Editing Memory paging (section)

==Performance==
The backing store for a virtual memory operating system is typically many [[order of magnitude|orders of magnitude]] slower than [[random access memory|RAM]]. Additionally, using mechanical storage devices introduces [[access time|delay]], several milliseconds for a hard disk. Therefore, it is desirable to reduce or eliminate swapping, where practical. Some operating systems offer settings to influence the kernel's decisions.
* Linux offers the <code>/proc/sys/vm/[[swappiness]]</code> parameter, which changes the balance between swapping out runtime memory, as opposed to dropping pages from the system [[page cache]].
* Windows 2000, XP, and Vista offer the <code>DisablePagingExecutive</code> registry setting, which controls whether kernel-mode code and data can be eligible for paging out.
* Mainframe computers frequently used head-per-track disk drives or drums for page and swap storage to eliminate seek time, and several technologies<ref>E.g., Rotational Position Sensing on a Block Multiplexor channel</ref> to have multiple concurrent requests to the same device in order to reduce [[rotational latency]].
* Flash memory has a finite number of erase-write cycles (see [[Flash memory#Limitations|limitations of flash memory]]), and the smallest amount of data that can be erased at once might be very large (128 KiB for an Intel X25-M SSD <ref>{{cite web |url=http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size |title=Aligning filesystems to an SSD's erase block size &#124; Thoughts by Ted |publisher=Thunk.org |date=2009-02-20 |access-date=2010-10-28 |url-status=live |archive-url=https://web.archive.org/web/20101113065550/http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size |archive-date=2010-11-13 }}</ref>), seldom coinciding with pagesize. Therefore, flash memory may wear out quickly if used as swap space under tight memory conditions. On the attractive side, flash memory is practically delayless compared to hard disks, and not [[Volatile memory|volatile]] as RAM chips. Schemes like [[ReadyBoost]] and [[Intel Turbo Memory]] are made to exploit these characteristics.

Many [[Unix-like]] operating systems (for example [[AIX]], [[Linux]], and [[Solaris (operating system)|Solaris]]) allow using multiple storage devices for swap space in parallel, to increase performance.

===Swap space size===
In some older virtual memory operating systems, space in swap backing store is reserved when programs allocate memory for runtime data.  Operating system vendors typically issue guidelines about how much swap space should be allocated.