04:04:20 -0400 (EDT), Stan Hoeppner wrote: > Stephen Powell wrote: >> By the way, there's something I don't understand. A 32-bit processor can >> only access 4G of "real" (extended) memory, right? So why are there >> motherboards available for 32-bit processors that support installing >> more than 4G of RAM? What good is memory that the processor can't address? > > The processor can address up to 64GB using PAE: > http://en.wikipedia.org/wiki/Physical_Address_Extension
That explains it. Thanks. Thanks also to the other members of the list who responded regarding PAE. > > ... > Note I used the word mainframe. All of this unique technology and > scalability Unisys brought to x86, MS Windows and, to a lesser degree, > Linux, was directly derived from Unisys' ClearPath mainframe technology, > where such features had been common for years, as well as on IBM, > Fujitsu, and other mainframes. > ... I work on IBM mainframes as my "day job". 32-bit IBM mainframes have a 2 GB address limit. (That's because, although the registers for manipulating binary integer numbers are 32-bits wide, the address bus has only 31 address lines.) Physical memory in excess of 2 GB could be installed though. You could use the extra memory in two ways. (1) IBM provides virtual-machine-level virtualization built-in to the hardware microcode, known as PR/SM (Processor Resource / System Manager). This can create what are known as LPARs (Logical PARtitions). You can divide up the physical memory between LPARs, so that each LPAR does not exceed 2G. (2) You can configure some of the memory, either in basic mode or in LPAR mode, as "expanded memory". (Think back to the "expanded memory boards" in the days of DOS.) This in known in IBM lingo as XSTORE memory as opposed to CSTORE memory. Some IBM mainframe operating systems, such as VM, can use XSTORE memory as a high-speed paging device. Then, some applications, such as DB2, can use "hyperspaces" or "VM data spaces" as ways to exploit memory above 2 GB. I was aware of these techniques in the mainframe world to exploit memory above 2 GB, but I'm much less familiar with the world of PC CPUs. BTW, IBM's 64-bit machines no longer offer a "basic mode". LPAR mode is required on all 64-bit machines, AFAIK. -- .''`. Stephen Powell : :' : `. `'` `- -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/1943825377.705792.1346163449270.javamail.r...@md01.wow.synacor.com
