Z61P with 2 SO-DIMMS of 2 GB each only sees 3 GB

[dado1981]

Hi,

I have installed two 2 GB DIMMs (5300S 667 MHz, if I'm not mistaken) to my laptop Z61p, and upgraded to the latest BIOS.
BIOS (eg. when I press the blue ThinkPad key) correctly reports 4096 MB of RAM installed.
But my OS, currently latest Linux Mint, and that is the x86-64 version (uname -a confirms that) only sees 3 GB... That is to be expected on the 32-bit OS, but not on 64-bit.
Maybe it's some kernel thing, I might try some live distros to see if different kernels affect this, but genneraly, does this laptop supports 4 GB at all? BIOS in it definately does. Maybe some hidden BIOS setting? Do you have ideas?

Thanks for your help.

[Neil]

It's a chipset limitation on the T60 and Z61 series machines. Makes no difference what OS is being used, whether 32 or 64bit. At least with 2x2GB, you will see a slight benefit from using dual channel mode compared to having 3GB physically installed.

[dado1981]

It's a chipset limitation on the T60 and Z61 series machines. Makes no difference what OS is being used, whether 32 or 64bit.

OK, thanks.
It is interesting that the BIOS sees all 4 GB.
On the side note, does anyone knows why this is like that? I know memory of various hardware devices has to be mapped somewhere in (virtual) memory, so the OS drivers and/or other software could have a means to access and manipulate the memory of a hardware devices... That in turns invalidates part of physical RAM on 32bit systems even with 4 GB RAM, as the memory-mapped part has to be in 0-4G range because of 32bit integer size limit. But the limit on 64bit system for address space (pointer to the memory address) is way more than than that 4G...

[dr_st]

The chipset on these machines has a 32-bit word size limit.

[dado1981]

The chipset on these machines has a 32-bit word size limit.

Thank you,

[censored], there goes 1 GB of wasted money . I guess I will now sell one of these 2 GB DIMMs and put one 1 GB original DIMM back, to have 3 GB of physical RAM, as it will obviously not make any difference...

Edit: didn't know that D.A.M.N is a banned word on these forums. It is really not that ugly of a word

[underclocker]

As mentioned by Neil above, using two matched memory sticks, like 2 x 2GB or 2 x 1GB, actually improves overall performance by about 5%, for memory intestive tasks. So, keeping both 2GB sticks installed may be worth it.

More dual channel mode info --> http://en.wikipedia.org/wiki/Multi-chan ... chitecture

[dado1981]

As mentioned by Neil above, using two matched memory sticks, like 2 x 2GB or 2 x 1GB, actually improves overall performance by about 5%, for memory intestive tasks. So, keeping both 2GB sticks installed may be worth it.

More dual channel mode info --> http://en.wikipedia.org/wiki/Multi-chan ... chitecture

Thank you so much for this info, I didn't know that...