Exploring Computers

Hardware and Software

    Computers are made up of hardware and software.  Hardware is the tangible, physical equipment that can be seen and touched.  Examples of hardware are things such as the keyboard, printer, monitor, and computer chips.

    Software is the intangible instructions that tell the computer what to do.  Software are things such as Carmen SanDiego, KidPix, ClarisWorks, or Oregon Trail.  People who write software (instructions that tell the computer what to do) are called programmers.

    Programmers write instructions, or programs, to the computer so that it is able to execute a task or operate properly.  A program can be defined as a series of detailed step-by-step instructions that tell the computer precisely what actions to perform.

    Many people believe that computers can do just about anything and that their level of sophistication requires a genius to program and run them.  In reality, computers are very simple devices that can perform only four basic functions.  A computer can (1) store data and programs, (2) function unattended due to its ability to interpret and follow instructions it is provided, (3) do arithmetic calculations, and (4) perform logical comparisons.  What makes the computer such a powerful device, given only these four basic functions, is its tremendous speed, its accuracy, and its ability to store vast volumes of data.

Memory

    The computer must be given instructions, in the form of software, which tell it exactly what to do.  The instructions that the computer follows are stored in locations known as memory.  For simplicity purposes think of memory in two categories:
(1) The computer's Internal memory  (ex. microchips)
(2) The computer's External memory  (ex. diskettes & hard drives)

    The computer's Internal memory which is composed of computer chips is divided into two types:  RAM (random-access memory) and ROM (read-only memory).  RAM's primary purpose is to temporarily store programs given to it by a programmer or operator of the computer.  This type of memory is temporary because it is erased when the computer is turned off (powered down).  In other words, all the information in RAM is erased when the computer is turned off.  It is called random access because  the processor can jump directly form one location to another in random order as the program is needed.  RAM holds programs such as  KidPix, ClarisWorks, Oregon Trail or whatever program the computer is operating under.

    ROM's primary purpose is to store important instructions that the computer will reuse over and over such as what to do when the computer is turned on and how to control specific requests made by the computer.  ROM is permanent memory that can not be changed or erased.  This is why it is called Read-Only Memory.

Input and Output devices

    A hardware device which enables the computer to accept data is called an input device.  The most common example of an input device is a keyboard.  Other commonly known input devices include a joystick, mouse, bar-code scanner, light pen, touch display screen, speech recognition device, and graphic tablet.

    A hardware device which reports the information in a form we can understand is called an output device.  The two most common forms of output devices are monitor, and printer.  Other examples include sound or music synthesizers, speech synthesizers, real-time controllers, and robots.
Questions

Processors
    All computers do processing by following a series of instructions in a software program.  The computer chip that receives and carries out these instructions is called the processor.  All computer systems, regardless of size or manufacturer, have processors (also referred to as central processing units or CPUs).

    The processor performs many different functions.  It receives and temporarily stores instructions as well as the data to be processed.  It moves and changes stored data.  It does arithmetic calculations.  It makes decisions of logic, such as determining if two numbers are equal.  It directs the action of the input and output devices.   The CPU is often referred to as the brains of the computer system.

External or Auxiliary Storage

    Nearly all general-purpose computers include the ability to connect to additional storage devices that hold data outside the memory of the computer.  These additional storage devices are known as external or auxiliary storage.  External  storage devices are on-line to the computer; that is, they are connected directly to the computer.  They are, therefore, under the control of the processor and can be used at all times.  The most common form of external storage is a disk drive.    Other forms of external storage include hard drives and CD- ROM drives.

    The disk drive records data in a method similar to that used by a cassette tape recorder.  The information is actually magnetically encoded into the floppy disk.  External storage is used to hold computer programs so they may be read into the computer's random-access memory (RAM) when they are needed.  Large amounts of data may also be stored on external storage.  Remember from an earlier section that data is stored in RAM temporary.  Therefore, any data that is needed to be kept for future use is usually recorded on a magnetic disk before the computer is powered down.

