1. Chapter 15, Exploring the Digital Domain
Operating Systems
Chapter 15,
Exploring the Digital Domain

2. In this chapter . . .
You will learn about
how systems software and operating systems run the show
understanding how programs are brought to life and maintained as processes
The special functions of single-user and multiuser, multithreaded and multitasking operating systems

3. Operating Systems system software vs. application software
operating system is a collection of resident programs that
manage the computer’s resources
supervise the execution of users’ processes
provide useful services and security

4. Operating Systems
application programs employ OS services by means of system calls
a system call is a request to the OS to perform a specific service
e.g.s: finding, opening a file, allocating memory, transferring a file to the printer, etc.

5. Programs vs. Processes a program is a list of instructions
a program is usually written in a symbolic programming language
a program is a static entity
a process is a series of events
a process is a sequence of distinct states, i.e., operations performed by the processor
a process is dynamic

6. Single-User OS
single-user, single-programming OS executes only one process at time
chief functions
supervisor
I/O control drivers
memory manager
file manager
user interface

7. Supervisor
supervisor oversees the execution of system and user processes

8. Supervisor
system calls spawn kernel processes, privileged processes that only the OS can perform
the supervisor manages transitions between user and kernel processes by context switching

9. I/O Control Drivers
primitive input/output instructions that handle transfers between I/O devices and the CPU
I/O service routines allow the application to perform I/O using “logical” rather than “physical” requests

10. Memory Manager
has the responsibility for allocating segments of RAM for use by competing processes

11. Multiuser Operating System
allows multiple users to perform tasks with a single computer’s processor system
the multiuser OS interleaves the execution of instruction from a number of processes concurrently
multitasking

12. Multiuser Operating System
processes must be pooled and ready for processing
requires order and more memory
the multiuser OS is supported by
CPU scheduler
virtual memory

13. Virtual Memory
creates the illusion for the CPU that the usable memory address space is larger than physical memory

14. Multithreaded Operating System
supports concurrent multiple threads from the same or different processes
a thread (of execution) is a “lightweight” process
a function or separate task in an application
a distinct set of instructions that can be executed independently