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Re: perche montare 4gb se te ne riconosce 3?
- Scritto da: logicaMente
- Scritto da: chojin

Enable PAE on 32 bit Windows Vista for 4 GB or

More

Memory


http://forums.techarena.in/showthread.php?t=979407

In quell'articolo si legge: " PAE mode is
always enabled by default in Windows Vista as
its required for hardware-based DEP / NX. And
32-bit client versions of Windows Vista (and also
Windows XP) will never support more than a 4GB
address spaces, even with PAE
enabled "Sì, ma i 4GB vengono indirizzati tutti con il PAE.

Re: perche montare 4gb se te ne riconosce 3?
- Scritto da: logicaMente
Scusa, temo di non capire il senso (veramente,
non sono ironico): anche ammesso che sia corretto
ciò che hai scritto, a che serve "indirizzare" la
memoria se poi non è in grado di usare quella
memoria per caricarci
dati/programmi/cache?

Lo chiedo perchè, a parte l'uso di hack più o
meno fantasiosi (che però rischiano magari di far
inca@@are il wGA...) ovunque si trova che gli
windows client (XP e Vista) a 32bit non possono
usare (non vedere, usare) oltre i 3GB, anche in
presenza di main board che ne indirizzerebbero di
più.Vista 32bit indirizza tutti i 4GB con il PAE, sono utilizzabili MA poi dipende dal sistema se una parte di questa memoria non è libera e quindi inutilizzabile. Per questo molti riportano che con 4GB installati possono usare solo da un 2.75GB a 3.5GB o valori simili. --http://topgearelectronics.com/blog/?p=389Answer: Basically youre at the mercy of Microsoft and the chipset. Vista 32-bit will only see 2.75 to 3.5GB. Windows leaves memory mapped I/O and PCI bus reserved addresses mapped to the kernel System Virtual space. Windows can only map 4 Gigabytes worth of pages, so any PCI or I/O space takes away from physical memory pages that it can keep track of. So it shows you the amount of physical memory that it can keep track of and not the amount of physical memory actually present in the hardware.Enabling PAE doesnt allow you to access more memory because Windows still is limited to managing 4 GB of physical address space. Thats because Windows represents physical addresses as 32 bits in the memory management information. Even though the hardware supports more address bits, Windows doesnt use them. The only reason PAE can be enabled on Windows is to provide DEP (Data Execution Prevention) that requires PAE to be enabled.What I said is not completely true of server versions of Windows. Although the kernel doesnt keep track of the extra physical memory in Windows server, an application can use a special set of system calls to map the memory and access it. It doesnt behave like normal, paged virtual memory and cant be used for many of the normal things like file data buffers, etc. Essentially its just a kluge to provide some access to the extra memory.The 32-bit versions of Linux are able to access more than 4 GB of physical address space using PAE.The long answer takes some explanation Heres the official answer from Microsoft:This paper from HP helps explain itthe platform can theoretically support the full 4GB, but your hardware is going to allocate some of the address space (not the physical RAM) to the PCI bus, the video adapter memory address space, and other resources. 32-bit OSs need to use part of the full 4GB address space to address these resources, subtracting from the maximum memory you have available to the OS and applications: The PCI memory addresses starting down from 4 GB are used for things like the BIOS, IO cards, networking, PCI hubs, bus bridges, PCI-Express, and video/graphics cards. The BIOS takes up about 512 KB starting from the very top address. Then each of the other items mentioned are allocated address ranges below the BIOS range. The largest block of addresses is allocated for todays high performance graphics cards which need addresses for at least the amount of memory on the graphics card. The net result is that a high performance x86-based computer may allocate 512 MB to more than 1 GB for the PCI memory address range before any RAM (physical user memory) addresses are allocated.So, if your video adapter has 512MB of RAM (like mine does), your maximum memory is going to at most be 3.5GB, because Vista has to use 512MB of that address space to address your video memory. Itll actually be lower than the 3.5GB because there are other hardware resources that need address space, too. So, it never hurts to fill your computer with 4GB of RAMyoull definitely get the max, but you wont be able to address it all. You probably wont be able to address much more than 3GB, and you might not be able to address more than 2GB.