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Vista & 4Gb ram?


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Satt och pulade med min nya Vistaburk när jag upptäckte nåt (enligt mig) mycket märkligt!

Överallt där internminnet visas så står det 3Gb eller 3069 Mb eller liknande. Men datorn ska innehålla 4Gb ram och det går inte för allt i världen att se!

Kontaktade Dell supporten (XPS-varianten) och frågade om det var nåt fel.

Detta är svaret jag fick!

Ursäktar redan nu för ett långt svar, men jag tror att det kan vara matnyttigt för gänget här på forumet!

Hoppas det iallafall! ;D

Hello Mr Tinglof

Here is the information about the 4GB issue on Vista

1)        Summary on Windows Memory Limitation:

Windows was updated some years ago to reserve a certain amount of memory

when it has the luxury of 4 gigs of memory to work with: according to

Microsoft, this was done to make compatibility for hardware drivers

easier (these drivers are what makes the computer and windows work with

items like graphics or sound card and some other internal hardware).

Windows then reports it to you as if the memory it reserved just isn't

there. If there was nothing else there outside window to reserve memory,

windows would tell you that you have slightly above 3 gig available.

If windows doesn't have these 4 gigs to play with, it doesn't reserve

the memory at all, reports it correctly and just uses memory as it needs


What is happening at the same time though, is that your graphics card is

also reserving memory. The graphics card needs this memory all the time,

and this happens outside of the 4 gig issue.

So when you have 4 gigs in, windows takes nearly 1 gig in reserve, and

the graphics card takes slightly more than a half a gig, leaving you

with around 2.5 gigs.

None of this happens at 2 gig or below, as the graphics card does have

its own limited memory.

Microsoft do recognise this but there are no fixes for Windows XP, as

these changes to Windows were made before 4 gigs of ram in a system was

commonplace or even expected.

There is a fix for Vista listed below.





2)        Memory Limitation Detail :

On a system configured with 4 GB of random-access memory (RAM),

Microsoft® Windows® reports 3.0 to 3.8 GB of available memory. The

same behavior is seen in Linux and other operating systems, as this is a

limitation of 32-bit addressing used in IA-32 systems.

<<Picture (Device Independent Bitmap)>>        NOTE:        At this time,

Dell portable systems reserve 1 GB of memory for input/output (I/O)

space in the basic input/output system (BIOS), making the total memory

available 3,000 MB, which equals 3 GB. This is set in the BIOS and

cannot be changed by the user.       

This is a limitation of a 32-bit architecture. The system can only

address 4 GB of allocated memory. Allocated memory is made up of

physical RAM, and any I/O space needed by devices. The way memory is

allocated is that starting at 4 GB, the system allocates device I/O

addresses working its way down. Normally this is not a problem, but when

systems have 4 GB of physical memory, the addresses needed to address

RAM overlap the space needed for I/O. In this case, the need for I/O

space takes precedence, and the amount of RAM visible to the operating

system and applications is limited to 4 GB minus I/O space. Examples of

devices that consume I/O space are:

*        System BIOS

*        PCI Express configuration space and memory for PCI Express


*        Memory mappy I/O

*        Motherboard Resources (I/OxAPIC)

*        Chipset

*        PCI Enumeration

For example: If you have 4GB of system memory, an Intel 915g Express

chipset, Windows XP with Service Pack 2, and a PCI Express graphics card

the remaining system memory as reported by System Information would be

~3.25GB. The same configuration but with 2GB of system memory would

result in all 2GB being available. This is due to the limited capability

of memory mapping (or limited amount of addresses) on 32-bit

architecture systems.

<<Picture (Device Independent Bitmap)>>        NOTE:        Server systems

are able to extend the address space with physical address extension

(PAE) . This option is not available on desktop and workstation systems.

3)        Fix for Vista Below:

Enable support for 4GB of RAM (or more) in Vista 32-bit

On a computer that has 4 GB of RAM, the System Properties dialog box and

the System Information dialog box may report less memory than you

expect. This problem occurs because the address space is limited to 4 GB

in a 32-bit hardware environment. Memory may be relocated to make room

for addresses that the basic input/output system (BIOS) reserves for

hardware. However, because of this limitation, Windows Vista cannot

access memory that is relocated above the 4 GB boundary.

Solution: Open an elevated Command Prompt, type BCDEdit /set pae

ForceEnable and press Enter.

The pae parameter enables Physical Address Extension (PAE). On 32-bit

versions of Windows, PAE is disabled by default. PAE is an addressing

strategy that uses a page-translation hierarchy to enable systems with

32-bit addressing to address more than 4 GB of physical memory. PAE also

supports several advanced system and processor features, such as Data

Execution Prevention (DEP; "No execute"), Non-Uniform Memory

Architecture (NUMA), and hot-add memory, so it is also used on computers

with less than 4 GB of memory. PAE must be supported by the processor.

On a computer that supports hardware-enabled Data Execution Prevention

(DEP), PAE is automatically enabled when DEP is enabled and

automatically disabled when you disable DEP. To enable PAE when DEP is

disabled, you must enable PAE explicitly: Open an elevated Command


Type BCDEdit /set nx AlwaysOff & BCDEdit /set pae ForceEnable and press




Karl Payne

XPS Support Specialist

Där ser man!

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