IO bound
Encyclopedia
In computer science
, I/O bound refers to a condition in which the time it takes to complete a computation
is determined principally by the period of time spent waiting for input/output
operations to be completed. This is the opposite of a task being CPU bound
. This circumstance arises when the rate at which data
is requested is slower than the rate it is consumed or, in other words, more time is spent requesting data than processing it.
, which is employed by many computing devices ever conceived, is based on a logically separate central processor unit which requests data from main memory, processes it and writes back the results. Since data must be moved between the CPU and memory along a bus which has a limited data transfer rate, there exists a condition that is known as the Von Neumann bottleneck. Put simply, this means that the data bandwidth
between the CPU and memory tends to limit the overall speed of computation. In terms of the actual technology that makes up a computer, the Von Neumann Bottleneck predicts that it is easier to make the CPU perform calculations faster than it is to supply it with data at the necessary rate for this to be possible.
In recent history, the Von Neumann bottleneck has become more apparent. The design philosophy of modern computers is based upon a physically separate CPU and main memory. It is possible to make the CPU run at a high data transfer rate because data is moved between locations inside them across tiny distances. The physical separation between CPU and main memory, however, requires a data bus to move data across
comparatively long distances of centimetres or more. The problem of making this part of the system operate sufficiently fast to keep up with the CPU has been a great challenge to designers.
must stall its operation while waiting for data to be loaded or unloaded from main memory or secondary storage. With faster computation speed being the primary goal of new computer designs and components such as the CPU and memory being expensive, there is a strong imperative to avoid I/O bound states and eliminating them can yield a more economic improvement in performance than upgrading the CPU or memory.
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...
, I/O bound refers to a condition in which the time it takes to complete a computation
Computation
Computation is defined as any type of calculation. Also defined as use of computer technology in Information processing.Computation is a process following a well-defined model understood and expressed in an algorithm, protocol, network topology, etc...
is determined principally by the period of time spent waiting for input/output
Input/output
In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...
operations to be completed. This is the opposite of a task being CPU bound
CPU bound
In computer science, CPU bound is when the time for a computer to complete a task is determined principally by the speed of the central processor: processor utilization is high, perhaps at 100% usage for many seconds or minutes...
. This circumstance arises when the rate at which data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
is requested is slower than the rate it is consumed or, in other words, more time is spent requesting data than processing it.
I/O bound as an inherent problem in computing
The I/O bound state has been identified as a problem in computing almost since its inception. The Von Neumann architectureVon Neumann architecture
The term Von Neumann architecture, aka the Von Neumann model, derives from a computer architecture proposal by the mathematician and early computer scientist John von Neumann and others, dated June 30, 1945, entitled First Draft of a Report on the EDVAC...
, which is employed by many computing devices ever conceived, is based on a logically separate central processor unit which requests data from main memory, processes it and writes back the results. Since data must be moved between the CPU and memory along a bus which has a limited data transfer rate, there exists a condition that is known as the Von Neumann bottleneck. Put simply, this means that the data bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
between the CPU and memory tends to limit the overall speed of computation. In terms of the actual technology that makes up a computer, the Von Neumann Bottleneck predicts that it is easier to make the CPU perform calculations faster than it is to supply it with data at the necessary rate for this to be possible.
In recent history, the Von Neumann bottleneck has become more apparent. The design philosophy of modern computers is based upon a physically separate CPU and main memory. It is possible to make the CPU run at a high data transfer rate because data is moved between locations inside them across tiny distances. The physical separation between CPU and main memory, however, requires a data bus to move data across
comparatively long distances of centimetres or more. The problem of making this part of the system operate sufficiently fast to keep up with the CPU has been a great challenge to designers.
I/O bound as a practical problem
The I/O bound state is considered undesirable because it means that the CPUCentral 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...
must stall its operation while waiting for data to be loaded or unloaded from main memory or secondary storage. With faster computation speed being the primary goal of new computer designs and components such as the CPU and memory being expensive, there is a strong imperative to avoid I/O bound states and eliminating them can yield a more economic improvement in performance than upgrading the CPU or memory.