Overview and Introduction to
Computing Systems
Fred Kuhns
Bryan504
fredk@cs.wustl.edu
Introduction
• A computer system consists of
– hardware
– system programs
– application programs
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What is an Operating System
• It is an extended machine (Presents a
Convenient Interface to users)
– Hides the messy details which must be
performed
– Presents user with a virtual machine, easier
to use
• It is a resource manager
– Each program gets time with the resource
– Each program gets space on the resource
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History of Operating Systems
Early batch system
–
–
–
–
bring cards to 1401
read cards to tape
put tape on 7094 which does computing
put tape on 1401 which prints output
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History of Operating Systems
• First generation 1945 - 1955
– vacuum tubes, plug boards
• Second generation 1955 - 1965
– transistors, batch systems
• Third generation 1965 – 1980
– ICs and multiprogramming
• Fourth generation 1980 – present
– personal computers
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History of Operating Systems
• Structure of a typical FMS job – 2nd
generation
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History of Operating Systems
• Multiprogramming system
– three jobs in memory – 3rd generation
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Current “Specialized” OSes
•
•
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•
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Mainframe operating systems
Server operating systems
Multiprocessor operating systems
Personal computer operating systems
Real-time operating systems
Embedded operating systems
Smart card operating systems
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Basic Hardware Elements
• Processor - traditionally controls the
operation of the computer and
performs the data processing function
• Memory - Stores data and programs,
typically volatile (aka real or primary
memory)
• I/O modules - move data between
computer and external environment (i.e.
disks, network)
• System Bus - communication among
processors, memory, and I/O modules
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Computer Hardware Review
Monitor
Bus
• Components of a simple personal computer
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Computer Components: Another view
CPU
PC
MAR
IR
MBR
Memory
..
.
Instruction
Instruction
Instruction
..
.
Data
Data
Data
Data
..
.
I/O AR
execution
unit
I/O BR
I/O Module
..
Buffers
N
PC - Program Counter
IR - Instruction Register
MAR - Memory Address Register
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0
1
MBR - Memory Buffer Register
I/O AR - Input/Output Address Register
I/O BE - Input/Output Buffer Register
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Control and Status Registers
• Program Counter (PC)
– Contains the address of an instruction to be
fetched
• Instruction Register (IR)
– Contains the instruction most recently
fetched
• Program Status Word (PSW)
– condition codes
– Interrupt enable/disable
– Supervisor/user mode
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Instruction Cycle
• Processor fetches instruction from
memory
• PC contains address of next instruction
to be fetched
• PC incremented after each fetch
Fetch Cycle
START
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Fetch Next
Instruction
Execute Cycle
Execute
Instruction
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Modern Instruction Cycle
(a) A three-stage pipeline
(b) A superscalar CPU
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Typical memory hierarchy
• numbers shown are rough approximations
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Going Down the Hierarchy
•
•
•
•
Decreasing cost per bit
Increasing capacity
Increasing access time
Decreasing frequency of access of the
memory by the processor
– exploit locality of reference
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Cache/Main-Memory Structure
Slot
Number Tag
Memory
Address
0
1
2
3
Block
(k words)
Block
0
1
2
C - 1
Block Length
(k words)
(b) Cache
Block
2n - 1
Word Length
(a) Main Memory
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Cache Design
• Write policy
– keeping cache and main memory consistent
• Mapping function
– determines which cache location block
occupies
• Replacement algorithm
– determines which block to replace (LRU)
• Block size
– data unit exchanged between cache and
main memory
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Structure of a disk drive
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Multiprogramming and Addressing
• program addresses are relative to Base Address
• MMU maps virtual to physical address
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I/O Techniques
• Programmed I/O
– Processor does all the work. Poll for results.
• Interrupt Driven I/O
– Device notifies CPU when I/O operation
complete
• Direct memory access (DMA)
– DMA controller performes “Programmed
I/O”, not CPU.
– CPU notified with DMA complete
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I/O Operations and Interrupts
(a)
(b)
(a) Steps in starting an I/O and receiving interrupt
(b) How the CPU is interrupted
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Instruction Cycle with Interrupts
Interrupt Cycle
Execute Cycle
Interrupts Disabled
START
Fetch Next
Instruction
Execute
Instruction
Interrupts Enabled
Fetch Cycle
Check for &
Process Int
HALT
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Buses
• Structure of a large Pentium system
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Basic Operating System Concepts
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Processes
Deadlocks
Memory Management
Input/Output
Files
Security
The Shell
Policy versus Mechanism
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What is A Process?
• A process is a program in execution. A
process needs resources (CPU time,
memory, files, I/O devices) to
accomplish task.
• Process management activities:
– creation and deletion.
– suspension and resumption.
– Mechanisms for synchronization,
communication and deadlock handling
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Processes - An Introduction
• A process tree
– A created two child processes, B and C
– B created three child processes, D, E, and F
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Process Memory Space
• Processes have three segments: text, data, stack
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Deadlock - An Introduction
(a) A potential deadlock. (b) an actual deadlock.
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Example File System Structure
File system for a university department
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File Systems
• Before mounting,
– files on floppy are inaccessible
• After mounting floppy on b,
– files on floppy are part of file hierarchy
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Inter-Process Communication
Two processes connected by a pipe
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System Calls
• Interface between running program and
the operating system
– Generally written in assembly-language
– Wrapper libraries provide high-level interface
• Three general methods are used to pass
parameters:
– Pass parameters in registers.
– Store the parameters in a table in memory.
– Push (store) the parameters onto the stack by
the program.
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Steps in Making a System Call
There are 11 steps in making the system call
read (fd, buffer, nbytes)
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Some System Calls For Process Management
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Some System Calls For File Management
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Some System Calls For Directory Management
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Some System Calls For Miscellaneous Tasks
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System Calls - Process Management
• A stripped down shell:
while (TRUE) {
/* repeat forever */
type_prompt( );
/* display prompt */
read_command (command, parameters) /* input from terminal */
if (fork() != 0) {
/* Parent code */
waitpid( -1, &status, 0);
*/
} else {
/* Child code */
execve (command, parameters, 0);
}}
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/* fork child process */
/* wait for child to exit
/* execute command */
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System Calls
(a) Two directories before linking
/usr/jim/memo to ast's directory
(b) The same directories after linking
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System Calls
(a) File system before the mount
(b) File system after the mount
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System Calls
Some Win32 API calls
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Monolithic Design
Simple structuring model for a monolithic system
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Layered Design
Structure of the THE operating system
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Virtual Machines
Structure of VM/370 with CMS
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Client-Server Model
The client-server model
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Microkernel Design
The client-server model in a distributed
system
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Policy Versus Mechanism
• Policy (What) - Specifies desired
behavior or What should occur
• Mechanisms (How) - how the policy is
carried out - implementation of core
processing.
• The separation of policy from mechanism
is a very important principle, it allows
maximum flexibility if policy decisions
are to be changed later.
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Metric Units
The metric prefixes
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