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[LÖST] Minnesproblem i Windows XP Professional, 3GB RAM max?


mimar
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Hej!

Har hittat ett litet problem när man trycker i mer minne än 3GB i Windows XP Professional.

Själv köpte jag till 4GB DDR2 till min nya stationära dator. Till min häpnad så visade endast operativsystem 3GB. Trots att allt minne visas i Bios samt uppstarten. Vad jag har googlat mig fram till så ska man kunna fixa till detta problem genom att ta bort minnesväxlingsfilen samt möjliggöra PAE funktionen i boot.ini.

Är det någon som har någon kännedom kring växeln man ska lägga till samt var den ska läggas in?

Vore tacksam för svar!

/Micke

Ämnet redigerat av stenis, har förtydligat ämnet/rubriken

Ämnet löst och låst av stenis, för vidare frgåor starta en ny tråd

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Har hittat ett litet problem när man trycker i mer minne än 3GB i Windows XP Professional.

Själv köpte jag till 4GB DDR2 till min nya stationära dator. Till min häpnad så visade endast operativsystem 3GB. Trots att allt minne visas i Bios samt uppstarten.

Enda möjligheten till mer än 3BG i Windows, är att du kör med 64-bitars operativ.

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Ja, ett 'vanligt' 32-bitars Windows reserverar adressområdet mellan 3GB och 4GB för hårdvaru-

och system adresseringar. Skall du använda hela ditt inmonterade minne så måste du uppgradera

till Windows XP pro. x64 som idag hanterar minst 32GB (Teoretiskt upp till 16TB).

Om du söker här i forumet så hittar du mängder av inlägg i denna frågan.

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det var inte bra gjort av MS tänka sig att man måste byta sig till x64 för att ha mer än 3 GB minne

När MS konstruerade XP så fanns det nog ingen som trodde att man skulle köra med

dagens "groteska" storlek på RAM

Vista är man ju tvungen att ändra på i SP1 eftersom företag vägrar uppgradera sina burkar

till kanske mer än 2 GB RAM

Jag har fortanade inte sett värden på minnesanvändning i Vista dvs hur det ser ut med senaste spel  ???

Tungt lastade servrar behöver 4GB minne.... :D

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kanske de ordnar det när sp3 kommer

Nej, detta är en grundläggande funktionalitet i Windows 32-bitars operstivsystem.

Det är inget man kan förändra i efterhand.

Bland annat för att alla 32-bits drivrutiner är anpassade till detta adressområde.

Detta är en av anledningarna till att 64-bits drivrutiner krävs i x64 Windows.

En Service Pack installation kan aldrig förändra grundläggande konstruktioner, endast bygga på nya funktioner.

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För lite mer information i detta ämne.Klippt från itproffs.se[/size][/size]

Vänligen

Åke

quote:

ORIGINAL = TabBlogger

The 3GB-not-4GB RAM problem

Problem statement:

I just bought a system with 4GB of physical RAM in it. The BIOS posts 4GB, but Windows tells me that I have anywhere from 2.75 - 3.5GB of RAM. Where is the rest of my RAM?

Summary:

If you are running 32-bit Windows, you must live with it. You will not ever see all 4GB of RAM you've paid for.

If you are running 64-bit Windows, you may have to live with it. Depending on your motherboard's chipset, your system may support memory remapping. If so, you will be able to use all 4GB of RAM.

Detailed:

Due to an architectural decision made long ago, if you have 4GB of physical RAM installed, Windows is only able to report a portion of the physical 4GB of RAM (ranges from ~2.75GB to 3.5GB depending on the devices installed, motherboard's chipset & BIOS).

This behavior is due to "memory mapped IO reservations". Those reservations overlay the physical address space and mask out those physical addresses so that they cannot be used for working memory. This is independent of the OS running on the machine.

Significant chunks of address space below 4GB (the highest address accessible via 32-bit) get reserved for use by system hardware:

BIOS including ACPI and legacy video support

PCI bus including bridges etc.

PCI Express support will reserve at least 256MB, up to 768MB depending on graphics card installed memory

What this means is a typical system may see between ~256MB and 1GB of address space below 4GB reserved for hardware use that the OS cannot access. Intel chipset specs are pretty good at explaining what address ranges gets reserved by default and in some cases call out that 1.5GB is always reserved and thus inaccessible to Windows.

When looking at memory in systems (be it desktop or notebook) there are three questions to ask that will tell you the maximum amount of memory your O/S will be able to use:

1. What O/S Edition have you installed?

a. 32-bit Windows is limited to a maximum of 4GB and cannot see any pages above 4GB.

b. 64-bit Windows can use between 8GB and 128GB depending on SKU.

2. What address range can your processor actually access?

a. Typically thatll be 40-bit addressing today for x64 (Intel EM64T/AMD64), but older processors may be limited to 36-bit or even 32-bit

3. Can your systems chipset map memory above 4GB?

a. Mobile chipsets on sale today cannot (but that may change with time)

b. Newer workstations (which use chipsets developed for single or multi-proc servers) usually can.

Windows can remap memory from below 4GB to above 4GB and use it there, however, that relies on the three points above:

1. Can Windows access memory above 4GB?

a. 32-bit NO

b. 64-bit Maybe (due to chipset limitations)

2. Can your processor access memory above 4GB?

a. If its recent then it might, and if its either AMD64 or EM64T its almost certain

3. Does your chipset allow pages to be remapped above 4GB?

a. Probably not and thats whats catching people who install 64-bit Vista to work around point 1 they find they still cannot see above 4GB

In some cases, OEMs may be able to tweak their BIOS to reserve less memory for platform use, but were not talking a huge difference (ie, 100s of MBs).

In the end a 32-bit OS and/or application can only, ever, handle 4GB of memory at a time, the AWE stuff just swaps chunks of memory in and out of that 4GB space, thus fooling the application and OS into using more space than it can see.

Physical Address Extension (PAE), extends the physical address space to 36-bits if your HW supports this. For most operations, the processor execution units will only see 32-bit addresses, the MMU will take care of the translation to 36bit addresses. No swapping here, only page translations (which are used regardless of PAE being on or not), this is a fundamental feature of any virtual memory operating system.

The OS and apps only see 32-bit addresses because the registers are limited to 32-bits (hence the 32-bit architecture nomenclature). These are linear addresses which are extended to 36-bits in the translation to physical addresses, but they never show up in registers since theres no room. Its all internal until the address lines coming out of the chip are toggled. Thus my comment above about if your H/W supports this (PAE)". Im not going into how that works

So, the OS can happily handle up to 64 GB of memory for 32-bit PAE-able systems.

Hope this helps explain the whole, Why cant I see 4 Gig of RAM in my system? thing

BTW This does not change for Vista either

references:

http://support.microsoft.com/kb/929605/en-us

HWJunkie DL (MSFT internal)

Bob Heath (original author of this summary material)

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