zero-one

Hiya

I have a Dell XPS 600. I took out the RAM that came with it (4 x 512mb DDR2 677) and replaced it with 2 x 1GB DDR2 800. I have now added 2 extra 1 GB sticks (same brand/model). The BIOS recognising that there is now 4GB of RAM but Windows doesn't. I ran Everest and it told me there was only 2GB.

I'm on a new install (after the 4GB of RAM installation) of Windows Vista.

The motherboard model is Dell DXG015.

The RAM is OCZ DDR2 800.

1 g0t 0wn3d

4GB of memory installed but only 3GB is showing in Windows.
Does this sound familiar?

Many people have noticed that when they install large amounts of memory in their systems, that Windows will show much lower then the actual physical amount. This is basically a limit of the 32 bit OS. Example: you install 4GB of memory. The system BIOS will show 4 GB of memory but the Windows OS only shows 3.25GB of memory.

Windows XP 32 bit version will accept up to 4GB of memory. However Windows will reserve the address space 3.5GB to 4GB to hardware devices. If these devices need more memory, Windows will allocate more of it to accommodate it. It is rare but not uncommon to see a system with 4GB of memory installed and only 2.75GB that is usable. Another note PCI-E 16x usually will gobble up 256MB of the address space. So if you have an SLI configuration, the 2 PCI-E 16x cards will chew up 512MB on top of the other devices that need the address space. It is possible to tweak the BIOS to reduce the amount of memory these devices use but often the result is negligible.

This is a note taken from an Intel MB manual:
ftp://download.intel.com/support/mot.../sp2gp2tps.pdf

Note: Memory between 4GB and 4GB minus 512MB will not
be accessible for use by the operating system and may be lost
to the user, because this area is reserved for BIOS, APIC
configuration space, PCI adapter interface, and virtual video
memory space. This means that if 4GB of memory is installed,
3.5GB of this memory is usable. The chipset should allow the
remapping of unused memory above the 4GB address, but
this memory may not be accessible to an operating system that
has a 4GB memory limit.

You can have more than 4GB on Windows XP 32 bit by using the PAE or Physical Address Extension switch and it may show in Windows, however the OS is still limited by 4GB and any memory installed above that will not be usable.

One must realize this is not a hardware issue but an operating system issue. These limits are not in the 64 bit versions of XP or Vista. Even the 32 bit version of Vista will have this limitation.

Also note that any application running in Windows XP 32bit is limited to 2GB and will not address anything above 2GB. This is lifted in 64bit, however if you are running a 32bit application in a 64bit OS, you still have the 2GB limit.

More information.

http://dlsvr01.asus.com/pub/ASUS/mb/4GB_Rev1.pdf
__________________
By craxijoe

zero-one

Cheers for the reply.

Sadly not the problem though. It only shows total physical 2.0gb and free physical 1.6 ish.

1 g0t 0wn3d

What does task manager say you may have got high density and not low so the high does not work (this one is again by crazijoe)
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There seems to be a lot of confusion with understanding high density and low density memory modules. I will try and clear this up a little.
A lot of people can obtain high density memory for a ‘cheap’ cost. These as usually branded as generic or do not have a brand name on them. While they save money on this memory, it may not work with their specific motherboard. A majority of motherboards do not accept high density modules. They usually show or register as half of what they spec out or advertised to be (i.e. bought a 1GB module and it only shows as 512MB), or they don’t work at all. This is common on all size modules. DDR and standard SDRAM included.

First rule, Double sided memory is not always low density modules. High density modules can have 16 chips (8 on each side). 'Standard' RAM chips are organized a DEPTH x 8 Bits. E.g. 32x8, 64x8, etc. That means 8 of the chips make up a 64 bit wide rank (memory bus is 64 bits wide). "Double Sided" is an old term to describe a stick with 16 chips, 8 on each side. And with DEPTH x 8 chips that makes for 2 ranks (or, again in an older style terminology: 2 'banks').

'High Density' chips are DEPTH x 4 bits so it takes 16 to make a 64 bit wide memory rank. And this is why "double sided" is no longer the favored description because when x8 chips are used "Double sided" means "double rank" but with x4 chips it takes both sides and 16 chips to make the ONE, single, rank.

Using a 1GB memory module, the 'High density' memory stick crams the 1GB into ONE RANK by using 16 deeper (twice as deep) x4 bit width chips. And this is how they arrive at the confusing term 'high density'. The chips themselves are no higher in density than the x8 chips but since they are organized as x4 they can cram more 'bytes' into a single rank because 16 chips make up a rank rather than 8, not that it helps make the stick itself any 'higher' in 'density' because you can still only get 16 chips mounted on the thing.

A memory 'slot' is usually designed for 'standard' x8 chips and memory sticks containing 2 ranks. That is how the 'capacity' will be described.
For example, a motherboard that will accept 3GB of memory with 3 slots. Each slot will accept a “double rank” module. Never exceeding 512MB per rank.
Next example, a motherboard that will accept 2GB of memory with 3 slots. This would be tricky and would require reading the owners manual of the system board. Typically on these boards, the first slot will accept a double rank module and the combination of the second and third will accept 2 ranks never exceeding 512MB per rank. I.E.
first slot – double rank module
second slot – single rank
third slot – single rank
or
first slot – double rank
second OR third slot – double rank leaving one of the slots empty.

So, a 1GB 'high density' stick puts 1GB in ONE RANK and a 'standard' (low) density 1GB stick is two 512MB Ranks. Same size, same 'density'. It's the RANK organization that's different.

This still doesn’t mean you cannot use a ‘high density’ module in a motherboard. If the slot will accept a double rank module, never exceeding 512MB per rank, you could still use a 512MB ‘high density’ stick of memory, because it is 512MB in a single rank module.

In conclusion, If you don’t know if your motherboard will accept ‘high density’ modules, buy the more expensive ‘low density’ or what they call ‘100% compatible’ modules. The more money you spent, will give you more assurance and less of a headache later.

zero-one

Hiya - where di find this out?

This is the RAM i bought

I downloaded CPU Z. It's weird. The too old sticks (the ones i bought last month) have valid serial numbers and production dates. The new ones have got FFFFFFFF as the serial number for both and a production time of "Week 165, Year 165".

Is this a problem?

*Upload two pics explaining what i mean.

Attached Images

	old ram.jpg (39.6 KB, 2 views)
	new ram.jpg (39.7 KB, 2 views)

speedster123

http://support.dell.com/support/edoc....htm#wp1059970

Click on "memory"
Are you using matched sets??

damonhill0

Doesn't XP only support 2GB of memory? Are you on 32 bit or 64 bit?