Windows 7 32 bit Ultimate showing 3.24 GB Usable Memory

According to Microsoft's own knowledge base article 929605, all 32-bit versions of Vista support up to 4GB of memory, but the actual usable address space will be less than 4GB. The reason for this is that a section of the memory is set aside for memory map interfaces. This is generally a space that is set aside to ensure driver compatibility and the amount used will vary depending upon the devices installed in the system. Typically, a system with 4GB of RAM will report only 3.5GB of addressable space.

If a computer has many installed devices, the available memory may be reduced to 3 GB or less. However, the maximum memory available in 32-bit versions of Windows Vista is typically 3.12 GB.

This same limitation apllies to Windows 7 32 bit

But this is not the case for the 64-bit flavor of Windows 7. The Home Basic and Starter SKUs can manage up to 8 GB of RAM, with Home Premium taking the limit to 16 GB. The Professional, Enterprise and Ultimate versions of Windows 7 will support as much as 192 GB of RAM.

• A 32-bit OS can only address about 3 GB of memory. You need to install a 64-bit OS if you have 4 GB or more of memory! 
• You can use 64-bit OS with less than 4 GB of memory, just need to make sure your processor is 64-bit compatible. You need to get 64-bit Windows
• There are some hacks that claim to make 32-bit windows use more than 4GB RAM. I have never used them but you might want to take a look if you don't wish to use 64-bit OS yet.
• Technically, a computer supporting hardware-enabled Data Execution Prevention (DEP) can use more than 4 GB by utilizing the 36-bit physical addressing mode (PAE) while running a 32-bit OS.
• The type of processor needed to support the Physical Address Extension. ("a computer supporting hardware-enabled DEP")
  Using the PAE mode kernel on systems running 32-bit version OS requires a processor with an architecture that supports hardware-enforced DEP such as the Intel Pentium Pro or later.
  
  You are referring to the unrelated software-enforced DEP which is a memory protection feature that is built into the Windows OS.
  
  In addition, it is only "flaky and unworkable" if one doesn't make sure that the drivers and devices are not set to be compatible; which I pointed out, as well as added that it is far more advisable to simply use a 64-bit OS.
  
  Furthermore, all of this was in response to the following quote to show that it is possible (although not viable) that a 32-bit OS can break the infamous folly of the 4GB memory limit.
  
  "A 32-bit OS can only address about 3 GB of memory. You need to install a 64-bit OS if you have 4 GB or more of memory!"

Windows 7 32 bit Ultimate showing 3.24 GB Usable Memory