FUNDAMENTALS OF COMPUTER HARDWARE


ORGANIZATION OF COMPUTER SYSTEM COMPONENTS

    Now that we've examined what is a computer[1], let's look again at our computer definition: A computer is a fast and accurate symbol manipulating system that is organized to accept, store, and process data and produce output results under the direction of a stored program of instructions. This section explains why a computer is a system and how a computer system is organized.

shows the basic organization of a computer system. Key elements in this system include input, processing, and output devices. Let's examine each component of the system in more detail.

INPUT DEVICES


Computer systems use many devices for input purpose. As shown in Fig.1-2, some INPUT DEVICES allow direct human/machine communication, while some first require data to be recorded on an input medium such as a magnetizable material. Devices that read data magnetically recorded on specially coated plastic tapes or flexible or floppy plastic disks are popular. The keyboard of a workstation connected directly to … or ONLINE to … a computer is an example of a direct input device. Additional direct input devices include the mouse, input pen, touch screen, and microphone. Regardless of the type of device used, all are components for interpretation and communication between people and computer systems.

CENTRAL PROCESSING UNIT.


The heart of any computer system is the central processing unit (CPU). As Fig. 1-3 shows, there are three main sections found in the CPU of a typical personal computer system: The primary storage section, The arithmetic-logic section, and The control section. But these three sections aren't unique to personal computer: They are found in CPUs of all sizes.

OUTPUT DEVICES


Like input units, output devices are instruments of interpretation and communication between humans and computer systems of all sizes. These devices take output results from the CPU in machine-coded form and convert them into a form that can be used (a) by people (e.g. a printed and/or displayed report) or (b) as machine input in another processing cycle.
    In personal computer systems (Fig. 1-3), display screen and desktop printers are popular output devices. Larger and faster printers, many online workstations, and magnetic tape drives are commonly found in larger systems.
    The input/output and secondary storage units shown in Fig. 1-3 are sometimes called peripheral devices (or just peripherals). This terminology refers to the fact that although these devices are not a part of the CPU, they are often located near it.

1 DATA STRUCTURE


A data structure is a data type whose values are composed of component elements that are related by some structure.
    Since a data structure is a data type, it has a set of operations on its values. In addition, there may be operations that act on its component elements.
    The operations of a structured data type might not only act on the values of the data type, they might also act on component elements of the data structure.

The data types arrays and records are native to many programming languages. By using the pointer data type and dynamic memory allocation, many programming languages also provide the facilities for constructing linked structures. Arrays, records, and linked structures provide the building blocks for implementing what we might call higher-level abstractions. The first two higher-level abstract data types that we take up-stacks and queues-are extremely important to computing.

A stack is a data type whose major attributes are determined by the rules governing the insertion and deletion of its elements. The only element that can be deleted or removed is the one that was inserted most recently. Such a structure is said to have a last-in/first-out (LIFO) behavior, or protocol.
    The simplicity of the data type stack belies its importance[1]. Many computer systems have stacks built into their circuitry [2] and have machine-level instructions to operate the hardware stack. The sequencing of calls to and returns from subroutines follows a stack protocol. Arithmetic

expressions are often evaluated by a sequence of operations on a stack. Many handheld calculators use a stack mode of operation. In studying computer science, you can expect to see many examples of stacks.
    Queues occur frequently in everyday life and are therefore familiar to us. The line of people waiting for service at a bank or for tickets at a movie theater and the line of autos at a traffic light are examples of queues. The main feature of queues is that they follow a first-come/first-served rule.

Contrary to a stack, in which the latest element inserted is the first removed or served, in queues the earliest element inserted is the first served. In social settings, the rule appeals to our sense of equality and fairness.
    There are many applications of the first-in/first-out (FIFO) protocol of queues in computing. For example, the line of input/output (I/O) requests waiting for access to a disk drive in a multiuser time-sharing system might be a queue[3]. The line of computing jobs waiting to be run on a computer system might also be a queue. The jobs and I/O requests are serviced in order of their arrival, that is, the first in is the first out.

There is a second kind of queue that is important. An everyday example can be seen in an emergency room of a hospital. In large emergencies it is common to first treat the worst injured patients who are likely to survive. In certain societies in which less emphasis is placed on equality, people with higher social standing may be treated first.

In computer systems, events that demand the attention of the computer are often handled according to a most-important-event/first-served, or highest-priority in/first-out (HPIFO), rule. Such queues are called priority queues, in this type of queue service is not in order of time of arrival but rather in order of some measure of priority.

COMPUTER LANGUAGES


Computer languages have undergone[1] dramatic evolution since the first electronic computers were built to assist in telemetry calculations during World War II. Early on, programmers worked with the most primitive computer instructions: machine language. These instructions were represented by long strings of ones and zeroes. Soon, assemblers were invented to map machine instructions to human-readable and manageable mnemonics[2], such as ADD and MOV.

In time, higher-level languages evolved, such as BASIC and COBOL. These languages let people work with something approximating words and sentences, such as Let I = 100. These instructions were translated back into machine language by interpreters and compilers. An interpreter translates a program as it reads it, turning the program instructions, or code, directly into actions[3]. A compiler translates the code into an intermediary form. This step is called compiling, and produces an object file. The compiler then invokes a linker, which turns the object file into an executable program.

