A personal computer is designed for use by one person at a time. This is what most of us think about when someone says "computer," because it's the kind of computer we are most likely to see. The computers people use at home or students use in school labs are personal computers.
A laptop is a compact personal computer with all the devices shrunk into one container to make the computer easily portable. The general term device in computer science refers to any hardware component. Thus, a laptop is any computer where all the hardware is inside a single, readily carried container.
A workstation is also a computer designed for use by one person at a time, but it is connected to a network—a set of computers connected together to share data. At an insurance company, for example, all the employees may have computers on their desks with the computers connected to a network so they can share customer data. While computers intended as workstations may be more powerful than personal computers, this is not always the case.
A mainframe is a powerful computer that is shared by multiple users at one time. Each user has a terminal, which in this context is simply a keyboard and screen combination used to access the mainframe. If the terminal is nothing more than a screen and keyboard, it's called a "dumb terminal" because it does no processing of its own. However, a workstation can also be used, in which case it's called a "smart terminal."
A minicomputer is any computer powerful enough to be used by multiple people but not powerful enough to be considered a mainframe. This term is fading from use. A supercomputer is among the fastest of current computers. Because this classification is based on performance, no computer can stay in this category forever. Systems that were considered supercomputers ten years ago are ordinary in their abilities today. A server is a computer on a network that provides a service to other computers. Mainframes are often used as servers, but not every server is a mainframe. Even a personal computer is powerful enough to be a server.
A client is a computer that uses a server for some service. An example of the client-server relationship is an automated teller machine. The ATM is a computer, but all it really knows is how much money it has left inside of it. When you request money from your account at an ATM, the ATM must consult a central computer at your bank to determine if your account has a high enough balance to grant your request and to debit your account once you have been given your money. The ATM is the client in this relationship, and the central computer at the bank is the server.
Binary means having two states. In the computer's case, the two states are off or on. The trick to understanding binary is seeing how a series of these "off" and "on" states can represent any data you can think of. In computer science, the off signals are written as the number 0, and the on signals are written as the number 1. A single on/off indicator, written as a 0 or 1, is called a bit, which comes from the term binary digit.
Bits are formed into bytes, which are groups of eight bits. Why eight? This number of bits allows one byte to store one character, which is any letter, digit, or other symbol that can be displayed by typing on a keyboard. Eight bits allow 256 combinations, which is more than enough for all the lowercase letters (twenty-six), uppercase letters (another twenty-six), digits 0 through 9, and special symbols, like $, %, and the quotation marks.
Even the space between words is a character. When you read that some computer devices can store as much data as a novel or an encyclopedia, that piece of information is relying on the idea of one byte equals one character. If the average word length is five characters (four letters plus the space before the next word) and a typical novel has 80,000 words, then it takes 400,000 bytes to store a novel.
Any data can be stored as binary, as long as every possible value can be matched with a whole number, which can then be turned into a binary value. Data that is already numeric, like students' test grades, inventory counts, or account balances, is easy. Textual data can be stored easily as well, as you've just seen. The process becomes tricky, though, without an obvious one-to-one correspondence between the original data and the set of binary values.
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