CHỦ ĐIỂM 1.1. COMPUTER STRUCTURES Cấu trúc máy tính
Most computer systems generally consist of three basic structures or absystems: the high-speed memory unit, the central processing unit, and ne peripheral devices that comprise the I/O subsystem (see Fig 1-1).
Fig. 1-1 Basic computer structure.
1.1 The Memory Unit – Bộ nhớ
The memory unit of the computer, also called main memory or physical memory, stores all the instructions and data that the central processing nit can directly access and execute. The memory of majority of computers onsists of chips made of metal oxide on silicon. This type of memory is Iso called Kandom Access Memory or RAM.
The memory of the computer is generally divided into logical units of he same size. The most common unit is called a byte. Each byte is made p of 8 consecutive bits or binary digits (see Fig. 1-2). Each individual bit an be magnetized to one of two different states, hence the name of binary. One state is said to represent 1, the other represents 0. Sometimes, these wo states are referred to as “On” and “Off” respectively.
Each byte has associated with it a unique address. According to the convention used, addresses can increase from right to left or left to right see Fig. 1-3). In this book we will assume that addresses increase from ight to left unless we specify otherwise. The address space is the set of all unique addresses that a program can reference. The number of bite used to represent an address determines the size of the address space. The size of this snace can be calculated by 2 where N is the number of bits used represent the address. It is important to observe that there is a differenc between the address of a memory unit and the content of that unit. Th address of a byte is fixed whereas its content may vary.
