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Mahesh - RSREC INTRODUCTION TO COMPUTERS TRENDS IN COMPUTER SYSTEMS Today’ s comput er syste ms come in a var iet y of siz es, sha pes , and comput ing capabi li tie s. Rapid hardware and software developments and changing end user needs continue to drive the emergence of new mod els of comput ers , from the smallest hand-held per sonal digital assistant for end use rs, to the lar ges t multiple-CPU mainframe for the enterprise. Categories such as mainframes, midrange computers, and microcomputers are still used to help us express the relative processing power and number of end users that can be supported by different types of computers. In addition, experts continue to predict the merging or disappearance of several computer categories. They feel, for example, that many midrange and mainframe systems have been made obsolete by the power and versatility of client/server networks of end user microcomputers and servers. COMPUTER GENERATIONS It is important to realize that major changes and trends in computer systems have occurred during the major stages-or generations-of computing, and will continue into the future. The first generation of computers developed in the early 1950s, the second generation blossomed during the late 1960s, the third generation took computing into the 1970s, and the fourth generation has been the computer technology of the 1980s and 1990s. A fifth generation of computers that accelerates the trends of the previous generations is expected to evolve as we enter the 21st century. Notice that computers continue to become smaller, faster, more reliable, less costly to purchase and maintain, and more interconnected within computer networks. First-generation computing involved massive computers using hundreds or thousands of vacuum tubes for their proces sing and memory circu itry. These large computers generated enormous amounts of heat; their vacuum tubes had to be replaced frequently. Thus, they had large electrical power, air conditioning, and maint enance requi remen ts. Firs t-gene rati on comput ers had main memories of only a few thous and charact ers and millisecond processing speeds. They used magnetic drums or tape for secondary storage and punched cards or paper tape as input and output media. Second-generation comput ing used transist ors and other solid-st ate, semic onduct or device s that were wired to circuit boards in the computers. Transistorized circuits were much smaller and much more reliable, generated little heat, were less expensive, and required less power than vacuum tubes. Tiny magnetic cores were used for the computer’s memory, or internal storage. Many second-generation computers had main memory capacities of less than 100 kilobytes and microsecond processing, speeds. Removable magnetic disk packs were introduced, and magnetic tape merged as the major input, output, and secondary storage medium for large computer installations. Third-generation computing saw the development of computers that used integrated circuits, in which thousands of transistors and other circuit elements are etched on tiny chips of silicon. Main memory capacities increased to several megabytes and processing speeds jumped to millions of instructions per second (MIPS) as telecommunications capabilities became common. This made it possible for operating system programs to come into widespread use that automated and supervised the activities of many types of peripheral devices and processing by mainframe computers of several programs at the same time, frequently involving networks of users at remote terminals. Integrated circuit technology also made possible the development and widespread use of small computers called minicomputers in the third computer generation. Fourth-generation computing relies on the use of LSI (large-scale integration) and VLSI (very-large- scale integration) technologies that cram hundreds of thousands or millions of transistors and other circuit elements on each chip. This en abled the development of microprocessors, in which all of the circuits of a CP are contai ned on a single chi p wit h proces sing speeds of mil lions of ins tru ctions per second. Mai n memory capacities ranging from a few megabytes to several gigabytes can also be achieved by memory chips that replaced magnetic core memories. Microcomputers, which use microprocessor CPUs and a variety of peripheral 1
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Mahesh - RSREC
During and after the implementation process, the program being developed must be checked to ensure that itneeds its specification and delivers the functionality expected by the people paying for the software.Verification and validation is the name given to these checking and analysis processes. Verification andvalidation starts with requirements reviews and continues through design reviews and code inspections to
product testing.Verification and validation is not the same thing; although they are often confused.Boehm expressed the difference between them:
Verification: Are we building the product right?Validation: Are we building the right product?These definitions tell us that the role of verification involves checking that the software confirms to itsspecifications. One should check that it meets its specified functional and non functional requirements.Validation, however, is a more general process. The aim of validation is to ensure that the software systemmeets the customer’s expectations. It goes beyond checking that system confirms to its specifications toshowing that the software does what customer expects it to do.The ultimate goal of the verification and validation process is to establish confidence that the software system is‘fit for purpose’.The level of required confidence depends up on following factors:1. Software function: The level of confidence required depends on how critical the software is to an
organization.2. User expectations: Since from 1990’s the users have high expectations of their software. They are not willingto accept the system failures. So, software companies must devote more effort to verification and validation.3. Marketing environment: When a system is marketed, the sellers of the system must take into accountcompeting programs, the price those customers are willing to pay for a system and the required schedule for delivering that system. Where a company has few competitors, it may decide to release a program before it has
been fully tested and debugged because they want to be first in the market. When the customers are not willingto pay high prices for software, they may be willing to tolerate more software faults. All of these factors must beconsidered when deciding how much effort should be spent on verification and validation.With in verification and validation process there are two complementary approaches to system checking andanalysis:1. Software inspections or peer reviews: In this process the person will analyze and check systemrepresentations such as the requirements document, design diagrams and the program source code. They can useinspections at all stages of the process. Software inspections and automated analysis are static verification andvalidation techniques as it don’t need to run the software on a computer.2. Software testing: Software testing involves running an implementation of the software with test data. Itexamines the outputs of the software and its operational behavior to check that it is performing as required.Testing is a dynamic technique of verification and validation.
Inspection Process
