Windows System Overview

1.4GT Tuning

StackOverflow has a question about 4GT: http://stackoverflow.com/questions/2883206/ maximum-size-of-application-memory-space-on-32-x86-2-gb-or-1-gb/2883252#2883252

Q: 32-bit systems, how much memory can an application theoretically use?

Answer: specific to the operating system.

The 32-bit Windows system assigns 2GB to the application by default, 2GB to the kernel, so your program can theoretically allocate 2GB. You can modify this value by using the 4GT boot flag. This MSDN article describes these.

64-bit Windows systems can use more, such as 8TB.

2.PAE (physical Address Extension)

--Physical Address extension. Ask questions here, what does PAE do?

PAE is a feature of the x86 processor that allows IA-32 processor-based systems to access more than 4GB of memory. If you have 16GB of RAM on a 32-bit machine, if there is no PAE, all applications plus the kernel can use only 4GB of memory. But if PAE is turned on, each process will have its own 32-bit address space, so you can use all 16GB of RAM. It's just not for a process.

For applications that require more than 4GB of memory, in addition to the general PAE support, the operating system is required to provide additional special technology. On Windows, this technology is called Address Windowing Extensions (AWE). On Unix-like systems, there are a number of techniques in use, such as using mmap () to map a subset of files to the address space as needed, but this has not yet become a standard.