Fundamentals

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Fundamentals
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Main Hardware Components

• Central Processing Unit (CPU)
• Main Memory (random access memory or RAM)
• Auxiliary Storage
• Input Devices
• Output Devices

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CPU

• Performs arithmetic and comparisons
• The real brain of the computer

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RAM

• Temporarily stores any program being executed on
  the computer, as well as the data on which the
  program operates

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Auxiliary Storage

• Provides a place where data can be permanently
  stored and then transferred to and from main
  memory.
• Examples floppy disk, hard disk, CD-ROM, Zip
  drives, tape backup

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Input Devices

• Accept data from an external source and convert
  it to electrical signals, which are sent to the
  CPU.
• Examples keyboard, mouse, joystick, scanner,
  microphone
• Technically, auxiliary storage is also considered
  an input device

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Output Devices

• Accept electrical signals from the CPU and
  convert them to a form suitable for output.
• Examples monitor, printer, speakers
• Technically, auxiliary storage is also considered
  an output device.

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Bits and Bytes How Data is Represented in the
Computer

• All computer calculations are done using binary
  arithmetic, which uses only 0s and 1s. Each
  binary digit (0 or 1) is called a bit.
• This is convenient for the computer hardware
  because in any circuit, 0 might be represented by
  a low voltage signal and 1 might be represented
  by a higher voltage signal. I.e., its easy for
  the electronics to distinguish between just two
  possible values.

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• But much of the data we use on the computer isnt
  really numerical.
• How does the computer represent things like
  alphabetic data, or pictures, for example?
• Answer It still uses bits.

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Bytes

• Computer storage is arranged into bytes, where
  each byte is just a group of 8 bits.
• A byte is considered the smallest addressable
  unit of memory, and measurements of memory size
  or disk capacity are always expressed in terms of
  bytes.
• Bytes are also convenient for representing
  alphabetic data.

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• An 8-bit byte can contain any of 28 256
  different combinations of 0s and 1s, like
  00000000, or 01101001, or 11111111, for example.
• Alphabetic characters are represented in the
  computer, one byte per character, using ASCII
  codes.

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ASCII Codes

• A 01000001
• B 01000010
• C 01000011
• D 01000100
• Etc.

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• The codes for the lower-case letters are
  different, and there are distinct codes for all
  the other standard characters appearing on the
  keyboard, including punctuation marks, the space,
  the carriage return, and the 10 digits. But each
  of these fits into a single byte.

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Everything is stored as bytes

• Other kinds of data are also ultimately stored as
  bytes, using some kind of coded representation.
• For example, a single digital image can be
  represented by specifying what appears (color,
  intensity, etc.) in each separate pixel (picture
  element) of the image.

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• Because there are potentially a very large number
  of pixels in a high-quality image, it may take
  many bytes to represent this image.
• And, of course, if this is a changing video
  image, the number of bytes to represent it will
  be much larger still.

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Data Compression

• One thing that helps reduce the number of bytes
  required is the use of data compression.
• An example of a data compression program is
  WinZip.
• Another type of data compression is used in .jpg
  images.

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How does data compression work?

• To give a simple-minded example, suppose that we
  wanted to store (or transmit) a sequence of 100
  bytes, all of which were identical (say ASCII for
  the character A).
• Instead of using 100 bytes for this, we could use
  2 bytes, one representing the number 100 (which
  is 01100100 in binary) and the other representing
  the ASCII code for A.
• Thus in this case weve compressed 100 bytes down
  to 2.

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• The general idea behind data compression is to be
  able to find patterns in the original data which
  can be encoded in a shorter way.
• Uncompressing the data then just requires
  regenerating the original data from this shorter
  pattern description.

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Programs are in bytes too

• Also represented as bytes in the computer are the
  instructions that make up the executable programs
  that the CPU runs.

