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1. Introduction

In this tutorial, we’ll examine two terms commonly used in program development, CPU bound and I/O bound. First, we’ll define them and describe their properties. Then we’ll discuss how to identify them. Finally, we’ll explore the benefits and problems associated with each of them.

2. What Does CPU-Bound Mean?

The term CPU-bound describes a scenario where the execution of a task or program is highly dependent on the CPU. Before we go any further, let’s define what a CPU is. The CPU usually refers to the central processing unit of a computing device, such as a desktop computer. It’s responsible for controlling the execution of tasks and programs in a computer system. As such, a computing device can’t really function without it.

In a CPU-bound environment, most times, the processor is the only component being used for execution. This means that other components in the computer system are rarely used during execution. Due to this dependence, everything concerned with program execution is dependent on the CPU. Consequently, if we want a program to run faster, then we have to increase the speed of the CPU.

Furthermore, CPU-bound operations tend to have few and long CPU bursts. CPU burst refers to the amount of time taken to execute a task, usually with the CPU. As a result, it’s always advisable to assign a lower priority to such tasks to prevent wasting resources:

cpu-bound-timeline

2.1. Examples of Applications

Applications that usually require tons of calculations are a classic example. For instance, High-Performance Computing (HPC) systems can be thought of as CPU-bound. Such systems combine the processing power of several powerful processors in the CPU to deliver higher computing performance.

Due to the speed and efficiency of such systems, they’re capable of computing billions of calculations per second. If we want to increase the performance of the HPC system, in addition to other components, we can increase the processor’s speed. HPC systems have been employed in a number of areas, such as weather prediction, artificial intelligence, and research in general.

In addition to HPC systems, graphics operations are also CPU-bound in the sense that calculations have to be made to render graphics.

2.2. Advantages and Disadvantages

The main advantage is:

  • The use of the CPU results in faster processing of tasks or programs.

The disadvantages are:

  • The use of the processing unit alone results in other system components being idle, hence a waste of resources.
  • Increasing CPU power is an expensive exercise because they’re generally expensive to purchase.

3. What Does I/O Bound Mean?

In contrast, a task or program is I/O bound if its execution is dependent on the input-output system and its resources, such as disk drives and peripheral devices. In I/O bound environments, we wait for resources to be retrieved through the input-output systems. Hence, it’s safe to say that a program or task would execute faster if the input-output system worked faster.

In addition, in executing an I/O bound task, the computing device spends its time performing input-output operations, and other resources, such as the central processing unit, are used less frequently or not at all. The input-output system refers to the input-output component of an operating system. This is usually responsible for the communication or transfer of information between the computing device and the outside.

It should also be noted that I/O bound operations are characterized by many and fewer CPU bursts during execution:

io-bound-timeline

3.1. Examples of Applications

Any application that involves reading and writing data from an input-output system, as well as waiting for information, is considered I/O bound. These include applications like word processing systems, web applications, copying files, and downloading files.

3.2. Advantages and Disadvantages

The main advantage is:

  • Due to the short CPU bursts, they’re usually assigned higher priority during scheduling to ensure that system resources are better used.

The disadvantages are:

  • Programs that are I/O bound are often slower than CPU-bound programs.
  • Due to the use of the input-output system, the time spent waiting for data to be read or written can be substantial. This is considerably slower than the time it takes a processor to complete operations.

4. How to Distinguish the Two?

So how do we decide which category a program or task belongs to? In identifying the category, there are a couple of questions to ask. First, we need to identify which resources make the program or task execute faster. Second, does the program require long CPU bursts or short CPU bursts?

It’s also important to note that some programs or tasks are both CPU and I/O bound. Therefore, we can’t strictly place them into one group.

5. Conclusion

In this article, we defined CPU and I/O bound operations. We discussed some example applications and then listed the pros and cons. Lastly, we outlined how to identify which group an operation or task belongs to.

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