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CHAPTER 2: OPERATING SYSTEM
STRUCTURES
OS SERVICES: THE BIG VIEW (1)
• User interface - Almost all operating systems have a user interface:
Command-Line, Graphics User Interface (GUI), Batch
• Program execution – load, run, executed, end execution
• I/O operations - Deal with I/O devices
• File-system manipulation - Programs need to read and write files
and directories, create and delete them, search them, list file Information,
permission management.
• Communications – Processes frequently exchange information
through message passing or shared memory
OS SERVICES: THE BIG VIEW (2)
• Error detection – OS needs to be constantly aware of possible errors: CPU,
memory, I/O devices and be able to take action
• Resource allocation - When multiple users or multiple jobs running
concurrently, resources must be allocated to each of them: CPU, RAM, files, I/O
devices
• Accounting - To keep track of which users use how much and what kinds of
computer resources
• Protection and security –
• Protection - ensure that all access to system resources is controlled
• Security – protect system from outside users
A VIEW OF OPERATING SYSTEM SERVICES
SYSTEM CALLS
• Programming interface to the services provided by the OS
• Typically written in a high-level language (C or C++)
• Mostly accessed by programs via a high-level Application
Programming Interface (API) rather than direct system
call use
• Three most common APIs are Win32 API for Windows,
POSIX API for POSIX-based systems (including virtually all
versions of UNIX, Linux, and Mac OS X), and Java API for the
Java virtual machine (JVM)
EXAMPLE OF SYSTEM CALLS
• System call sequence to copy the contents of one file to
another file
EXAMPLE OF STANDARD API
SYSTEM CALL IMPLEMENTATION
• The system call interface invokes the intended system call in OS
kernel and returns status of the system call and any return values
• The caller need know nothing about how the system call is
implemented
• Just needs to obey API and understand what OS will do as a result call
• Most details of OS interface hidden from programmer by API
API – SYSTEM CALL – OS RELATIONSHIP
TYPES OF SYSTEM CALLS
• Process control
• create process, terminate process
• end, abort
• load, execute
• get process attributes, set process attributes
• wait for time
• wait event, signal event
• allocate and free memory
• Dump memory if error
• Debugger for determining bugs, single step execution
• Locks for managing access to shared data between processes
TYPES OF SYSTEM CALLS
• File management
• create file, delete file
• open, close file
• read, write, reposition
• get and set file attributes
• Device management
• request device, release device
• read, write, reposition
• get device attributes, set device attributes
• logically attach or detach devices
TYPES OF SYSTEM CALLS (CONT.)
• Information maintenance
• get time or date, set time or date
• get system data, set system data
• get and set process, file, or device attributes
• Communications
• create, delete communication connection
• send, receive messages if message passing model to host name or
process name
• From client to server
• Shared-memory model create and gain access to memory regions
• transfer status information
• attach and detach remote devices
TYPES OF SYSTEM CALLS (CONT.)
• Protection
• Control access to resources
• Get and set permissions
• Allow and deny user access
EXAMPLES OF WINDOWS AND UNIX SYSTEM CALLS
SYSTEM CALL EXAMPLE
include <stdio.h>
#include <fcntl.h>
#include <sys/stat.h>
int main(int argc, char* argv[])
{
int inFile, outFile;
int len; char ch;
if (argc != 3)
{
printf("Usage: copy <f1> <f2>\n");
exit(1);
}
inFile = open(argv[1], O_RDONLY);
outFile = open(argv[2], O_WRONLY | O_CREAT, S_IRWXU);
while ((len = read(inFile, &ch, 1)) > 0)
{
write(outFile, &ch, 1);
}
close(inFile);
close(outFile);
return 0;
}
SINGLE-TASKING: MS-DOS
• Single-tasking
• Shell invoked when system
booted
• Simple method to run
program
• No process created
• Single memory space
• Loads program into memory,
overwriting all but the kernel
• Program exit -> shell
reloaded
At system startup
running a program
MULTITASKING: UNIX
• Multitasking
• User login -> invoke user’s choice of shell
• Shell executes fork() system call to create
process
• Executes exec() to load program into process
• Shell waits for process to terminate or
continues with user commands
• Process exits with:
•
code = 0 – no error
•
code > 0 – error code
TRADITIONAL UNIX SYSTEM STRUCTURE
SYSTEM BOOT
• When power initialized, execution starts at a fixed memory location
• Firmware ROM used to hold initial boot code
• Operating system must be made available to hardware so hardware
can start it
• Small piece of code – bootstrap loader, stored in ROM or EEPROM
locates the kernel, loads it into memory, and starts it
• Sometimes two-step process where boot block at fixed location loaded by
ROM code, which loads bootstrap loader from disk
• Common bootstrap loader, GRUB, allows selection of kernel from
multiple disks, versions, kernel options
• Kernel loads and system is then running
O/S MILESTONES (1)
• IBSYS
• Fifties
• Resident monitor
• IBM 1401/7094
• OS/360
•
•
•
•
Sixties
IBM 360
Multiprogramming
Frederick Brooks, The Mythical Man-Month
• CTSS (Conversational Timesharing System)
• Early sixties
• MIT for IBM 7098
• Early version of time sharing
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O/S MILESTONES (2)
• Multics
•
•
•
•
Mid sixties
MIT, Bell Labs, GE
Many seminal o/s ideas, time-sharing in particular
Idea of a computer utility
• OS/370
• Time sharing
• Virtual memory (but Manchester Atlas was first VM machine)
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O/S MILESTONES (3)
• Unix
• Ken Thompson worked on Multics
• He and Dennis Ritchie create a strippeddown, one user version of Multics
• Early seventies
• DEC PDP-7
• Later ported to a PDP-11: led to the idea that
an o/s does not have to be hardware specific
• PDP-11 version written in C (Kernighan and
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Ritchie)
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O/S MILESTONES (4)
• MS-DOS
• Early 80s
• Built for IBM to exploit mass-marketed 8086
• Preceded by CP/M (Gary Kildall, consultant to Intel)
• Minix
• Mid 80s
• Teaching version of Unix to run on intel processors
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O/S Milestones (4)
• Linux
• 90’s
• Fully-featured o/s
• Linus Thorvalds
Hello everybody out there using minix - I'm doing a (free) operating
system (just a hobby, won't be big and professional like gnu) for
386(486) AT clones. This has been brewing since april, and is starting
to get ready. I'd like any feedback on things people like/dislike in minix,
as my OS resembles it somewhat (same physical layout of the filesystem (due to practical reasons) among other things).
I've currently ported bash(1.08) and gcc(1.40), and things seem to
work. This implies that I'll get something practical within a few
months, and I'd like to know what features most people would want.
Any suggestions are welcome, but I won't promise I'll implement
them :-)
Linus ([email protected])
PS. Yes – it's free of any minix code, and it has a multi-threaded fs. It
is NOT portable (uses 386 task switching etc), and it probably never
will support anything other than AT-harddisks, as that's all I have :-(.
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O/S MILESTONES (5)
• Windowing Systems
• Doug Engelbart SRI, Xerox Parcmouse, windows etc.
• Steve Jobs saw it during a visit Macintosh
• Microsoft Windows in all of its incarnations
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OS MILESTONES (6)
• Virtual Machines
• Create the illusion of multiple operating systems running on the
same physical hardware
• IBM’s CP/CMS and VM/370 (early seventies)
• VirtualBox, VMware (current)
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OS MILESTONES (7)
• Mobile Computing
• 1990s: Combine personal digital assistant (PDA) and mobile phone
• Term “smartphone” coined in 1997
• Current Dominant OS
• Linux-based Android from Google
• iOS from Apple
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