USB is a widely used general-purpose serial interface (汎用シリアルインタフェース) standard for connecting a computer to peripherals by cable.
It uses serial transfer (シリアル転送), sending data one bit at a time over a single signal line. Devices as different as a mouse and an external storage drive connect under the same standard, and a USB hub (USBハブ) lets several devices share one port.
AnalogyIt is like agreeing on a shared language in advance, so people from different places can still talk to each other.
How to rememberShort for Universal Serial Bus: "universal" means it works with anything, and "serial" means data goes out in single file.
Exam points
ExamBus power (バスパワー) is a method in which the computer supplies electricity to a peripheral through the USB cable. Low-power devices can run on it alone, while power-hungry ones use their own supply such as an AC adapter.
ExamHot plugging (ホットプラグ) means connecting or removing a peripheral while the computer stays on, and USB supports it.
ExamUSB connectors come in several shapes, such as Type-A, Type-B and Type-C, which differ by which end they plug into and by size.
Bluetooth is a short-range wireless standard that uses radio waves (電波) to link devices without cables, typically within a few meters up to about 10 m.
It runs on the 2.4 GHz band and draws little power, so it suits small battery-powered gadgets. After an initial pairing (ペアリング) step registers the other device, the two reconnect automatically from then on.
AnalogyThink of a walkie-talkie that only talks to the partners it has been set up with, as long as they are nearby.
How to rememberThe name comes from "Bluetooth", the nickname of Harald I, the 10th-century Danish king who united Denmark and Norway, reflecting the aim of uniting many kinds of devices.
Exam points
ExamBluetooth is a wireless interface (インタフェース) based on radio waves, so a computer and its peripherals connect without any cable.
ExamBluetooth serves to connect gear used close to the main device, such as wireless earphones and keyboards, without wires.
RFID is a technology that reads and writes identification data stored on an IC tag (ICタグ) from a distance, by radio and without contact.
The reader sends out radio waves
A battery-free tag draws power from the waves
The tag sends back its ID data
The tag sends the ID data on its IC chip back by radio, and the reader picks it up.
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An IC tag consists of a tiny IC chip and an antenna, and it answers when it receives radio waves from a reader/writer (リーダライタ). The tag holds data that identifies each individual item, such as a product or a parcel.
AnalogyIt is like a reader calling out by radio to an electronic name badge stuck on a library book and having it answer with its name.
How to rememberShort for Radio Frequency IDentification: you identify (ID) things by radio.
Exam points
ExamA contactless IC card (非接触型ICカード) is an application of RFID: hold the card near a reader and the IC chip inside exchanges data with it by radio.
Mix-upA barcode (バーコード) is a printed pattern read with light, so each one has to be shown to the scanner in turn. RFID communicates by radio, so it can read tags inside a box or many tags in one pass.
NFC is a short-range wireless communication (近距離無線通信) standard in which devices talk by radio once they come within about 10 cm, and it is a type of RFID.
Communication starts as soon as a card or smartphone is held up (かざす) to a reader, and the short range makes an unintended connection unlikely. Besides reading and writing cards, it also lets two smartphones swap data.
AnalogyIt is like someone you can only hear once you are close enough to shake hands.
How to rememberShort for Near Field Communication: communicating in the "near field", right next to the device.
Exam points
ExamAmong short-range wireless methods, NFC has an especially short range. Bringing a device up to its partner is therefore itself the signal that starts communication.
ExamTapping an IC transit card (IC乗車券) at a station's automatic ticket gate is a typical use of communication that follows the NFC standard.
Mix-upRFID covers the whole family of technologies that read and write IC tags (ICタグ) by radio, with ranges from a few centimeters to a few meters depending on the method. NFC is the international standard within it that is limited to proximity communication of about 10 cm.
IrDA is a wireless standard in which devices send and receive data over infrared light (赤外線) at short range, about 1 m.
Infrared is a form of light that travels in straight lines, so the transmitter and receiver must face each other with nothing in between. It was once used to exchange data between laptops and handheld information devices.
AnalogyLike a TV remote, it is a light signal that does not get through unless you point it the right way.
How to rememberShort for Infrared Data Association, the body that set the standard, whose name became the standard's name. "Ir" stands for infrared.
Exam points
ExamIrDA is a wireless standard that uses infrared (赤外線) as its medium, so devices communicate without being connected by cable.
Mix-upBluetooth and IrDA are both cable-free short-range wireless methods, but they differ in that Bluetooth uses radio waves and IrDA uses infrared.