As you may know the 32 bit, also called x86, editions of Windows Vista cannot address more than 4 GB of memory. You may think this 4 GB is a limit of the processor but this isn’t true; using Physical Address Extension (PAE) it’s possible to address more memory

Enterprise Server versions of Windows (2003 and 2008) can already address more than 4 GB of memory so why can we not do that with Vista? The answer is: Microsoft doesn’t want that! It is all just a licensing matter, we can see this in the registry. Take RegEdit and goto HKLM\CurrentControlSet\Control\ProductOptions and doubleclick the Value ProductPolicy, scroll down a little until you see the value “Kernel-PhysicalMemoryAllowedx86”, next to it is the value 01 00 which corresponds to 4096 (1000 is the Hex of 4096):


We can also see where this (and other licensing values) come from: if we look in %systemroot%\system32\licensing\ppdlic al license values are in XML files. The memory value is in Kernel-ppdlic.xrm-ms:


We cannot make alterations to the registry values or to this xml file; the registry values are rebuild on every reboot and the xml file is protected with a signature

Unlike other licensing values (like activation) which are checked through slc.dll this particular value is checked and enforced in the Kernel. I though that patching the kernel was not possible due to Vista’s integrity checks. But then I read Geoff Chappell’s article about Vista’s Memory Limit. Geoff describes in detail how and where the check is done and even shows us what to patch.

I followed Geoff’s description and patched my kernel (carefully read Geoff’s instruction about checksum, signing and so on!) and I can confirm that his patch works perfectly!

I also noticed something else: my Dell Laptop has 4 GB of memory of which I was only able to use about 3,5 GB. This is due to a portion of the address space that is allocated to my video card (address space, not memory!). We can see with Alex Ionescu’s MemInfo tool there’s a gap between 9F0000 and 100000:


We can also see in TaskManager that only 3581 MB is available:


Let’s see what that looks like after the patch:


We gained the missing memory 😉

TaskManager confirms that:


If you would like to patch your kernel you can download the dUP2 file below. Please check if creating and/or using this patch is legal according to your country’s laws and your license agreement and of course carefully read Geoff’s instructions.

The patch was tested on both SP1 and SP2.

Vista NT Kernel Patch (11768 downloads)