OPERATING SYSTEMS
B-Eng, Computer Engineering Year
II / Semester II
1. INTRODUCTION TO OPERATING SYSTEMS AND OVERVIEW OF
COMPUTER SYSTEM
What is an Operating System?
An operating system is collection of system programs that together control
the operations of a computer system, acts as an intermediary between the
user of a computer and the hardware, through application program. Some
examples of operating systems are UNIX, Mach, MS-DOS, MSWindows,
Windows/NT, Chicago, OS/2, MacOS, VMS, MVS, and VM Operating
system goals:
• Execute user programs and make solving user problems easier
• Make the computer system convenient to use
• Use the computer hardware in an efficient manner
,Operating systems are tightly coupled with the architecture of the
computer on which they are running. Some background on how the
hardware works is therefore required.
Computer System Structure
Computer system can be divided into four components
• Hardware : provides basic computing resources
- CPU, memory, I/O devices
• Operating system
- Controls and coordinates use of hardware among various
applications and users
• Application programs : define the ways in which the system
resources are used to solve the computing problems of the users -
Word processors, compilers, web browsers, database systems,
video games
• Users
- People, machines, other computers
The diagram below shows how the four components of a computer system
interact together.
An Operating System
• is a resource allocator,
• Manages all resources,
• Decides between conflicting requests for efficient and fair resource use
• is a control program
• Controls execution of programs to prevent errors and improper use
of the computer
COURSE
FACILITATOR : TATSOPTEU E. ENDELLY
1
, • “The one program running at all times on the computer” is the
kernel. Everything else is either a system program (ships with the
operating system) or an application program.
Computer Startup (System Boot) / Operating System Generation
• Operating systems are designed to run on any of a class of
machines, and must be made available to hardware so it can start it
• SYSGEN program obtains information concerning the specific
configuration of the hardware system
• Booting : starting a computer by loading the kernel
• Bootstrap program : code stored in ROM (firmware) that is able to
locate the kernel, load it into memory, and start its execution
Computer System Organization
• One or more CPUs, device controllers connect through common bus
providing access to shared memory
• Concurrent execution of CPUs and devices competing for memory
cycles
Computer-System Operation
• I/O devices and the CPU can execute concurrently
• Each device controller is in charge of a particular device type
• Each device controller has a local buffer
• CPU moves data from/to main memory to/from local buffers
• I/O is from the device to local buffer of controller
• Device controller informs CPU that it has finished its operation by
causing An interrupt
Interrupts
An interrupt is a hardware mechanism that enables an external device,
typically I/O devices, to send a signal to the CPU. An interrupt signal
COURSE
FACILITATOR : TATSOPTEU E. ENDELLY
2
, requests the CPU, to interrupt its current activities and attend to the
interrupting device’s needs.
Direct Memory Access Structure
The main idea of direct memory access (DMA) is to enable peripheral
devices to cut out the “middle man” role of the CPU in data transfer. It
allows peripheral devices to transfer data directly from and to memory
without the intervention of the CPU. Having peripheral devices access
memory directly would allow the CPU to do other work, which would lead
to improved performance, especially in the cases of large transfers. The
features of DMA are presented below:
• Used for high-speed I/O devices able to transmit information at close
to memory speeds
• Device controller transfers blocks of data from buffer storage directly
to main memory without CPU intervention
• Only one interrupt is generated per block, rather than the one
interrupt per byte.
Storage Structure
• Main memory: only large storage media that the CPU can access directly
• Secondary storage: extension of main memory that provides large
non-volatile storage capacity
• Magnetic disks: rigid metal or glass platters covered with magnetic
recording material
• Disk surface is logically divided into tracks, which are subdivided into sectors
• The disk controller determines the logical interaction between the
device and the computer
Storage Hierarchy
Storage systems organized in:
• hierarchy
• Speed
• Cost
• Volatility
COURSE
FACILITATOR : TATSOPTEU E. ENDELLY
3
B-Eng, Computer Engineering Year
II / Semester II
1. INTRODUCTION TO OPERATING SYSTEMS AND OVERVIEW OF
COMPUTER SYSTEM
What is an Operating System?
