KfWiki: Memory

Memory

Obviously, the big question about memory is whether 32bit OS can support memory size of 4G and/or above. My machine is recently upgraded to 4x1G DDR2-800, let's see how many was recognized by various OS'es.

Testbed

Motherboard: Gigabyte P35-DS3L Bios F6 (Support up to 4G memory)
CPU: Intel C2D 6850
Memory: SuperTalent DDR2-800 CL4 1G x4

Fedora Core7 64bit

Needless to say, all 4G is usable.

# free -m
			 total       used       free     shared    buffers     cached
Mem:          3968       1008       2960          0         22        450
-/+ buffers/cache:        535       3433
Swap:         1953          0       1953

Interpreting free

A side topic to this is how to interpret free. Linux uses spare memory to cache I/O operations. Using the above example, 535M is in use by application, 3433M is actually free. This seems to apply to kernel 2.4 only. Ref http://rimuhosting.com/howto/memory.jsp

Ubuntu 7.10 Desktop 32bit, kernel 2.6.22-14-generic

Well.. only 3.5G even dmesg says PAE has been enabled & dmidecode sees all 4G of memory modules.

# free -m
			 total       used       free     shared    buffers     cached
Mem:          3546        605       2940          0         86        344
-/+ buffers/cache:        174       3371
Swap:         1953          0       1953

Knoppix 5.1.1 2007-01-04 32bit, kernel 2.6.19

Same

# free -m
			 total       used       free     shared    buffers     cached
Mem:          3549        302       3247          0          8        152
-/+ buffers/cache:        141       3408
Swap:            0          0          0

I even passed the mem=4096m parameter to kernel, in vain

# cat /proc/cmdline
ramdisk_size=100000 ...boring... mem=4096m

Windows XP sp2 32bit

Boot.ini

[boot loader]
timeout=15
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /NoExecute=OptIn /PAE
C:\CMDCONS\BOOTSECT.DAT="Microsoft Windows Recovery Console" /cmdcons

msinfo32 was able to recognize all 4G of memory

OS Name	Microsoft Windows XP Professional
Version	5.1.2600 Service Pack 2 Build 2600
Hardware Abstraction Layer	Version = "5.1.2600.2180 (xpsp_sp2_rtm.040803-2158)"
Total Physical Memory	4,096.00 MB
Available Physical Memory	2.71 GB
Total Virtual Memory	2.00 GB
Available Virtual Memory	1.96 GB

BUT no surprises there, even with PAE enabled, Windows is only able to use 3.5G of memory. I guess I'm the lucky one already, some see even less than that.

KfWiki : Memory