Operating Systems
Software in the Background
- A set of programs that control all computer functions - commanding
resources, executing programs, and managing memory and data.
- Manage the hardware efficiently
- Support applications
- Establish a user interface
- Most common operating system for IBM and IBM compatible PCs.
- Developed by Microsoft for the first IBM PC.
- Booting the system means loading the operating system into
memory.
- The word booting is used because the operating system seems
to pull itself up by its own bootstraps.
- A small program in ROM loads the basic components of the operating
system from disk during booting.
DOS and Disk Drives
- When there are two diskette drives, they are called drives
A and B
- A hard drive is called drive C
- Additional hard drives, CD-ROM and network drives can take
on the letters D through Z
- The operating environment is the area in which the user works.
- Command-line interface - the user types commands to
direct the operating system.
- Shells - the user chooses commands from menus.
- Graphical User Interfaces (GUIs) - utilize a mouse
and
- icons (pictures representing files and programs).
- Gesture-Based Interface - gestures made on a tablet
with a stylus.
- Files are stored in groups called directories
- Directories are represented by folders in Windows
Windows 95
- Newest version of Windows is a full featured operating system,
not just an operating environment.
- It is backward compatible with DOS and Windows 3.1
programs.
- Supports plug and play - a standard that allows components
to be automatically configured.
Network Operating Systems
- Allows computers on a network to share resources such as hard
disks and printers.
- Also supports data security.
Resource Allocation
- The process of assigning resources to certain programs for
their use and deallocating them when the program using them is
finished, then reallocating them elsewhere.
- The concurrent use of one machine by several people.
- A common approach is to give each user a time slice during
which the computer works on the user's task.
Memory Management
- The process of allocating memory to programs and of keeping
the programs in memory separate from each other.
- Large computers often divide their memory into foreground
and background areas, based on priority.
- Virtual memory means that part of the program is stored on
disk and is brought into memory for execution only as needed.
- Paging is the process of dividing a program into equal-size
pieces called pages and storing them in memory spaces called page
frames.
- Memory protection is the process of keeping one program from
straying into memory used by another program.
- UNIX is a generic operating system - it works on more than
one manufacturer's computer system.
- Developed in 1971 by Ken Thompson and Dennis Richie at AT&T's
Bell laboratories.
- UNIX was given free of charge to many colleges and universities
in the late 1970s, partly because AT&T wasn't allowed to sell
software.
Execution of two or more programs concurrently (not simultaneously
) - the CPU processes part of one job, then part of the next,
etc..
- Implemented through a system of interrupts.