MicroChips

    Scientists in the United States and Japan are trying to overcome the physical limits of chip design technology that began less than three decades ago.  Each country is rushing to be the first to develop microcomputer chips that contain one billion transistors.

    Transistor technology preceded chip technology.  Transistors were smaller, more efficient, and more reliable than their predecessors the vacuum tubes.  The major limitation of transistors was in their limited number of interconnections.  In other words, because of the sophisticated circuitry of computers, an enormous number of connections between transistors was required.  Unlike the number of transistor connections needed in a radio, the number of transistor connections in computers extends into the millions.  Chip technology solved the interconnections problem by placing several transistors on a tiny silicon surface.  Thus, computer power and storage capabilities expanded dramatically.

    The number of transistors which can be placed on a chip has increased from fewer than ten in  the early chips to thousands in the chips used today.  Chip technology has enabled the chip's capacity to double every year since its creation until just a few years ago.  However, today's chip designers have run into a problem concerning the physical limitations of a single chip; therefore, the interconnections problem of the transistor technology has resurfaced.

The Computer's World

    To help you understand how the computer works, imagine that each character is represented inside the computer by a series of electronic switches.  In many ways, these electronic switches can be compared to the light switches in our home.  A light switch can be in only one of two states: on or off.  The circuits inside the computer can be thought of in much the same way as the light switches.  The electronic switches can be either on or off.  Since on and off represent only two conditions, it is impossible to directly store numbers or  letters.  Instead, they are converted into binary numbers.  Binary means "consisting of two things", so a binary number is made by using only two digits, 0 and 1.  Our and much of the world's number system is based on the 10 system but the computer's system is based on the Binary system.  Therefore the binary number system is the only coding system the computer actually understands.

    Imagine eight on/off switches grouped inside the computer.  It takes eight switches (Bits) to store one character (letter, symbol, or space).  As shown below 01010011 is the way the computer understands the letter S.  A combination of eight switches (bits)  is called a byte in computer terminology.  The computer groups eight bits together to form a byte because it has proven to be a good combination for the computer to handle.

      0      1       0       1      0       0       1      1                S

    By using eight bits to turn various switches on and off, there are 256 different combinations possible.  In the binary number system, there can be as many 0's and 1's as needed within the eight switches to represent a particular number.  Each 0 can be thought of as representing a switch that is turned off, while each 1 represents a switch that is turned on.

    Each time a key on a keyboard is struck, a binary number is generated in the computer via electronic signaling (see example above).  Inside the computer, the binary number is stored in a memory chip.  All data inside the computer is represented by the use of binary numbers.

    We have now learned that the processor and memory (both ROM and RAM) are made up of electronic circuits that represent information by turning switches off and on.  And we learned that eight switches or bits make up a byte and each byte can store one character of data.

    If we were to key in the name Ernest Grover, it would take thirteen (13) bytes to store the name in RAM.  The space between the first and last name would require one byte, and the  (12) twelve letters of the name would require twelve bytes.
 

    E     r       n        e      s       t                G       r       o       v      e        r    =13 bytes-used
 

    Computer manufacturers express the capacity of memory in terms of the letter K. K is short for Kilobyte, which means 1024 bytes of computer memory.  Many times you hear a computer owner say his or her computer has 64K of memory.  This means that the computer has approximately 64,000 bytes of memory and has the capacity to store up to 64,000 characters during processing in RAM.  Many disks, hard drives, and CDs can store hundreds, thousands, and even millions more memory than the RAM chips in a computer.  For example an average floppy disk can hold 800K or 800,000 bytes; and an average hard drive can hold 40MB which is 40,000,000 bytes and a CD hold up to 500MB of information.  If a MB (megabyte) is 1 million bytes then 1 GB (gigabyte) is 1000 million bytes.  That's more bites than a mosquito does in a lifetime.