1. Chapter 2: Operating System Structures

2. 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

3. 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

4. A View of Operating System Services

5. 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)

6. Example of System Calls
System call sequence to copy the contents of one file to another file

7. Example of Standard API

8. 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

9. API – System Call – OS Relationship

10. 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

11. Types of System Calls File management Device management
create file, delete file
open, close file
read, write, reposition
get and set file attributes
Device management
request device, release device
get device attributes, set device attributes
logically attach or detach devices

12. 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

13. Types of System Calls (Cont.)
Protection
Control access to resources
Get and set permissions
Allow and deny user access

14. Examples of Windows and Unix System Calls

15. 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;

16. Single-tasking: MS-DOS
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

17. 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

18. Traditional UNIX System Structure

19. 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

20. O/S Milestones (1) IBSYS OS/360
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
11/28/2017

21. O/S Milestones (2) Multics OS/370 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)
11/28/2017

22. O/S Milestones (3) Unix Ken Thompson worked on Multics
He and Dennis Ritchie create a stripped- down, 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 Ritchie)
11/28/2017

23. O/S Milestones (4) MS-DOS Minix 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
11/28/2017

24. 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 file-system (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   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 :-(.
11/28/2017

25. 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
11/28/2017

26. 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)
11/28/2017

27. 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
11/28/2017