View source for System resource

{{Short description|Any component of a computer system with limited availability, physical or virtual}}
{{distinguish|Computational resource}}{{other uses|Resource (disambiguation)}}

A [[Computer|computer]] '''system resource''' is any [[Computer hardware|hardware]] or [[Software|software]] aspect of limited availability that is accessible to a [[Computer|computer]] system. Like any [[Earth:Resource|resource]], computer system resources can be exhausted, and issues arise due to [[Finance:Scarcity|scarcity]].

[[Resource management (computing)|Resource management]], a key aspect of [[Design|design]]ing hardware and [[Software design|software]], includes preventing [[Resource leak|resource leak]]s (not releasing a resource done with it) and handling [[Resource contention|resource contention]] (when multiple processes want to access the same resource). Computing resources are used in [[Cloud computing|cloud computing]] to provide services through networks.

==Fragmentation==
A linearly addressable resource, such as memory and storage, can be used for an allocation that is either ''contiguous'' or ''non-contiguous''. For example, dynamic memory is generally allocated as a contiguous block that consists of a portion of memory from a starting address and running for a certain length. On the other hand, storage space is typically allocated by a [[File system|file system]] as non-contiguous blocks throughout the storage device even though consumers of a file can treat it as a linear sequence; logically contiguous. The resource has an overall capacity as well as the capacity to support an allocation of a certain size. For example, RAM might have enough free space to support allocating 1024 1MB blocks although not enough contiguous free space to support allocating a single 1GB block even though the sum of the smaller blocks equals the size of the large block. [[Fragmentation (computing)|Fragmentation]] describes the amount to which linear resources are stored non-contiguously, and a highly fragmented resource may degrade performance.

==Compression==
One can also distinguish ''compressible'' from ''incompressible'' resources.<ref>[https://github.com/kubernetes/kubernetes/blob/release-1.5/docs/design/resources.md The Kubernetes resource model]: "Some resources, such as CPU and network bandwidth, are compressible, meaning that their usage can potentially be throttled in a relatively benign manner."</ref> Compressible resources, such as CPU and network bandwidth, can be throttled benignly. The user will be slowed proportionally to the throttling, but will otherwise proceed normally. Other resources, such as memory, cannot be throttled without either causing failure (inability to allocate memory typically causes failure) or performance degradation, such as due to [[Thrashing (computer science)|thrashing]] (paging slows processing throughput). The distinction is not always clear. For example, a paging system can allow main memory (primary storage) to be compressed (by paging to secondary storage), and some systems allow discardable memory for caches, which is compressible without disastrous performance impact. 

Electrical power may be compressible. Without sufficient power an electrical device cannot run, and will stop or crash. But, some devices, such as mobile phones, support degraded operation at reduced power. Some devices allow for suspending operations (without loss of data) until power is restored.

==Examples==

The types of resources and issues that arise due to their scarcity is vast. 

For example, [[Computer memory|memory]] is a resource since a computer has a fixed amount. For many applications, the amount is so large compared to its needs that the resource is essentially unlimited. But, if many application with modest requirements are running concurrently, or if an application does require large amounts of memory, then [[Runtime (program lifecycle phase)|runtime]] issues occur as the amount of free memory approaches zero. Applications are no longer able to allocate memory and will probably fail.

Another well-known resource is the processor. It differs from memory in that it is not reserved. Nonetheless, as the processor becomes more loaded with work, the time waiting for the processor increases, and processing throughput degrades. This often leads to inferior [[User experience|user experience]] or in a time-critical application, loss of critical system functionality.

Resources can be layered and intertwined. For example, a [[Computer file|file]] is a resource since each file is unique. A file consumes storage space which has a fixed size. When a file is opened, generally memory is allocated for the purpose of accessing the file. This file object is both a unique resource and consumes memory (a resource). 

Some resources are accessed via a [[Handle (computing)|handle]] such as a [[Lookup table|lookup table]] key or [[Pointer (computer programming)|pointer]]. Although the handle my consume memory, the handle itself is not considered a resource since it can be duplicated at little cost.

On the boot process of the modern operating systems, the [[ACPI]] protocol<ref>https://maplecircuit.dev/std/acpi.html</ref> or the [[Devicetree]] protocol<ref>https://www.kernel.org/doc/html/latest/devicetree/usage-model.html</ref> is often used to deliver hardware resources information.

Notable resources include:

* Cache space, including [[CPU cache]] and MMU cache ([[Translation lookaside buffer|translation lookaside buffer]])
* [[Central processing unit|CPU]], both time on a single CPU and use of multiple CPUs – see [[Computer multitasking|multitasking]]
* [[Direct memory access]] (DMA) channels
* [[Power management|Electrical power]]
* Input/output throughput
* [[Interrupt request (PC architecture)|Interrupt request]] lines
* [[Lock (computer science)|Locks]]
* [[Computer memory|Memory]]; including [[Random-access memory|physical RAM]] and [[Virtual memory|virtual memory]] – see [[Memory management|memory management]]
* Memory-mapped I/O
* Network throughput
* [[Object (computer science)|Objects]], such as memory managed in native code, from Java; or objects in the [[Document Object Model]] (DOM), from [[JavaScript]]
* [[Engineering:Peripheral|Peripheral]]s
* Port-mapped I/O
* [[Randomness]]
* Storage, including overall space as well as contiguous space

== See also ==
* {{Annotated link|Computational resource}}
* {{Annotated link|Linear scheduling method}}
* {{Annotated link|Sequence step algorithm}}
* {{Annotated link|System monitor}}

== References ==
{{reflist}}

[[Category:Computing terminology]]

{{Sourceattribution|System resource}}