I / Preface

Operating System ( OS ) covers all the fundamental principles in great detail , interprocess communication , semaphores , monitors , message passing , scheduling algorithm , input/output , deadlocks , device drivers , memory management , paging algorithms , file system design , security and protection mechanisms . But it also discusses one particular system MINIX 3a UNIX – compatible OS in detail and even provides a source code listing for study . This arrangement allows the reader not only to learn the principles , but also to see how they are applied in a real OS .

Its first 10 years , MINIX underwent many changes . The original code was designed for a 256K 8088 – based IBM PC with two diskette drivers and no hard disk .  It supported 32-bit protected mode machines with large memories and hard disks . It also changed from being based on Vesion 7 , to being based on the international POSIX standard ( IEEE 1003.1 and ISO 9945-1 ) . In addition, MINIX was ported to many other platforms, including the Macintosh, Amiga, Atari, and SPARC. A second edition of the book, covering this system, was published in 1997 and was widely used at universities.

The popularity of MINIX has continued , as can be observed by examining the number of hits for MINX found by Google .

The design of MINIX 3 was inspired by the observation that OS are becoming bloated , slow and unreliable .To a large extent, many of these problems are caused by a fundamental design flaw in current operating systems: their lack of modularity. The entire operating system is typically millions of lines of C/C++ code compiled into a single massive executable program run in kernel mode. A bug in any one of those millions of lines of code can cause the system to malfunction. Getting all this code correct is impossible, especially when about 70% consists of device drivers, written by third parties, and outside the purview of the people maintaining the operating system…..

II / Introduction 

Without its software , a computer is basically a useless lump of metal . With its software , a computer can store , process , and retrieve information , play music and videos , play music and videos , send e-mail, search the Internet , …

Computer software can be divided two kinds  : System programs , which manage of the operation of the most fundamental system program is the Operating System , whose job is to control all the computer’s resources and provide a base upon which the application programs can be written . In particular , an OS called MINIX 3 is used as a model to illustrate design principles and the realities of implementation a design .

A modern computer system consists of one or more processors, some main memory, disks, printers, a keyboard, a display, network interfaces, and other input/output devices. All in all, a complex system. Writing programs that keep track of all these components and use them correctly, let alone optimally, is an extremely difficult job.

A modern computer system consists of one or more processors, some main memory, disks, printers, a keyboard, a display, network interfaces, and other input/output devices. All in all, a complex system. Writing programs that keep track of all these components and use them correctly, let alone optimally, is an extremely difficult job.

 

The placement of the operating system is shown in Fig. 1-1. At the bottom is the hardware, which, in many cases, is itself composed of two or more levels (or layers). The lowest level contains physical devices, consisting of integrated circuit chips, wires, power supplies, cathode ray tubes, and similar physical devices. How these are constructed and how they work is the province of the electrical engineer.

Figure 1-1. A computer system consists of hardware, system programs, and application programs.

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Next comes the microarchitecture level, in which the physical devices are grouped together to form functional units. Typically this level contains some registers internal to the CPU (Central Processing Unit) and a data path containing an arithmetic logic unit. In each clock cycle, one or two operands are fetched from the registers and combined in the arithmetic logic unit (for example, by addition or Boolean AND). The result is stored in one or more registers. On some machines, the operation of the data path is controlled by software, called the microprogram. On other machines, it is controlled directly by hardware circuits.
The purpose of the data path is to execute some set of instructions. Some of these can be carried out in one data path cycle; others may require multiple data path cycles. These instructions may use registers or other hardware facilities. Together, the hardware and instructions visible to an assembly language programmer form the ISA (Instruction Set Architecture) This level is often called machine language.

The machine language typically has between 50 and 300 instructions, mostly for moving data around the machine, doing arithmetic, and comparing values. In this level, the input/output devices are controlled by loading values into special device registers. For example, a disk can be commanded to read by loading the values of the disk address, main memory address, byte count, and direction (read or write) into its registers. In practice, many more parameters are needed, and the status returned by the drive after an operation may be complex. Furthermore, for many I/O (Input/Output) devices, timing plays an important role in the programming.

A major function of the operating system is to hide all this complexity and give the programmer a more convenient set of instructions to work with. For example, read block from file is conceptually much simpler than having to worry about the details of moving disk heads, waiting for them to settle down, and so on.

On top of the operating system is the rest of the system software. Here we find the command interpreter (shell), window systems, compilers, editors, and similar application-independent programs. It is important to realize that these programs are definitely not part of the operating system, even though they are typically supplied preinstalled by the computer manufacturer, or in a package with the operating system if it is installed after purchase. This is a crucial, but subtle, point. The operating system is (usually) that portion of the software that runs in kernel mode or supervisor mode. It is protected from user tampering by the hardware (ignoring for the moment some older or low-end microprocessors that do not have hardware protection at all). Compilers and editors run in user mode. If a user does not like a particular compiler, he[ ] is free to write his own if he so chooses; he is not free to write his own clock interrupt handler, which is part of the operating system and is normally protected by hardware against attempts by users to modify it….

To be continue …

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