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eddie0uk 03-11-2005 02:33 AM

4GB RAM not showing

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


# 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,



# 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


# 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)

slacky 03-11-2005 07:58 AM

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

eddie0uk 03-11-2005 09:22 AM

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

Ravo 03-11-2005 07:52 PM

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?

reddazz 03-12-2005 04:23 AM

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

eddie0uk 03-12-2005 08:08 AM

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.

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