LEARNING OBJECTIVES
• Differentiate between the two major types of software
• Describe the general functions of the operating system
• Differentiate among types of operating systems and describe each type
• Identify three methods for developing applications software
The Software Crisis
• New software applications cannot be developed fast enough to:
Ø Keep up with dynamic business environment
Ø Keep pace with rapid hardware advances
• Lag in software development limits IS capabilities
Ø The Software Crisis (continued)
• In addition to new application development, existing software must also be maintained (80% IT personnel effort towards maintenance).
• Increasing complexity leads to the increased potential for “bugs.”
• Testing and “debugging” software is expensive and time-consuming.
Software Fundamentals
• Some basic terms…
Ø Computer programs – sequences of instructions for the computer
Ø Stored program concept – instructions written in programs are stored and executed by CPU when needed
Ø Programming – process of writing (or coding) programs
Ø Programmers – individuals who perform programming
Systems Software
Ø Instructions that manage the hardware resources
Application Software
Ø Instructions that perform specific user tasks
System Software
• System software is software that:
Ø Controls and supports the computer system’s activities
Ø Supports application software by directing the computer’s basic functions
Ø Facilitates program development, testing, and debugging
Ø Is independent of any specific type of application
• System Control Programs
Ø Control use of all system resources (hardware, software, data); operating system
• System Support Programs
Ø Specialized support capabilities
System Control Programs
• Operating System – main system control program
Ø supervises the overall operation of the computer
Ø allocates CPU time and main memory to programs running on the computer
Ø provides an interface between the user and the hardware
Operating System Services
• Process management – manage program(s) running on processor
Ø Multitasking or Multiprogramming – managing two or more tasks, or programs, running on the computer system at the same time
Ø Multithreading – type of multitasking; run two or more tasks from the same application simultaneously
Ø Timesharing – many users share same CPU, each using a different input/output terminal
Ø Multiprocessing – simultaneous processing with multiple CPUs
Ø Operating System Services (continued)
• Virtual memory – simulates more main memory than actually exists in the computer system
• File management and security – managing the arrangement of, and access to, files held in secondary storage
• Fault tolerance – system can produce correct results and continue to operate even in the presence of faults or errors
• User interface – allows users to have direct control of visible objects (icons) and actions that replace complex command syntax
Types of Operating Systems
• Departmental Server Operating Systems
Ø Support hundreds of concurrent users
Ø UNIX, Linux, Windows 2000, Windows XP, Novell NetWare
• Enterprise Operating Systems
Ø Support thousands of concurrent users; millions of transactions per day
Ø IBM’s OS/390, IBM’s VM (Virtual Machine), IBM’s VSE (Virtual Storage Extended), and IBM’s OS/400
