I think the gist of the original mail was which systems ARE out there which DO support this. A lot of systems get produced which, for various reasons, can't support more than 4GB because they simply didn't make memory modules big enough.
These days a 4GB memory module is all you can go up to (at standard DDR PC2100 specs) so the maximum real memory configuration you could get for each bank of memory is 4GB. Board sizes dictate how much memory you can really have. I think some boards my Mercury may have supported large memory sizes, but they are hardly "common" or due to run OpenSolaris :) In theory any G4-class processor (7400, 744x, 745x) supports 36-bit physical memory addressing, not just the "sevens". Ideally supporting it is as troublesome as on any other system though (Intel's PAE is directly comparable) on a 32bit OS. I think it's only really suitable to more "specialised" applications. Does Linux really support it? It barely supports PAE (and has the same "kernel hacks" as Windows for having a 2GB/2GB kernel/user split or a 1GB/3GB for larger apps). At least on both systems the available memory for apps is defined by the space between the kernel space and PCI space, which is 3GB or less anyway. It doesn't give any ONE application any better use of the memory, but may give many applications (perhaps database connections) a little more headroom. The experience under PAE is that the MMU handling required has a significant overhead to it which negates the benefit of having more memory in the first place. You get the ability to handle a much larger database, more slowly. The PowerPC method seems a little better thought out, and at least has a lot less overhead, but the actual result may be the same underwhelming benefits. On systems which have been historically produced to take advantage of these addressing extensions they have been very specialised for one app (like a database) and the database has been specially written to take advantage of it. Like Sven said, the Pegasos II supports 2GB but there is nothing to stop you putting two 4GB (PC2100) modules in there if we let you (the firmware currently refuses to configure it). One better solution than mapping it as memory, is to use it as chipset support as huge amounts of DMA buffers or suchlike. -- Matt Sealey <matt at genesi-usa.com> Manager, Genesi, Developer Relations > -----Original Message----- > From: powerpc-discuss-bounces at opensolaris.org > [mailto:powerpc-discuss-bounces at opensolaris.org] On Behalf Of Ken Mays > Sent: Friday, January 06, 2006 6:37 PM > To: powerpc-discuss at opensolaris.org > Subject: [powerpc-discuss] New PowerPC e600-based processors > > > The MPC7447-MPC7457 handle 4GB-64GB RAM. The MPC603e handles 4GB RAM.
