3.6Hardware

The mechanisms covered so far—the CPU, main memory, the OS—ultimately run on physical, visible hardware. This section covers a wide range of hardware, from familiar devices like PCs to small computers embedded inside home appliances and IoT devices that sense their surroundings, along with the basics of the storage and input/output devices that support them.

3.6.1Types of computers and I/O devices

• A server is a dedicated computer that provides services to other computers (clients). An embedded system is a computer built into a device like a home appliance or a car, specialized for one specific function and usually unnoticed. Depending on purpose, computers come in many forms—desktops, laptops, servers, embedded devices, and more.
• An input device brings information into a computer (keyboard, mouse, scanner, microphone, etc.). An output device turns processing results into a form people can perceive (display, printer, speaker, etc.). Devices such as touch panels serve both roles as input/output devices.

3.6.2Storage devices, electrical circuits, IoT devices, and power saving

• HDD (hard disk drive) reads and writes data magnetically by spinning a magnetic disk. It offers large capacity at a relatively low cost, but its moving parts make it slower and more shock-sensitive than an SSD. SSD (solid state drive) stores data in semiconductor memory. With no moving parts, it is faster, lighter, and more shock-resistant than an HDD, though generally more expensive per unit of capacity.
• Electrical/electronic circuit basics: relationships among quantities such as current, voltage, and resistance (Ohm's law: voltage = current x resistance), and the distinction between conductors (which carry current) and insulators (which do not)—basic physical laws underlying how hardware works.
• An IoT (Internet of Things) device is a general term for internet-connected "things." A sensor detects and digitizes conditions in the environment, such as temperature, light, or motion. An actuator physically acts on the world—such as driving a motor—in response to a received instruction. Pairing sensors with actuators is what lets an IoT device "sense and act."
• Power saving refers to measures that reduce a device's power consumption—for example, automatically entering sleep mode during idle periods. It helps extend battery life and reduce environmental impact.

Consider a smart air conditioner to see how these hardware elements connect. Inside it is an embedded system—a small computer specialized for one specific function. Unlike a general-purpose PC, it lacks broad flexibility, but reliably handles its limited job of temperature control. A built-in sensor detects the room temperature and turns it into data, which travels over the home network to a server on the internet (or a cloud service). When a user sets the target temperature to 24 degrees via a smartphone app, that instruction travels through the server back to the air conditioner, where an actuator (the motor or compressor drive) physically adjusts airflow and cooling strength. This chain—sensing with a sensor and acting with an actuator—is what makes the air conditioner an IoT device. To keep a long-term record of operation history and settings, it is common to store the data on the server side using a fast, shock-resistant SSD rather than an HDD with its moving parts (HDDs suit applications wanting large capacity cheaply, while SSDs suit applications prioritizing speed and durability). The air conditioner itself is also designed to automatically switch into a power-saving mode when no one is in the room, controlled to run on the minimum power necessary based on basic electrical/electronic circuit properties like current, voltage, and resistance. What the user enters via the remote control (an input device) is shown on the unit's display (an output device) as the current set temperature, so a person can confirm the result.

3.6.3Section summary

• Servers provide services; embedded systems are small computers specialized for one function
• HDD = spinning magnetic disk (large capacity, cheap); SSD = semiconductor memory (fast, light, shock-resistant)
• IoT devices combine a sensor (sensing) and an actuator (acting physically). Power saving reduces consumption