RAM differences

Troy Hakala troy at recipezaar.com
Fri Apr 14 15:05:13 CDT 2006


We just bought a Dell PowerEdge 850 to test Dells versus our current  
vendor's hardware. The other machine has a Supermicro PDSMi  
motherboard. Both machines have 4GB RAM.  /proc/meminfo on the  
Supermicro machine reports 3.7GB and the Dell reports 3.1G.

The BIOS map from dmesg on both machines are shown below. I don't  
understand exactly what it means but it seems that the Dell's BIOS  
breaks up the memory differently and as a result, linux can't see the  
extra 600MB (the numbers in parentheses after each map section were  
added by me to show total memory in each map area). Notice that the  
Supermicro breaks the usable memory into 3 pieces of 640k, 3.8G and  
402M while the Dell breaks it into 3 pieces of 640k, 3.2G and 1G. The  
difference between the 3rd pieces in both is the difference in total  
RAM according to /proc/meminfo (and free).

Why? Can it be fixed by fiddling with the Dell's BIOS settings?


Supermicro:
-----------------
Linux version 2.6.15-1-686-smp (Debian 2.6.15-8) (waldi at debian.org) (gcc
version 4.0.3 20060212 (prerelease) (Debian 4.0.2-9)) #2 SMP Mon Mar  
6 15:34:50
UTC 2006
BIOS-provided physical RAM map:
  BIOS-e820: 0000000000000000 - 000000000009d000 (usable)    (640k)
  BIOS-e820: 000000000009d000 - 00000000000a0000 (reserved)
  BIOS-e820: 00000000000ca000 - 00000000000cc000 (reserved)
  BIOS-e820: 00000000000e4000 - 0000000000100000 (reserved)
  BIOS-e820: 0000000000100000 - 00000000e7ee0000 (usable)    (3.8G)
  BIOS-e820: 00000000e7ee0000 - 00000000e7ee9000 (ACPI data)
  BIOS-e820: 00000000e7ee9000 - 00000000e7f00000 (ACPI NVS)
  BIOS-e820: 00000000e7f00000 - 00000000e8000000 (reserved)
  BIOS-e820: 00000000fec00000 - 00000000fec10000 (reserved)
  BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
  BIOS-e820: 00000000ff000000 - 0000000100000000 (reserved)
  BIOS-e820: 0000000100000000 - 0000000118000000 (usable)    (402M)
Warning only 4GB will be used.
Use a PAE enabled kernel.
3200MB HIGHMEM available.
896MB LOWMEM available.
found SMP MP-table at 000f5f40
On node 0 totalpages: 1048576
   DMA zone: 4096 pages, LIFO batch:0
   DMA32 zone: 0 pages, LIFO batch:0
   Normal zone: 225280 pages, LIFO batch:31
   HighMem zone: 819200 pages, LIFO batch:31


Dell:
-----------------
Linux version 2.6.15-1-686-smp (Debian 2.6.15-8) (waldi at debian.org) (gcc
version 4.0.3 20060212 (prerelease) (Debian 4.0.2-9)) #2 SMP Mon Mar  
6 15:34:50
UTC 2006
BIOS-provided physical RAM map:
  BIOS-e820: 0000000000000000 - 00000000000a0000 (usable) (640k)
  BIOS-e820: 0000000000100000 - 00000000bffc0000 (usable) (3.2G)
  BIOS-e820: 00000000bffc0000 - 00000000bffcfc00 (ACPI data)
  BIOS-e820: 00000000bffcfc00 - 00000000bffff000 (reserved)
  BIOS-e820: 00000000e0000000 - 00000000fed00400 (reserved)
  BIOS-e820: 00000000fed13000 - 00000000feda0000 (reserved)
  BIOS-e820: 00000000fee00000 - 00000000fee10000 (reserved)
  BIOS-e820: 00000000ffb00000 - 0000000100000000 (reserved)
  BIOS-e820: 0000000100000000 - 0000000140000000 (usable)   (1G)
Warning only 4GB will be used.
Use a PAE enabled kernel.
3200MB HIGHMEM available.
896MB LOWMEM available.
found SMP MP-table at 000fe710
On node 0 totalpages: 1048576
   DMA zone: 4096 pages, LIFO batch:0
   DMA32 zone: 0 pages, LIFO batch:0
   Normal zone: 225280 pages, LIFO batch:31
   HighMem zone: 819200 pages, LIFO batch:31



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