Chapter 1. Computer System Overview

Chapter 1. Computer System Overview

An Operating system exploits the hardware resources of one or more processor to provide a set of services to system users. The operating system also manages secondary memory and I/O (input/output) devices on behalf of its users. Accordingly, it is important to have some understanding of the undelying computer system hardware we begin our examination of operating system.

Basic Elements

At top level, a computer consists of processor, memory, and I/O component with one or more modules of each type. These components are interconnected in some fashion to achieve the main function of the computer, which is to execute programs. Thus there are four main structural elements:

1. Processor : Controls the operating of the computer and performs its data processing function. When there is only one processor, it is often referred to as the central processing unit (CPU).
2. Main Memory: Stores data and programs. This memory is typically volatile; that is, when the computer is shut down, the contenst of the memory are lost. In contrast, the contents of disk memory are reatined even when the computer system is shutdown. Main memory is also referred to as real memory or primary memory.
3. I/O Moduls : Move data between the computer and its external environment. The external environtment consists of a variety of devices, including secondary memory devices, communications equipment, and terminals.
4. System bus L Provides for communication among processor, main memory, and I/O Modules.



Figure 1.1. Computer Components

One of the processor’s function is to exchange data with memory. For this purpose, it typically makes use of two internal (to the processor) register: a memory addres register (MAR(, whitch specifies the address in memory for the next read or write; and a memory buffer register (MBR), which contains the data to be written into memory or which receives the data read from memory. Similarly, an I/O address register (I/OAR) specifies a particular I/O device. An I/O buffer register (I/OBR) is used for the exchange of data between an I/O module and the Processor.

A memory module consists of a set of locations, defined by sequentially numbered addresses. Each location contains a bit pattern that can be interpreted as either an instruction or data. An I/O module transfers data from external devices to processor and memory, and vice versa. It contains internal buffers for temporrarily holding data until can be sent on.

Source :
William Stallings, “Operating Systems “Internals and Design Principles”, Fifth Edition, Pearson Education Internationl
Related Post :
Basic Elements
Processor Register
Intruction Execution
Interupts
The Memory Hierarchycal
Cace Memory
I/O Communication
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