An operating system is collection of system programs that together control
the operations of a computer system, acts as an intermediary between the
user of a computer and the hardware, through application program. Some
examples of operating systems are UNIX, Mach, MS-DOS, MSWindows,
Windows/NT, Chicago, OS/2, MacOS, VMS, MVS, and VM Operating
system goals:
• Execute user programs and make solving user problems easier
• Make the computer system convenient to use
• Use the computer hardware in an efficient manner
,Operating systems are tightly coupled with the architecture of the
computer on which they are running. Some background on how the
hardware works is therefore required.
Computer System Structure
Computer system can be divided into four components
• Hardware : provides basic computing resources
- CPU, memory, I/O devices
• Operating system
- Controls and coordinates use of hardware among various
applications and users
• Application programs : define the ways in which the system
resources are used to solve the computing problems of the users -
Word processors, compilers, web browsers, database systems,
video games
• Users
- People, machines, other computers
The diagram below shows how the four components of a computer system
interact together.
An Operating System
• is a resource allocator,
• Manages all resources,
• Decides between conflicting requests for efficient and fair resource use
• is a control program
• Controls execution of programs to prevent errors and improper use
of the computer
COURSE
FACILITATOR : TATSOPTEU E. ENDELLY
1
, • “The one program running at all times on the computer” is the
kernel. Everything else is either a system program (ships with the
operating system) or an application program.
Computer Startup (System Boot) / Operating System Generation
• Operating systems are designed to run on any of a class of
machines, and must be made available to hardware so it can start it
• SYSGEN program obtains information concerning the specific
configuration of the hardware system
• Booting : starting a computer by loading the kernel
• Bootstrap program : code stored in ROM (firmware) that is able to
locate the kernel, load it into memory, and start its execution
Computer System Organization
• One or more CPUs, device controllers connect through common bus
providing access to shared memory
• Concurrent execution of CPUs and devices competing for memory
cycles
Computer-System Operation
• I/O devices and the CPU can execute concurrently
• Each device controller is in charge of a particular device type
• Each device controller has a local buffer
• CPU moves data from/to main memory to/from local buffers
• I/O is from the device to local buffer of controller
• Device controller informs CPU that it has finished its operation by
causing An interrupt
Interrupts
An interrupt is a hardware mechanism that enables an external device,
typically I/O devices, to send a signal to the CPU. An interrupt signal
COURSE
FACILITATOR : TATSOPTEU E. ENDELLY
2
, requests the CPU, to interrupt its current activities and attend to the
interrupting device’s needs.
Direct Memory Access Structure
The main idea of direct memory access (DMA) is to enable peripheral
devices to cut out the “middle man” role of the CPU in data transfer. It
allows peripheral devices to transfer data directly from and to memory
without the intervention of the CPU. Having peripheral devices access
memory directly would allow the CPU to do other work, which would lead
to improved performance, especially in the cases of large transfers. The
features of DMA are presented below:
• Used for high-speed I/O devices able to transmit information at close
to memory speeds
• Device controller transfers blocks of data from buffer storage directly
to main memory without CPU intervention
• Only one interrupt is generated per block, rather than the one
interrupt per byte.
Storage Structure
• Main memory: only large storage media that the CPU can access directly
• Secondary storage: extension of main memory that provides large
non-volatile storage capacity
• Magnetic disks: rigid metal or glass platters covered with magnetic
recording material
• Disk surface is logically divided into tracks, which are subdivided into sectors
• The disk controller determines the logical interaction between the
device and the computer
Storage Hierarchy
Storage systems organized in:
• hierarchy
• Speed
• Cost
• Volatility
COURSE
FACILITATOR : TATSOPTEU E. ENDELLY
3
