Computer hardware is virtually useless without computer software. Software is the programs that are needed to accomplish the input, processing, output, storage, and control activities of information systems.
Computer software is typically classified into two major types of programs: system software and application software.
Systems software are programs that manage the resources of the computer system and simplify applications programming. They include software such as the operating system, database management systems, networking software, translators, and software utilities.
Application software are programs that direct the performance of a particular use, or application, of computers to meet the information processing needs of end users. They include Aoff-the-shelf@ software such as word processing and spreadsheet packages, as well as internally or externally developed software that is designed to meet the specific needs of an organization.
Software trends have been away from custom-designed one-of-kind programs developed by the professional programmers or end users of an organization toward the use of Aoff-the-shelf@ software packages acquired by end users from software vendors.
Two types of packages are available:
1. Vertical packages - assist users within a specific industry segment. Examples include packages that help to manage construction projects, keep track of inventory of hospitals, or fast-food outlets.
2. Horizontal packages - can perform a certain general function, such as accounting, or office automation, for a range of businesses.
Relationships between Hardware and Software Components [Figure 5.1][Slide 5-3]
Figure 5.1 is an excellent tool to use to explain the relationship that exists between computer systems hardware, systems software, and application software. This Aonion-skin@ model indicates that the outer layers rely on the facilities furnished by the inner ones.
5.2 Operating Systems
The most important system software package for any computer is its operating system. Every computer system runs under the control of an operating system. Operating systems for computers that are shared by many users are considerably more complex than operating systems for personal computers.
What Does an Operating System Do?
The operating system is the software that controls all the resources of a computer system. For example it:
1. Assigns the needed hardware to programs
2. Schedules programs for execution on the processor
3. Allocates the memory required for each program
4. Assigns the necessary input and output devices
5. Manages the data and program files stored in secondary storage
6. Maintains file directories and provides access to the data in the files
7. Interacts with the users
Multiprogramming is the capacity of a computer to executing several programs concurrently on the same processor by having one of the programs using the processor while others are performing input or output.
Multiprogramming requires that the active parts of the programs competing for the processor be available in main memory. Virtual memory is the seemingly expanded capacity of the main memory of the computer, and achieved by keeping in the main memory only the immediately needed parts of programs, with the complete programs kept in secondary storage.
Modes of Computer System Operation
Operating systems enable the system they manage to operate in various modes. These include batch processing, time sharing, and real-time processing.
Batch processing Processing programs or transactions in batches, without a user's interaction.
Time Sharing Systems providing interactive processing by allocating a short time slice for the use of the server to each user in turn.
Real-time Processing Systems that respond to an event within a fixed time interval; used for example, in manufacturing plants or to collect data from several pieces of equipment in a laboratory.
With the move toward multiprocessors, in which several (or even many) processors are configured in a single computer system, multiprocessing operating systems have been designed to allocate the work to the multiple processors. These systems also support multiprogramming, which allows many programs to compete for the processors.
Operating Systems for Personal Computers
The operating systems of personal computers which are dedicated to a single user are vastly simpler than the operating systems running larger machines, to which hundreds or thousands of users may have simultaneous access. One important capability an operating system can offer in a personal computing environment is multitasking: the ability to run several tasks at once on behalf of a user.
The most popular microcomputer operating systems are:
Windows 95 - Windows 95 is an advanced operating system
- graphical user interface
- true multitasking
- network capabilities
DOS - is an older operating system which was used on microcomputers
- is a single user, single-tasking operating system
- can add a GUI interface and multitasking capabilities by using an operating environment such as Microsoft Windows
OS/2 Warp - graphical user interface
- virtual memory capabilities
- telecommunications capabilities
Windows NT - multitasking network operating system
- multiuser network operating system
- installed on network servers to manage local area networks with high-performance computing requirements
UNIX - popular operating system that is available for micros, minis, and mainframe computer systems
- multitasking and multiuser system
- installs on network servers
MacIntosh System 7 - multitasking
- virtual memory capabilities
- graphical user interface
A user interface is a combination of means by which a user interacts with the computer system. It allows the end user to communicate with the operating system so they can load programs, access files, and accomplish other tasks. The three main types of user interfaces are:
1. Command drive
2. Menu drive
3. Graphical User Interface (GUI)
The most popular graphical user interface is that provided by Windows 95. The Windows environment has become a standard platform for computers.
The Goal of Open Systems
A drive is to use open systems in organizational computing, so that the software and hardware of any vendor can operate with those of any other, calls for an operating system that would run on any hardware platform. The term Aopen system@ is used as the opposite of proprietary systems of a specific manufacturer.
In open systems, organizations want portability, scalability, and interoperability of applications software.
Portable application: can be moved from one computer system to another.
Scalable application: is one that can be moved without significant reprogramming.
Interoperability: means that machines of various vendors and capabilities can work together to produce needed information.