Physical Memory:
Physical memory refers to actual RAM chips or modules, typically installed on a computer’s
motherboard.
Hardware Reserved (296 MB) is the memory space reserved by hardware drivers which must be
always remain on the RAM. This memory is essentially locked and is not available to the memory
manager. A major part of this is the dedicated Graphics Memory reserved through BIOS.
In Use (1648 MB) memory is the sum total of Working Sets of all running processes owned by the
operating system, kernel (non-paged pool), drivers and the various applications.
Modified (52 MB) memory contains modified pages that have been removed from process working
sets, because it was idle for long. Modified memory contents must be written to disk before it can
be repurposed. As such it is currently not in use but can still be quickly pulled into service if
needed. If memory demand runs high or the modified list have grown beyond a certain threshold,
the memory manager arranges to write pages from the modified memory to the page file on hard
disc, and moves those pages from the Modified to the Free memory.
Standby (1111 MB): When a process exits normally, the memory manager moves the unmodified
pages in the working set to the Standby memory, which effectively makes the Standby memory a
true cache of recently used files. By keeping these pages on the Standby list, the memory manager
reduces the need to re-fetch the information from web/disk/network location which is more
involved and time consuming, should the pages be required again.
When a process requests for a page, the memory manager first looks for the page in the Standby
memory and if available, returns it as a working set. This is called repurposing a page. If the page is
not present in Standby, the memory manager loads it from the Hard Disk into the Free Memory
which then becomes part of the process working set.
All pages on the Standby list are available for memory allocation requests. The memory pages in
Standby list are prioritized in a range of 0-7, with 7 being the highest. When a process requests
additional memory and there is not enough memory in the Free list, the memory manager takes a
page with low priority from the Standby list, and releases it to the Free list for the new process to
occupy.
The Free (989 MB) memory are the locations that have not yet been allocated to any process OR
were previously allocated but returned to the memory manager for reuse when the process ended.
All memory demand by the system is met from the Free memory.
The memory manager maintains a thread that wakes up periodically to initialize pages on the Free
page list so that it can move them to the Zero page list. The Zero page list contains pages that have
been initialized to zero, ready for use when the memory manager needs a new page.
Installed Physical Memory is the RAM installed = 4GB = 4096 MB.
Installed Memory = In Use + Modified + Standby + Free + Hardware Reserved
= 1648 + 52 + 1111 + 989 + 296 = 4096 MB.
If installed RAM is sufficiently greater than the Committed (peak value over time), then the system
is unlikely to experience any memory constraint.