Operating

System

Brief history

Early computer systems

No OS

programmers aware of the underlying HW

no multitasking

one job at a time

IBM System 360

OS 360 (IBM) [1965]

multitasking

pagination

assembly

Brief history

Multics (MIT/General Electrics/Bell Labs) [1965]

PDP-7

memory mapped files

(sort of) virtual filesystem

process memory segments viewed as files

dynamic linking

multitasking

pagination

segmentation

interprocess calls

dropped

Brief history

Unix [1969]

PDP-7 (PDP-11 initially)

then widespread

C

preemptive multitasking

pagination

segmentation

Brief history

MS-DOS [1981]

no advanced features (lack of hw support)

Windows 3.1 [1992]

pagination

multitasking (no preemption)

Windows NT 3.1 [1993]

Linux [start: 1991 ver. 1.0 release: 1994]

Several others

� VAX/VMS, MAC-OS, OS/2, QNX, Symbian OS, ...

Features

Abstraction

HW details

Management

resources

Protection

Errors / attacks

Features

Program execution management

Security

User mode vs Supervisor/Protected/Kernel mode

Multitasking

Hardware management

Abstraction

Hardware driving

Interrupt handling

Memory management

Elements

Scheduler

Device drivers

Memory management routines

Cache (buffer) management

Operating System

Interface between applications and hardware

provides hardware abstraction (and protection)

Resource manager

Activity coordinator

Applications

Operating System

HARDWARE

User Level

Kernel Level

Protection

Kernel (or protected or supervisor) level

Full system access

HW devices registers

“Critical” address space regions

I/O mapping

System data

User level

Restricted system access

“Owned” address space regions

Interface

OS functions called by applications

Application Programming Interface (API)

standard routine call

library routine

Application

Library

OS

std call

Kernel level

User level

standard routine callApplication

Library

OSKernel level

User level

standard routine call

OS routineOS routine

Protection issue

func_enter_address:

<parameters validation>

<user permissions check>

func_internal_address:

<critical work>

Kernel level code

<parameters setting>

call func_enter_address

User code

OK

<parameters setting>

call func_internal_address

User codeNO(protection bypassed)

Interface

OS functions called by applications

Application Programming Interface (API)

standard routine call

system calls (syscalls)

not a standard function call

is the “door” for the kernel level

usually “wrapped” by library functions

open (library routine)

open (OS routine)

Application

Library

OS

libraries provide a

further abstraction

(abstraction from OS)

syscall

Kernel level

User level

standard routine call

System calls

Architecture dependent

software interrupt / trap

Call # Routine address

2

System routine

...

/* parameters in registers */

...

mov r7, 2 /* syscall no. */

SVC 0 /* syscall */

...

/* results managing */

...

user code

syscall table can be modified

only at kernel level

Example: ARM – Linux

System calls

Architecture dependent

software interrupt / trap

Call # Routine address

2

System routine

...

/* parameters in registers */

...

SVC 2 /* syscall */

...

/* results managing */

...

user code

syscall table can be modified

only at kernel level

Example: ARM – Linux (old ABI)