LinuxQuestions.org - 4GB RAM not showing

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4GB RAM not showing

Hi,

I have installed Linux (Ubuntu) in a machine with 4GB of RAM but the kernel (2.6.10) only see s 3.2GB:

Code:

# free

            total      used      free    shared    buffers    cached

Mem:      3245128    611896    2633232          0      7872    238256

-/+ buffers/cache:    365768    2879360

Swap:      2931820      2820    2929000

I have compiled the kernel several times, with 64gb support (just in case) as well as enabling HIGH_PTE but the result is the same. Appending "mem=4G" to ther kernel boot line does not help either. Does anybody have any ideas? Attached my /proc/meminfo and first lines of dmesg.

Many thanks,

Eduardo.

Code:

# cat /proc/meminfo

MemTotal:      3245128 kB

MemFree:      2632652 kB

Buffers:          7984 kB

Cached:        238416 kB

SwapCached:      2820 kB

Active:        471432 kB

Inactive:        99560 kB

HighTotal:    2357436 kB

HighFree:      1839168 kB

LowTotal:      887692 kB

LowFree:        793484 kB

SwapTotal:    2931820 kB

SwapFree:      2929000 kB

Dirty:              40 kB

Writeback:          0 kB

Mapped:        376476 kB

Slab:            21436 kB

CommitLimit:  4554384 kB

Committed_AS:  684724 kB

PageTables:      2220 kB

VmallocTotal:  114680 kB

VmallocUsed:    45548 kB

VmallocChunk:    68084 kB

Code:

# dmesg | head

Linux version 2.6.10-4-686-smp (buildd@mcmurdo) (gcc version 3.3.5 (Debian 1:3.3.5-8ubuntu2)) #1 SMP Wed Mar 2 06:29:34 UTC 2005

BIOS-provided physical RAM map:

 BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)

 BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)

 BIOS-e820: 00000000000e6000 - 0000000000100000 (reserved)

 BIOS-e820: 0000000000100000 - 00000000c7e2fc00 (usable)

 BIOS-e820: 00000000c7e2fc00 - 00000000c7e3fc32 (ACPI NVS)

 BIOS-e820: 00000000c7f10000 - 00000000c7f30000 (reserved)

 BIOS-e820: 00000000c7f30000 - 00000000c7f40000 (ACPI data)

 BIOS-e820: 00000000c7f40000 - 00000000c7ff0000 (ACPI NVS)

 BIOS-e820: 00000000c7ff0000 - 00000000c8000000 (reserved)

 BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)

 BIOS-e820: 00000000fed13000 - 00000000fed1a000 (reserved)

 BIOS-e820: 00000000fed1c000 - 00000000feda0000 (reserved)

Does the computer's BIOS report the installed RAM size anywhere?

Yes. The BIOS setup reports the 4GB. memtest also reports the 4GB.

If you have a 32 bit processor, all it can use is 3.2 gigs of RAM. That´s the physical limitation of it. IIRC. Perhaps Ubuntu is just ignoring that .8 gigs to save your processor the hassle.

Unless you´re making a uber-server, why would you need 4 gigs in the first place?

Yeah, 4 gigs is a lot of ram even for most small to medium sized x86 servers.

Thanks. I see this when booting the computer in the first screen:

Memory consumed by system resources: 898 MB System RAM

So I think there it is the answer. Also saw this in the DELL faqs:

BIOS must reserve some address space below 4GB for PCI devices such as RAID controllers, SCSI controllers, NICs, etc. RAID controllers in particular may request and be given 256MB each. This is address space that would normally be occupied by RAM, but instead is used by PCI devices.

RAM addresses start at 0 and grow up. PCI device addresses start at 4GB and grow down. As long as there is no overlap, the OS will see all available RAM and make use of it. If there is overlap, the PCI devices win, and that RAM is not made available to the OS.

This is working as designed per PCI, BIOS, and system chipset specifications.