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• Thus everything in the computer, programs or
  data, is ultimately just bytes (or bits), as far
  as the internal workings go at the lowest levels
  of the electronics.
• Fortunately for us, though, as computer users, or
  even as computer programmers, we dont have to
  interact with the computer at this level.

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CPU

• The standard personal computer (PC) has a
  single-chip CPU, also called a microprocessor.
• Examples of microprocessors found in standard PCs
  are Intels Pentium, Pentium II, Pentium III, and
  Celeron.
• Other manufacturers making Intel-compatible
  microprocessors are AMD and Cyrix.

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• Microprocessor speed is typically expressed in
  terms of the number of clock cycles per second,
  a rough measure of the number of program
  instructions that can be carried out in each
  second.
• One clock cycle per second would be 1 hertz (Hz).
  

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• Actual speeds of current top-end PC
  microprocessors range from roughly 250-500
  megahertz (MHz), which means 250 million to 500
  million clock cycles per second.
• The higher this number, the faster the processor.

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Standard Prefixes Used to Express Various
Computer-Related Quantities

• Kilo means 103 or 1,000
• Mega means 106 or 1,000,000
• Giga means 109 or 1,000,000,000
• Tera means 1012 or 1,000,000,000,000
• Milli means 10-3 or 0.001
• Micro means 10-6 or 0.000001
• Nano means 10-9 or 0.000000001

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Main Memory (RAM)

• Called random access because any particular
  memory location in it is as fast to retrieve data
  from or store data in as any other.
• Furthermore the time it takes is very short, less
  than 1 millisecond, so accessing data in main
  memory is very fast.

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• But the data stored in it only lasts as long as
  there is power being supplied to the computer.
• Typical PCs have 32 or 64 megabytes (MB) of RAM.
  The more RAM, the faster the computer will seem
  to run because there is less time spent storing
  or retrieving the data on disk, which is much
  slower.

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Hard Disk

• Stores data on spinning magnetic platters in a
  sealed enclosure.
• Typical capacity of a hard disk on a PC is 1 or
  more gigabytes (GB).
• Typical access time for a hard disk is on the
  order of 10 milliseconds, on average, which is
  much slower than the access time for main memory.

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Floppy Disk

• Made of flexible plastic coated with magnetic
  material, and enclosed in a hard plastic case.
• Its capacity is 1.44 MB, and its average access
  time is around 175 milliseconds.

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Other Auxiliary Storage Devices

• CD-ROM (Compact Disk, Read-Only Memory)
• DVD (Digital Versatile Disk, or originally
  Digital Video Disk)
• Zip Drive
• Tape Backup Unit

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Input Devices

• Keyboard
• Mouse
• Microphone
• Scanner
• Digital Camera
• Joystick

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Output Devices

• Monitor
• CRT (cathode ray tube)
• LCD (liquid crystal display)
• Printer
• Inkjet
• Laser
• Speaker

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Software

• System Software (Operating System)
• Application Software

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System Software

• Main function is to maintain the file system and
  also to allow application programs to have access
  to computer input (from the keyboard or mouse,
  for example) and to create computer output (to
  the monitor, for example).
• Provides an interface between application
  programs and the hardware itself.

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Files and Folders

• A file is a collection of bytes on the disk that
  represents a program or data for use by a
  program.
• Files are organized hierarchically, in a tree
  structure. Files that contain other files are
  called folders in Windows 95/98 and directories
  in older operating systems like DOS and Unix.

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Application Programs

• Application programs represent all other software
  that can be run on the computer, to allow the
  user to do such varied tasks as word processing,
  playing games, sending email, and browsing the
  World Wide Web, for example.
• These programs are typically obtained from
  vendors but application programs can also be
  created by sophisticated users.

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• Specific application programs we will use in this
  course are
• Internet Explorer (for web browsing)
• Word (for word processing)
• Excel (for spreadsheet manipulation)
• Access (for database manipulation)
• PowerPoint (for creating and showing
  presentations)