Question : Problem: Page Pool

Whats the "Page Pool" on physical memory?  How does it relate to the system file cache?  (Or are they related at all?)

Answer : Problem: Page Pool

What is Virtual Memory?
A program instruction on an Intel 386 or later CPU can address up to 4GB of memory, using its full 32 bits. This is normally far more than the RAM of the machine. (The 32nd exponent of 2 is exactly 4,294,967,296, or 4 GB. 32 binary digits allow the representation of 4,294,967,296 numbers  counting 0.) So the hardware provides for programs to operate in terms of as much as they wish of this full 4GB space as Virtual Memory, those parts of the program and data which are currently active being loaded into Physical Random Access Memory (RAM). The processor itself then translates (maps) the virtual addresses from an instruction into the correct physical equivalents, doing this on the fly as the instruction is executed. The processor manages the mapping in terms of pages of 4 Kilobytes each - a size that has implications for managing virtual memory by the system.



What are Page Faults?
Only those parts of the program and data that are currently in active use need to be held in physical RAM. Other parts are then held in a swap file (as its called in Windows 95/98/ME: Win386.swp) or page file (in Windows NT versions including Windows 2000 and XP: pagefile.sys). When a program tries to access some address that is not currently in physical RAM, it generates an interrupt, called a Page Fault. This asks the system to retrieve the 4 KB page containing the address from the page file (or in the case of code possibly from the original program file). This  a valid page fault  normally happens quite invisibly. Sometimes, through program or hardware error, the page is not there either. The system then has an Invalid Page Fault error. This will be a fatal error if detected in a program: if it is seen within the system itself (perhaps because a program sent it a bad request to do something), it may manifest itself as a blue screen failure with a STOP code: consult the page on STOP Messages on this site.

If there is pressure on space in RAM, then parts of code and data that are not currently needed can be paged out in order to make room  the page file can thus be seen as an overflow area to make the RAM behave as if it were larger than it is.


In most Windows OS cases and what is loaded into RAM:


Items in RAM can be divided into:

1)The Non-Paged area. Parts of the System which are so important that they may never be paged out - the area of RAM used for these is called in XP the Non-Paged area. Because this mainly contains core code of the system, which is not likely to contain serious faults, a Blue Screen referring to Page Fault in Non-Paged area probably indicates a serious hardware problem with the RAM modules, or possibly damaged code resulting from a defective Hard disk. It is, though, possible that external utility software (e.g. Norton) may put modules there too, so if such faults arise when you have recently installed or updated something of this sort, try uninstalling it.

2)The Page Pool which can be used to hold:
Program code,
Data pages that have had actual data written to them, and
A basic amount of space for the file cache (known in Windows 9x systems as Vcache) of files that have recently been read from or written to hard disk.
Any remaining RAM will be used to make the file cache larger.

Hope this helps.....