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OPERATING SYSTEMOVERVIEW
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Contents
Basic hardware elements
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!Most I/O devices
are much slower thanthe processor
Interrupts
!Interrupt request signal
!Active waiting cycle(polling)
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! An interrupt cycle isadded to the instruction
cycle (fecth and execute).! The processor checks tosee if an interrupt hasoccured (interrupt signal)
Interrupt mechanism
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! interrupt handler
! interrupt vector
Interrupt mechanism
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! CPU saves PS and PC(push) into the control
stack
! CPU loads into PC andPS the corresponding
values from theinterrupt vector
Interrupt processing
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!iret
!interrupt handler
execution
Interrupt processing
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Interrupt enable/disablebit (PS register)
!Hardware priority
!STI (Set Interrupt)CLI (Clear Interrupt)
Interrupt mechanism
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main
ain
memory
emory
i+1 PS inth
1OO
OO
149
15O
iret
1OOO
12OO
12O1
main
ain
memory
emory
inth
nth
progrog
interrupt
nterrupt
1
2
3
interrupt
nterrupt
vector
ector
Interrupt processing
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PS prog
12O1
3824
PS
PC
SP
stack
main
memory
3824
39OO
CPU completes execution
of the current instruction
Interrupt processing
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interrupt signal has beenaccepted
PS inth
1OO
3822
PS
PC
SP
stack
main
ain
memory
emory
3824
39OO
12O1
PS prog
3823
3822
Interrupt processing
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PS inth
151
3822
PS
PC
SP
stack
main memory
ain memory
3824
39OO
12O1
PS prog
3823
3822
iret execution
Interrupt processing
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stack
main
memory
3824
39OO
PS prog
12O1
3824
PS
PC
SP
iret completed
Interrupt processing
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!Process Management
O.S. COMPONENTS
!Main-Memory Management
!Secondary-MemoryManagement
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!File Management
!I/O-System Management
O.S. COMPONENTS
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! Creating and deletingprocesses
! Suspending and resumingprocesses
! Provide mechanisms
for process interaction
Process management
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Keeping track of which
parts of memoryare currently being usedand by whom
Main memory management
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Deciding which processes
are to be loaded whenmemory becomes available
Main memory management
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Allocating and
deallocating memoryspace as needed
Main memory management
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Secondary memorymanagement
! Free space management! Storage allocation
! Disk scheduling
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I/O SYSTEM MANAGEMENT
The I/O subsystemconsists of
! A memory-managementcomponent that includesbuffering and spooling
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! A general device driverinterface
! Drivers for specific
hardware devices
I/O SYSTEM MANAGEMENT
The I/O subsystemconsists of
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File management
! Creating and deleting
files and directories! Supporting primitives
for manipulating fileand directory
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! Mapping files
onto storage! Backing up files
on stable storage media
File management
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Protection systems
! Mechanism for
controlling the accessof processes to systemresources
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! The mechanism must
provide means forspecifying the controlsto be imposed and meansfor enforcement
Protection systems
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! The interface betweenusers and O.S.
! A program that readsand interpretes controlstatements
Comand-Interpreter System
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! Its main function: to get
next command statementand execute it (shell)
Comand-Interpreter System
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System calls
Contents
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Processes communicate
with the O.S. and requestservices to it by makingsystem calls
System Calls
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System calls provide
the interface between anyprocess and O.S.
System Calls
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!Process control
Examples of System Call
!Communications
!Information management
!Device
manipulation
!File manipulation
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Corresponding to
each system call
there is a library procedure
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count= read file, buffer,
nbytes)
count returns the number of bytes
actually read
C program
Example:xample: readead system callystem call
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Library read
ibrary read
procedurerocedure
operating
perating
systemystem
system call
READ
INT
NT
return
eturn
from INT
rom INT
register x
x call
parameters
load x
system call
READ
2
3
1
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" Puts the parameters of the
system call in machine
registers
The library procedure
he library procedure
" The control is returned to
the caller by returning the
status code as a result
" Issues a INT instruction to
start the O.S.
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" directly via registers
" in a memory block whose
address is passed as a
parameter in a registry
" into the stack push, pop)
Methods to pass parameters to
operating system
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hardware
CPU, memory, disks, terminals, …)
UNIX O.S.
process management, memory
management, file system, I/O, ...)
standard library
open, close, read, write, ..)
utility programs
shell, compiler, …)
users
user
mode
kernel
mode
user
int.
library
interface
system
call
interf.
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Dual mode of operations
user mode
" Hardware control does not
allow the execution of
privileged instructions
" Used for normal execution of
user programs
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"" Used for the execution of
sed for the execution of
O.S. functions as required
.S. functions as required
by system calls
y system calls
supervisor mode kernel mode)
"" All instructions can be
ll instructions can be
executedxecuted
Dual mode of operations