> mcclnx mcc wrote: > > we plan to setup our ORACLE database server (32 bits DB) and use dell > > r900 server. This server can put up to 128GB RAM. > > We are thinking use 32 bits CENTOS 4.7 or 5.2. My concern about > > CENTOS 5.2 is it only support up to 16 GB RAM on 32 bits O.S. > > Any suggestion? > To get beyond 4 GB of RAM with a 32-bit Intel CPU, you have to turn on > PAE mode, which is a very ugly hack, invented several years ago now. It > dates back to the old Pentium Pro! It was created before inexpensive > 64-bit CPUs were available. Systems being built today should not use > PAE mode, IMHO. If you need more than 4 GB of RAM today, use a 64-bit > OS and applications. That will let you address the full memory > capability of that server. > In PAE mode, the system runs a little slower due to the extra overhead > of the more complicated memory management scheme, and it can't really > address that 16 GB all at once. It's kind of a like the old DOS days > when we had 32-bit CPUs but could only address 64 KB of memory at a > time, and could only access 640 KB without resorting to PAE-like hacks > called EMS and XMS. These workarounds are best consigned to the dustbin > of history. Not true. The comparison of PAE to EMS/XMS is completely bogus, the technologies aren't alike at all. PAE does *NOT* involve any bank switching; a system using PAE can "address that 16 GB all at once". Comparing PAE to EMS/XMS has the same level of validity as comparing a .NET or Java virtual machine to a shell script interpreter. <http://en.wikipedia.org/wiki/Physical_Address_Extension#Page_table_structures> There is a, usually very small, performance penalty to PAE due to the using a three level verses a two level page directory.