This document discusses different types of software and operating system components. It describes applications software as performing machine-specific tasks and system software as performing common computer tasks that vary based on hardware. Utility software extends operating systems by providing fundamental but non-essential functions. The operating system shell defines the user interface, which can be graphical or command line-based. The kernel manages core OS functions like the file manager, device drivers, memory manager, scheduler, and dispatcher. The file manager organizes files, the device drivers communicate with hardware, the memory manager allocates memory, and the scheduler and dispatcher manage processes and processor time allocation.

1. Lecture # 3

2. Types of software
 Applications software
 Performs tasks specific to the machine’s utilization.
 Generally transportable
 System Software
 Performs tasks common to computer systems in general
 Operating systems vary based on the hardware they’re
used on

3. Types of software (cont’d)
 Utility software
 providing fundamental activities, yet not included with
OS
 “extend” the OS

4. The OS Shell
 Defines interface between OS and users
 Windows GUI
 UNIX command line
 UNIX users can choose among a variety of shells
 csh is the “C shell”
 tcsh is an enhanced “C shell”
 Shell programming

5. OS Shell interface
O / S
shell
Users
Users
Users

6. The OS Kernel
 The internal part of the OS is often called the Kernel
 Kernel Components
 File Manager
 Device Drivers
 Memory Manager
 Scheduler
 Dispatcher

7. OS File Manager
 Maintains information about the files that are
available on the system
 Where files are located in mass storage, their size and
type and their protections, what part of mass storage is
available
 Files usually allowed to be grouped in directories or
folders. Allows hierarchical organization.

8. OS Device Drivers
 Software to communicate with peripheral devices or
controllers
 Each driver is unique
 Translates general requests into specific steps for that
device

9. OS Memory Manager
 This unit is responsible for coordinating the use of the
machine’s main memory.
 It decides what area of memory is to be allocated for a
program and it’s data
 It allocates and deallocates memory for different
programs and always knows what areas are free.

10. OS Scheduler
 Maintains a record of processes that are present, adds
new processes, removes completed processes
 memory area(s) assigned
 priority
 state of readiness to execute (ready/wait)

11. OS Dispatcher
 Ensures that processes that are ready to run are
actually executed
 Time is divided into small (50 ms) segments called a
time slice.
 When the time slice is over, the dispatcher allows
scheduler to update process state for each process,
then selects the next process to run

12. The OS Kernel

13. OS Summary
 Shell -- interface to user
 File Manager -- manages mass memory
 Device Drivers -- communicate with peripherals
 Memory Manager -- manages main memory
 Scheduler & Dispatcher -- manage processes