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Memory management is confusing, perhaps more so than any other aspect of PC performance. If you scour the Web for information on this topic, you will surely run into misguided advice and technical errors. Knowing the meaning of the following specialized memory-measurement terms helps you make sense of it all:
Physical memory refers to actual RAM chips or modules, typically installed on a computer’s motherboard. The amount of physical RAM available to Windows might be less than the total physical amount if another system component is using that memory for its own purposes, as is the case with “shared memory” video subsystems on portable computers. Physical memory measurements (total and in use) are reported on the Performance tab of Windows Task Manager and on the Memory tab of Resource Monitor.
Virtual memory consists of physical memory plus the amount of space in the page file, which is stored on the hard disk.
Kernel memory is owned by Windows and is used to provide system services to applications. Paged memory can be backed up to the page file and replaced by application memory if necessary. Nonpaged memory must remain in physical RAM at all times.
Cached memory holds data or program code that has been fetched into memory during the current session but is no longer in use now. If necessary, the Windows memory manager will flush the contents of cached memory to make room for newly summoned data.
Free memory represents RAM that does not contain any data or program code and is free for use immediately.
Working Set is the term that defines the amount of memory currently in use for a process. Private Working Set is the amount of memory that is dedicated to that process and will not be given up for other programs to use; Shareable Working Set can be surrendered if physical RAM begins to run scarce. Peak Working Set is the highest value recorded for the current instance of this process.
Commit Charge (also called commit size) is the total amount of virtual memory that a program has touched (committed) in the current session, including memory that has been paged out of physical memory to the disk-backed page file. The Memory and Physical Memory counters on Task Manager’s Performance tab represent the sum of this value for all processes and the kernel. The Commit Charge Limit is the total amount of physical RAM and page file available—in other words, the maximum virtual memory.
Hard faults are also known as page faults. Despite the negative connotation of the name, this is not an error condition. Rather, it represents an instance where a block of memory needed by the operating system or an application has to be fetched from the page file on the hard disk instead of from physical memory. A consistently high number of hard faults per second indicates a large—perhaps excessive—reliance on virtual memory, with consequent adverse performance effects.
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