CPU bound
In computer science
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, CPU bound (or compute bound) is when the time for a computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 to complete a task is determined principally by the speed of the central processor
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

: processor utilization is high, perhaps at 100% usage for many seconds or minutes. Interrupt
In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....

s generated by peripheral
A peripheral is a device attached to a host computer, but not part of it, and is more or less dependent on the host. It expands the host's capabilities, but does not form part of the core computer architecture....

s may be processed slowly, or indefinitely delayed.

The concept of CPU bound was developed during early computers, when data paths between computer components were simpler, and it was possible to visually see one component working while another was idle. Example components were CPU, tape drives, hard disks, card-readers, and printers. Computers that predominantly used peripherals were characterized as I/O bound. Establishing that a computer is frequently CPU bound implies that upgrading the CPU or optimizing code will improve the overall computer performance.

With the advent of multiple busses, parallel processing, multiprogramming
Computer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...

, preemptive
Preemption (computing)
In computing, preemption is the act of temporarily interrupting a task being carried out by a computer system, without requiring its cooperation, and with the intention of resuming the task at a later time. Such a change is known as a context switch...

 scheduling, advanced graphics cards, advanced sound cards and generally, more decentralized loads, it became less likely to identify one particular component as always being a bottleneck. It is likely that a computer's bottleneck shifts rapidly between components. Furthermore, in modern computers it is possible to have 100% CPU utilization with minimal impact to another component. Finally, tasks required of modern computers often emphasize quite different components, so that resolving a bottleneck for one task may not affect the performance of another. For these reasons, upgrading a CPU does not always have a dramatic effect. The concept of being CPU bound is now one of many factors considered in modern computer performance.
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