Module 3: Operating-System Structures
• System Components
• Operating System Services
• System Calls
• System Programs
• System Structure
• Virtual Machines
• System Design and Implementation
• System Generation
Common System Components
• Process Management
• Main Memory Management
• Secondary-Storage Management
• I/O System Management
• File Management
• Protection System
• Command-Interpreter System
• A process is a program in execution. A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task. • The operating system is responsible for the following activities in connection with process management.
– Process creation and deletion.
– process suspension and resumption.
– Provision of mechanisms for:
; process synchronization
; process communication
• Memory is a large array of words or bytes, each with its own address. It is a repository of quickly accessible data shared by the CPU and I/O devices. • Main memory is a volatile storage device. It loses its contents in the case of system failure.
• The operating system is responsible for the following activities in connections with memory management:
– Keep track of which parts of memory are currently being used and by
– Decide which processes to load when memory space becomes
– Allocate and deallocate memory space as needed.
• Since main memory (primary storage) is volatile and too small to
accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory.
• Most modern computer systems use disks as the principle on-line storage medium, for both programs and data.
• The operating system is responsible for the following activities in connection with disk management:
– Free space management
– Storage allocation
– Disk scheduling
I/O System Management
• The I/O system consists of:
– A buffer-caching system
– A general device-driver interface
– Drivers for specific hardware devices
• A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data.
• The operating system is responsible for the following activities in connections with file management:
– File creation and deletion.
– Directory creation and deletion.
– Support of primitives for manipulating files and directories.
– Mapping files onto secondary storage.
– File backup on stable (nonvolatile) storage media.
• Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources. • The protection mechanism must:
– distinguish between authorized and unauthorized usage.
– specify the controls to be imposed. //定義法律
– provide a means of enforcement. //執行法律
Networking (Distributed Systems)
• A distributed system is a collection processors that do not share memory or a clock. Each processor has its own local memory.
• The processors in the system are connected through a communication network.
• A distributed system provides user access to various system resources. • Access to a shared resource allows:
– Computation speed-up
– Increased data availability
– Enhanced reliability
• Many commands are given to the operating system by control statements which deal with:
– process creation and management
– I/O handling
– secondary-storage management
– main-memory management
– file-system access
Command-Interpreter System (Cont.)
• The program that reads and interprets control statements is called variously:
– control-card interpreter
– command-line interpreter
– shell (in UNIX)
Its function is to get and execute the next command statement.
Operating System Services
• Program execution – system capability to load a program into memory and to run it.
• I/O operations – since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O. • File-system manipulation – program capability to read, write, create, and delete files.
• Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing.
• Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.
Additional Operating System Functions
Additional functions exist not for helping the user, but rather for ensuring efficient system operations.
• Resource allocation – allocating resources to multiple users or multiple
jobs running at the same time.
• Accounting – keep track of and record which users use how much and
what kinds of computer resources for account billing or for accumulating
• Protection – ensuring that all access to system resources is controlled.
• System calls provide the interface between a running program and the operating system.
– Generally available as assembly-language instructions. – Languages defined to replace assembly language for systems
programming allow system calls to be made directly (e.g., C. Bliss,
• Three general methods are used to pass parameters between a running program and the operating system.
– Pass parameters in registers.
– Store the parameters in a table in memory, and the table address is
passed as a parameter in a register.
– Push (store) the parameters onto the stack by the program, and pop off
the stack by operating system.
Passing of Parameters As A Table
At System Start-up Running a Program
UNIX Running Multiple Programs
Msg Passing Shared Memory
.(a)like client-sever method. (b)should open the addressing constraint.
System Programs (SP)
• System programs provide a convenient environment for program development and execution. The can be divided into:
– File manipulation
– Status information
– File modification
– Programming language support
– Program loading and execution
– Application programs
• Most users’ view of the operation system is defined by system programs, not the actual system calls.
System Structure – Simple Approach
• MS-DOS – written to provide the most functionality in the least space
– not divided into modules
– Although MS-DOS has some structure, its interfaces and levels of
functionality are not well separated
MS-DOS Layer Structure
System Structure – Simple Approach (Cont.)
• UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts. – Systems programs
– The kernel
; Consists of everything below the system-call interface and above the
; Provides the file system, CPU scheduling, memory management, and
other operating-system functions; a large number of functions for one
UNIX System Structure
System Structure – Layered Approach
• The operating system is divided into a number of layers (levels), each built
on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.
• With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.
An Operating System Layer
Layered Structure of the THE OS
• A layered design was first used in THE operating system. Its six layers are as follows:
layer 5: user programs
layer 4: buffering for input and output
layer 3: operator-console device driver
layer 2: memory management
layer 1: CPU scheduling
layer 0: hardware
OS/2 Layer Structure
.Microkernels: removing all nonessential componets from the kernel, and implementing them as system programs.
.The main function of microkernel is to provide a communication facility between the client program and the various services that are also running in user space. .For example, client interact with the file server indirectly by exchanging messages with the microkernel.
-easy of extending the O.S., not require modification of kernel
-more security and reliablity
.Windows NT uses a hybrid structure. It is designed to run various applications, including WIN32, OS/2, and Posix. (如圖)
Windows NT Client-Server Structure
• A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware.
• A virtual machine provides an interface identical to the underlying bare
• The operating system creates the illusion of multiple processes, each executing on its own processor with its own (virtual) memory.
Virtual Machines (Cont.)
• The resources of the physical computer are shared to create the virtual machines.
– CPU scheduling can create the appearance that users have their own
– Spooling and a file system can provide virtual card readers and virtual
– A normal user time-sharing terminal serves as the virtual machine