[CentOS] 4gb ram shows as 3.3gb

Martin Marques martin at bugs.unl.edu.ar
Thu Jul 26 21:37:44 UTC 2007

John R Pierce wrote:
> but thats neither here nor there, PAE is a universal issue for any x86 
> 32bit system with 4GB+ ram, with PAE disabled, the BIOS, PCI, AGP or 
> PCI-express, etc IO spaces consume anywheres from .5 to 1GB of the 32bit 
> address space.   PAE is a hardware workaround implemented in pretty much 
> all Intel and AMD CPUs made in the last 5+ years, and allows the OS to 
> access more than 4GB of physical address space.  PAE introduces some 
> hardware overhead because it involves larger page tables and another 
> level of indirection in the TLB lookups.
> CentOS 5 installs defaults to PAE off because there are some systems 
> where PAE is crash-happy.    Someone here has already explained how to 
> enable PAE and in fact the original poster tried it and is happy with 
> his full 4GB now.

Well, looks like I'm having quite a bit of a problem then. :-(

I have PAE kernel running, and all I see is 3.2Gb of the 4Gb.

dmidecode gives me this (intel chip):

Handle 0x0000, DMI type 0, 20 bytes.
BIOS Information
         Vendor: Intel Corp.
         Version: EV91510A.86A.0482.2006.0222.2350

And later this:

Handle 0x0041, DMI type 19, 15 bytes.
Memory Array Mapped Address
         Starting Address: 0x00000000000
         Ending Address: 0x000C77FFFFF
         Range Size: 3192 MB
         Physical Array Handle: 0x0040
         Partition Width: 0


Handle 0x0048, DMI type 17, 27 bytes.
Memory Device
         Array Handle: 0x0040
         Error Information Handle: 0x003F
         Total Width: 64 bits
         Data Width: 64 bits
         Size: 1024 MB
         Form Factor: DIMM
         Set: 2
         Locator: J6H2
         Bank Locator: CHANNEL B DIMM1
         Type: DDR
         Type Detail: Synchronous
         Speed: 400 MHz (2.5 ns)
         Manufacturer: Manufacturer4
         Serial Number: SerNum4
         Asset Tag: AssetTagNum4
         Part Number: PartNum4

Handle 0x0049, DMI type 20, 19 bytes.
Memory Device Mapped Address
         Starting Address: 0x000C0000000
         Ending Address: 0x000C6FFFFFF
         Range Size: 112 MB
         Physical Device Handle: 0x0048
         Memory Array Mapped Address Handle: 0x0041
         Partition Row Position: 2
         Interleave Position: 2
         Interleaved Data Depth: 2

As you can see, the last 1Gb bank is only used at 11%.

Any ideas on why I can't see all 4Gb?

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