The system unit
A system unit houses the processor and the memory of a personal computer system. If you were to remove the cover of the system unit and look inside, you would see the parts that make up a system unit. Although it is not necessary to know how each of these parts works, it is useful, from a system’s point of view, to know something about how each part contributes to making up the whole system. If you ignore for the moment all the wires and connections that link the various parts together, you will see the fundamental building blocks of all computer systems and subsystems — the integrated circuit chips. All the functional hardware parts of the computer — input, processor, storage, and output — can be made from integrated circuits. Working in close conjunction with the microprocessor is a form of storage called the computer’s memory. This is where the programs, along with the data to be input and the results to be output, are stored. ROM (read-only memory) is permanent memory from which the microprocessor can read information, but whose contents can be neither erased nor written over — thus the name, read-only memory. ROM stores the instructions that start up the computer when the power is turned on as well as some additional programs that need never be changed. RAM (random-access memory) is temporary memory that is empty until the microprocessor needs to use it, that is, until it loads programs and data into it. RAM is often called read/write memory, meaning that the microprocessor can read its contents and write programs or data into it. Most RAM is temporary because it loses its contents when the computer’s power is turned off. For long-term storage of information or programs, disk drives are connected to the system. Memories for personal computers are rated according to their capacity, which is measured in thousands or millions of bytes. A byte consists of eight consecutive bits and is the equivalent of one character, such as a letter, a number, or a punctuation mark. By themselves, the chips cannot do much — they have to be connected and fed with electricity. The chips are usually mounted on a system board or motherboard — a fiberglass circuit board that contains sockets into which the chips are plugged and a set of tracks (printed on the circuit board) that connects the various chips. Because these tiny integrated circuit chips require so little electricity to operate, a power supply is also housed in the system unit. This converts ordinary household current into the low-voltage direct current that the integrated circuits require. Many personal computers also contain a series of sockets, called expansion slots, into which additional circuit boards can be plugged. These additional circuit boards expand the capabilities of the computer. Some can contain additional memory chips, whereas others can provide the ability to connect additional external devices: for example, a modem, a printer, extra disc drives, or other input/ output devices, such as a colour display screen.
8. Answer the questions a. What does a system unit house? b. Where are the computer programs and data stored? c. What types of the computer’s memory do you know? d. What does “ROM” stand for? e. What is the difference between permanent and temporary memories? f. How are memories for personal computers measured? g. What are expansion slots used for?
9. Translate into English Системний блок, розділовий знак, змінний струм, постійний струм низької напруги, дисковод, резервна копія, запам’ятовувальний пристрій великої ємності, головка читання/запису, лазерний промінь, інтегральна схема, мікросхема, центральний процесор, оперативна пам’ять, тимчасова пам’ять, гніздо розширення, джерело електроживлення, зовнішній пристрій, забезпечувати доступ, вилучати, ємність, з’єднувати з системою, записувати інформацію, завантажити програму.
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