Operating Systems

What are Operating Systems

The operating system is the heart of the computer. It brings or "integrates" the hardware and applications together by supporting:

	How data is stored and retrieved from disks and other media.
	How the mouse, keyboard, joysticks, and other devices allow a user to enter or access data.
	How the computer display presents information.
	How the computer links to/works with other devices (printers, etc.) and computers via networks.
	How programs are developed for a particular computer.

Although operating systems tend to be hardware/platform specific (e.g., for the Macintosh, Unix, or 80X86 platform), they can generally be viewed at three levels:

BIOS (Basic Input/Output System)

	Fundamental to all computers.
	Enables basic user interface (input/output device), access to storage and the processor.
	Typically activated at computer start-up or boot.
	May be overridden by higher level functions.

DOS (Disk Operating System)

	Loaded following BIOS.
	Typically installed on disk system.
	May include enhancements to input and output functions (e.g., screen resolution, keyboard add-ons).
	Key purpose: define and manage computer data; typically via files.
	Typical file management structure: hierarchical (directories/folders).
	New variations: handheld devices, MP3 players and similar devices also need to manage files (usually a simpler file management system).
	DOS also provides interface to run programs (locate and start the program, provide file resources).
	Typical user interface is alphanumeric (keyboard driven) with command line access to DOS; display is text only (typically 25 lines by 80 characters).
	May also include memory management features (extended memory access).

Windowing System (Advanced Graphical Interface)

	User perspective: common user interface for multiple applications (windows, menus, message boxes, etc.).
	Very high density pixel-based graphics display (pixels are points of color in large X-Y coordinate space, typically 4:3 ratio - 640X480, 800X600, etc.).
	Mouse-based user interface based on rapid access to graphics display and interaction via click/double click.
	Additional features include: network file access, multi-tasking (multiple programs appearing to operate simultaneously), advanced graphics, common function management (printers, file management, etc.), advanced memory management.

The following chart outlines some of the key functions performed at each level of standard commercial operating system products.

Level

Product Examples

Descriptions

(these will vary depending on products)

BIOS

	Platform specific
	Originally never changed without hardware upgrade, now updateable
	Vendors: Phoenix , AMI, others

	Starts when the computer is initially activated.
	Performs startup tests to verify keyboard, monitor, and memory are operational.
	Verifies disk media is available to load DOS.
	Often provides access to hardware setup information.
	Limited program interface ability (often to a control panel for a program boot interface).

DOS

	MS-DOS (Microsoft DOS)
	IBM DOS
	Linux
	Unix

	Loaded by the BIOS from the hard drive or floppy.
	Establishes the ability for the computer to read/write disk media.
	Extends use of the memory (beyond 1 MB), keyboard, mouse, display and other hardware.
	Provides limited program interaction-typically command line interface (may include multiple lines of text and characters).

Windowing System or Graphical User Interface (GUI)

	Microsoft Windows 3.X, 95, 98, NT, ME, XP
	Macintosh
	X-Windows, Motif (UNIX)

	Loaded by DOS.
	Provides a standardized, graphical interface for program execution.
	Enables multiple program execution (multitasking) and interaction (clipboards, OLE).
	Extended memory and device interface features.
	Standardized system functions for printers and networks.
	Provides system level functions (application programming interface) for common program operations.
	Interface: highly graphical and mouse driven; provide very high density of data presentation and program control.

Operating System Components

The following differs from the previous perspective in that it presents a functional view of operating systems:

Operating System (OS) Layer

Description

Applications

Programs written on top of the OS.

e.g., word processors, spreadsheets, we browsers, etc.. Includes programs for creating other programs.

System Utilities

Includes OS management and control programs such as the Windows Control Panel (e.g., setting up printers, network access, etc.).

System Services

Built-in or added "higher-level" supporting software drivers that are available to applications.

e.g., digital audio/video drivers and compressors (AVI, Quicktime), database support (ADO, SQL, query tools)

Command Shell

Used for processing scripts, as well as commands typed at the keyboard. Scripts (e.g., DOS batch, Perl) often consist of commands for processing data as well as executing system programs and processes.

Graphical User Interface

Manages user access to the system:

	Command line interface (text display, keyboard input)
	Window/mouse environment.

OS - High Level

Logical layer.

Manages files, networks, access to the Internet.

OS - Low Level

Hardware or physical layer.

Manages memory, disk drives

More Thoughts

In window-based systems such as Windows 9X/2000/XP and the Macintosh, software programs or applications use the operating system to do everything from storing the program and data to sending information to the printer or display.

In fact, as operating systems have become more robust with the advent of windowing systems, many functions once reserved for the program (e.g., managing the user interface) are now handled by the operating system.

For all intents and purposes, the operating system is very much a part of many of any computer programs!