> 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, thetechnologies aren't alike at all. PAE does *NOT* involve any bankswitching; a system using PAE can "address that 16 GB all at once".Comparing PAE to EMS/XMS has the same level of validity as comparinga .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 theusing a three level verses a two level page directory.
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