Computer Literacy On-Line: Learning Unit 4
John von Neumann Invents the Invisible
John von Neumann, one of the greatest mathematicians of the 20th century, became technical advisor to J. Presper Eckert and John Mauchly, who were searching for an alternative to the plug boards and patch cords used to program ENIAC. In 1945 he wrote the first draft of a paper that drew on their ideas. The paper called for storing the computer's program instructions with the data in memory. Every computer created since has been based on the stored-program concept described in that paper.
Software fills the communication gap between humans with problems to solve and computers that can only understand zeros and ones.
The three major categories of software are:
A Fast, Stupid Machine
Although computers are commonly called "smart machines" or "intelligent machines," a typical computer is capable of doing only the most basic arithmetic operations and a few simple logical comparisons. Computers seem smart because they can perform these operations and comparisons quickly and accurately.
An algorithm is a set of step-by-step procedures for accomplishing a task. A computer program generally starts as an algorithm written in English or some other human language. A programmer's job is to turn the algorithm into a program by adding details, hammering out rough spots, testing procedures, and correcting errors.
The Language of Computers
Every computer processes instructions in a native machine language. Machine language uses numeric codes to represent the most basic computer operations&endash;adding numbers, subtracting numbers, comparing numbers, moving numbers, repeating instructions, and so on.
Today most programmers use programming languages like BASIC and C that fall somewhere between natural human languages and precise machine languages. For a computer to understand a program written in one of these languages, it must use a compiler or other translator program to convert the English-like instructions to the zeros and ones of machine language.
As translators become more sophisticated, programmers can communicate in computer languages that more closely resemble natural languages&endash;the languages people speak and write every day.
Most tasks that required programming two decades ago can now be accomplished with easy-to-use software applications&endash;tools like word processors, spreadsheets, and graphics programs.
Software applications allow users to control computers without thinking like programmers.
The computer applications explored in this book are:
The differences between buying computer software and music software (CDs or cassettes) are:
Not all software is copyrighted and sold through commercial channels. Electronic bulletin boards, the Internet, user groups, and other sources commonly offer public domain software (free for the taking) and shareware (free for the trying, with a send-payment-if-you-keep-it honor system).
In general, most successful software products share two important characteristics.
Integrated Applications and Suites: Multipurpose Software
While most software packages specialize in a particular application&endash;word processing, graphics, or whatever&endash;integrated software packages include several applications designed to work well together and generally include at least these five application types:
The parts of an integrated package may not have all the features of their separately packaged counterparts, but integrated packages still offer several advantages:
Many software companies offer application suites (or office suites )&endash;bundles containing several application programs that are also sold as separate programs. The price of a suite is generally less than the total price of individual applications purchased separately, but more than the cost of an integrated package. Suites generally have more features than integrated programs, but also make greater demands on system memory, disk storage, the CPU, and the user who must learn many extra commands and options.
Vertical-Market and Custom Software
Applications designed specifically for a particular business or industry are sometimes called vertical-market applications. Vertical-market applications tend to cost far more than mass-market applications, because companies that develop the software have very few potential customers through which to recover their development costs. In fact, some custom applications are programmed specifically for single clients.
Software takes care of many messy details of computing for you. These details, and hundreds of others, are handled behind the scenes by system software, a class of software that includes the operating system and utility programs. (By some definitions, system software also includes translator programs.)
What the Operating System Does
Virtually all general-purpose computers today depend on an operating system (OS) to keep hardware running efficiently and to make the process of communication with that hardware easier.
The operating system, as the name implies, is a system of programs that perform a variety of functions, including:
Utility programs serve as tools for doing system maintenance and some repairs that aren't automatically handled by the operating system.
Where the Operating System Lives
Some computers&endash;mostly game machines and special-purpose computers&endash;store their operating systems permanently in ROM (read-only memory) so they are ready to go to work as soon as they are turned on. But because ROM is unchangeable, these machines can't have their operating systems modified or upgraded without hardware transplants.
Most computers include only part of the operating system in ROM&endash;the remainder of the operating system is loaded into memory in a process called booting.
As software evolves, so does the user interface&endash;the look and feel of the computing experience from a human point of view.
Some popular user interfaces are:
A Character-based User Interface: MS-DOS
MS-DOS (Microsoft Disk Operating System, sometimes called just DOS) was the most widely used general-purpose operating system in the world.
IBM chose PC-DOS&endash;the IBM brand of MS-DOS&endash;as the operating system for its first personal computer in 1981.
MS-DOS was designed with a character-based interface&endash;a user interface based on characters rather than graphics.
With a command-line interface, the user types commands and the computer responds to the commands.
It's most common for applications to have a menu-driven interface that allows users to choose commands from on-screen lists called menus.
Graphical User Interfaces: Macintosh and Windows
The Macintosh operating system sports a graphical user interface (sometimes abbreviated GUI, pronounced "gooey") that determines what the user wants by monitoring movements of the mouse. With the mouse the user points to pictures, known as icons, that represents files, folders (collections of files), and disks.
Documents are displayed in windows&endash;framed areas that can be opened, closed, and rearranged with the mouse.
The user selects commands from pull-down menus at the top of the screen.
When you turn on the Macintosh, you see a visual representation of a desktop with a menu bar at the top. An open window shows the contents of the hard disk.
Each icon in the window represents a file or a folder containing other files.
The operating system displays dialog boxes when two-way communication is called for.
Working with a Macintosh is a very different experience from working with an IBM-compatible computer running MS-DOS. But the difference has less to do with the platform&endash;the hardware on which the software runs&endash;than with the software itself.
Microsoft Windows was originally a type of program, known as a shell, that put a Macintosh-like face on MS-DOS. Modern versions of Windows have evolved into complete operating systems and have come to dominate the operating systems market.
Why WIMP Won
Graphical user interfaces with windows, icons, menus, and pointing devices (sometimes called WIMP) offer several clear advantages from the user's point of view:
Graphical user interfaces and friendly operating systems generally require more expensive graphic display systems, more memory, more disk space, and faster processors to work efficiently.
The computer industry is rallying behind graphical user interfaces.
Most personal computers today are built on one of two hardware platforms: the Intel-based platform used by IBM-compatible PCs and the Motorola-based Macintosh platform.
Besides the Macintosh and Windows 9x operating systems, others available today include:
Tomorrow's User Interfaces
Here are some likely candidates for future user interfaces:
Rules of Thumb: The Concise Computer Consumer's Guide
Nine criteria to consider if and when you decide to buy a computer are:
algorithm, application suite (office suite) , booting , bug, character-based interface
command-line interface, compatability, compiler, concurrent processing, copy-protected software
copyrighted software, desktop, dialog box, directory, documentation, emulation, graphical user interface (GUI)
integrated software, machine language, MS-DOS, multitasking, platform, prompt, public domain software
shareware, shell, system software, user interface, virtual reality
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