Because interpreters read the code as it is written and execute the code on the spot, interpreters are easy for the programmer to work with. Compilers, however, introduce the extra steps of compiling and linking the code, which is inconvenient. Compilers produce a program that is very fast each time it is run. However, the time-consuming task of translating the source code into machine language has already been accomplished.

Another advantage of many compiled languages like C++ is that you can distribute the executable program to people who don't have the compiler. With an interpretive language, you must have the language to run the program.
    For many years, the principle goal of computer programmers was to write short pieces of code that would execute quickly. The program needed to be small, because memory was expensive, and it needed to be fast, because processing power was also expensive[.

As computers have become smaller, cheaper, and faster, and as the cost of memory has fallen, these priorities have changed. Today the cost of a programmer's time far outweighs the cost of most of the computers in use by businesses[7]. Well-written, easy-to-maintain code is at a premium. Easy- to-maintain means that as business requirements change, the program can be extended and enhanced without great expense.

The problems programmers are asked to solve have been changing. Twenty years ago, programs were created to manage large amounts of raw data. The people writing the code and the people using the program were all computer professionals. Today, computers are in use by far more people, and most know very little about how computers and programs work. Computers are tools used by people who are more interested in solving their business problems than struggling with the computer.

Ironically, in order to become easier to use for this new audience, programs have become far more sophisticated. Gone are the days when users typed in cryptic commands at esoteric prompts, only to see a stream of raw data[8]. Today's programs use sophisticated "user-friendly interfaces," involving multiple windows, menus, dialog boxes with which we've all become familiar. The programs written to support this new approach are far more complex than those written just ten years ago.As programming requirements have changed, both languages and the techniques used for writing programs have evolved.

DBMS AND MIS


You know that a data base is a collection of logically related data elements that may be structured in various ways to meet the multiple processing and retrieval needs of organizations and individuals.
    You'll see in the following pages that complex data relationships and linkages may be found in all but the simplest data bases[1]. The system software package that handles the difficult tasks associated with creating, accessing, and maintaining data base records is called a data base management system (DBMS). The programs in a DBMS package establish an interface between the data base itself and the users of the data base. (These users may be applications programmers, managers and others with information needs, and various OS programs.)

A DBMS can organize, process, and present selected data elements from the data base, and assemble the needed items from the common data base in response to the queries of those who aren't programmers. In a file-oriented system, users needing special information may communicate their needs to a programmer, who, when time permits, will write one or more programs to extract the data and prepare the information[2]. The availability of a DBMS, however, offers users a much faster alternative communications path .

The management information system (MIS) concept has been defined in dozens of ways. Since one organization's model of an MIS is likely to differ from that of another, it's not surprising that their MIS definitions would also vary in scope and breadth. For our purposes, an MIS can be defined as a network of computer-based data processing procedures developed in an organization and integrated as necessary with manual and other procedures for the purpose of providing timely and effective information to support decision making and other necessary management functions.

Although MIS models differ, most of them recognize the concepts shown in Fig.4-2. In addition to what might be termed the horizontal management structure shown in Fig. 4-2(a), an organization is also divided vertically into different specialities and functions which require separate information flows (see Fig. 4-2(b)). Combining the horizontal managerial levels with the vertical specialities produces the complex organizational structure shown in Fig. 4-2(c). Underlying this structure is a data base consisting, ideally, of internally and externally produced data relating to past, present, and predicted future events.

OFFICE AUTOMATION


Office automation is the application of computer and communications technology to improve the productivity of clerical and managerial office workers. In the mid-1950s, the term was used as a synonym for almost any form of data processing, referring to the ways in which[1] bookkeeping tasks were automated. After some years of disuse, the term was revived in the mid-1970s to describe the interactive use of word and text processing systems, which would later be combined with powerful computer tools, thereby leading to a so-called "integrated electronic office of the future".

The major functional components of an office automation system include text processing, electronic mail, information storage and retrieval, personal assistance features, and task management. These may be implemented on various types of hardware and usually include a video display terminal, input devices, and a hard-copy output device for "letter-quality" printing, etc.

Initially, systems sold by major manufacturers were aimed at clerical and secretarial personnel. These were mainly developed to do word processing and record processing (maintenance of small sequential files, such as names and addresses, which are ultimately sorted and merged into letters).
    More recently, attention has also been focused on systems which directly support the principals (managers and professional workers). Such systems emphasize the managerial communications function.

Electronic mail and filing permit a user to compose and transmit a message on an office automation system. In the early 1970s, the ARPANET community developed[2] a number of such systems which have been heavily used. Through standard message format protocols, several hundred different computers and electronic mail interfaces are able to exchange information with one another.

These protocols are like the post office's specification of how recipient and return addresses should appear on envelopes and which sizes are allowable for envelopes. In the electronic message world, they describe what sequences of characters are required at the beginning of a message to identify the sending and receiving mailboxes.

Today's organizations have a wide variety of office automation hardware and software components at their disposal. The list includes telephone and computer systems, electronic mail, word processing, desktop publishing, database management systems, two-way cable TV, office-to-office satellite broadcasting, on-line database services, and voice recognition and synthesis. Each of these components is intended to automate a task or function that is presently performed manually.

But experts agree that the key to attaining office automation lies in integration - incorporating all the components into a whole system such that information can be processed and communicated with maximum technical assistance and minimum human intervention. This goal can be accomplished when (1) computer, communication, and office equipment are networked and (2) an office worker can easily access the entire system through a personal computer sitting on his or her desk. Then it will be possible to change substantially the way people work in an office.