Editing Computer memory (section)

== Management ==
{{Main|Memory management}}
Proper management of memory is vital for a computer system to operate properly. Modern [[operating system]]s have complex systems to properly manage memory. Failure to do so can lead to bugs or slow performance.

=== Bugs ===
Improper management of memory is a common cause of bugs and security vulnerabilities, including the following types:

* A [[memory leak]] occurs when a program requests memory from the operating system and never returns the memory when it is done with it. A program with this bug will gradually require more and more memory until the program fails as the operating system runs out.
* A [[segmentation fault]] results when a program tries to access memory that it does not have permission to access. Generally, a program doing so will be terminated by the operating system.
* A [[buffer overflow]] occurs when a program writes data to the end of its allocated space and then continues to write data beyond this to memory that has been allocated for other purposes. This may result in erratic program behavior, including memory access errors, incorrect results, a crash, or a breach of system security. They are thus the basis of many software vulnerabilities and can be maliciously exploited.

=== Virtual memory ===
{{Main|Virtual memory}}
Virtual memory is a system where [[physical memory]] is managed by the operating system typically with assistance from a [[memory management unit]], which is part of many modern [[CPU]]s. It allows multiple types of memory to be used. For example, some data can be stored in RAM while other data is stored on a [[hard drive]] (e.g. in a [[swapfile]]), functioning as an extension of the [[cache hierarchy]]. This offers several advantages. Computer programmers no longer need to worry about where their data is physically stored or whether the user's computer will have enough memory. The operating system will place actively used data in RAM, which is much faster than hard disks. When the amount of RAM is not sufficient to run all the current programs, it can result in a situation where the computer spends more time moving data from RAM to disk and back than it does accomplishing tasks; this is known as [[Thrashing (computer science)|thrashing]].

=== Protected memory ===
{{Main|Memory protection}}
Protected memory is a system where each program is given an area of memory to use and is prevented from going outside that range. If the operating system detects that a program has tried to alter memory that does not belong to it, the program is terminated (or otherwise restricted or redirected). This way, only the offending program crashes, and other programs are not affected by the misbehavior (whether accidental or intentional). Use of protected memory greatly enhances both the reliability and security of a computer system.

Without protected memory, it is possible that a bug in one program will alter the memory used by another program. This will cause that other program to run off of corrupted memory with unpredictable results. If the operating system's memory is corrupted, the entire computer system may crash and need to be [[Reboot (computing)|rebooted]]. At times programs intentionally alter the memory used by other programs. This is done by viruses and malware to take over computers. It may also be used benignly by desirable programs which are intended to modify other programs, [[debugger]]s, for example, to insert breakpoints or hooks.