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Chapter 2
Sections 2.8-2.10
By Gerardo Galvan
RAM and Short Term Memory(STM)
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Primary memory - Short-Term Memory - Volatile.
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Random Access Memory (RAM) – Active information is held in random
access memory.
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Volatile- Content lost when power is turned off.
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Non-volatile – Retains it’s contents with aid of battery.
Flash Memory - A form of silicon memory that sits between fixed content
ROM (read-only memory) chips and normal RAM. Slow to access but will
retain information without need of power.
Disks and Long Term Memory (LTM)
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Secondary memory – Non-volatile
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Disks
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Magnetic – Hard drives, floppy disks…
 Coated with magnetic material on which information is stored.
 Two types of access times: One to locate track and the second to read track.
Optical – Use laser light to read and sometimes write on disk.
 CD-ROM,
 Capacity of around 650 megabytes, but cannot be written to at all.
 Recordable CDs
 A form of WORM device (write-once read-many)
 Rewritable optical disks
 Rewritable time slower than readable time. Primary for archival and not dynamic storage.
Speed and capacity
Compression
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Compression algorithms are used to reduce text, pictures and video file size
by taking advantage of redundancy.
Fractural compression - Good for textured features.
Decompression of image can be from very rough soft-focus to
more detailed than the original.
Storage format and standards
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Common data types: text, images, video and audio.
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ASCII (American standard code for information interchange) – Basic
standard for text storage.
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Assigns character 7 bit code (decimal values 0-27).
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Line-drawing characters, mathematical symbols and international letters (decimal value 128-255)
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UNICODE – 16 bit extension used for larger range of characters such as Japanese Kanji character set.
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Standard generalized markup language (SXML) - used to store structured text in a reasonably extensible way.
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Extensive Markup Language (XML) – Lightweight version of SXML used for web applications.
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RTF – Rich text format. Encodes formatting information including style sheets. Concentrates on appearance.
Methods of access
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Standard database access – Special key fields with an associated index. User
needs to know the key in order to obtain the information.
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Soundex – A way of indexing words. Helps find words which sound similar.
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Forgiving Systems – Helps accommodate users mistakes by providing
suggestions. Do What I Mean (DWIM)
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Free text retrieval systems –Centered on unformatted and unstructured
text. An index of every word in every document.
Moore’s law
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1965 Gordon Moore, co-founder of Intel.
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Number of transistors in a processor doubles every 18 years.
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Computer memory - Doubling magnetic storage approximately every year.
Effects of finite processor speed
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Processing speed can cause faults if it’s too slow or too fast.
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Functional fault - program does the wrong thing.
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Buffers- Remembers key presses, mouse buttons and movements. Typically
used if feedback is too slow, leading to strange effects at the interface.
Limitations on interactive performance
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Computation bound
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The system should be designed so that long delays are not in the middle of interaction and so that the
user gets some idea of how the job is progressing.
Storage Channel bound
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Speed of memory access can interfere with interactive performance.
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Graphics bound
 Special-purpose graphics card to handle common graphics operations.
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Network Capacity
 Speed of the network rather than that of the memory which limits performance.
Networked computing
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Networked computers
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Linked together in networks to increased computing power and memory.
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Disadvantage – slow response time due to multiple users accessing single central
machine, server down, lack of feedback.
Internet
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1969 DARPANET when the US Government’s Department of Defense
commissioned research into networking. 4 mainframes.
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ARPANET – In 1971 renamed from DARPANET TO ARPANET. 23 mainframes.
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Set of common languages(Protocols)
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Transmission Control Protocol (TCP) moves data from A to B.
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Internet Protocol (IP) specifies which B is being referred to so that data goes to
correct place.
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TCP/IP
2.10 Chapter 2 Summary
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Input Devices – Main functions: text and pointing.
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Text Input devices: QWERTY Keyboard, chord keyboards, telephone keypad,
speech input.
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Pointing devices: mouse, touchpad, trackball and joystick.
Screen Output devices
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CRT and LCD screens.
Virtual reality and 3D spaces
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Dataglove, body tracking, head mounted displays and cave environments.
2.10 Chapter 2 Summary
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Printers – ink-jet, bubble-jet and laser printers, dot-matrix and thermal printers.
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Scanners – convert printed images and documents into electronic form.
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RAM – STM and LTM stored on optical and magnetic drives.
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Access information - Multiple indices, free text databases, DWIM (do what I mean)
and Soundex.
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Processing speed is limited by various factors: computation, memory access,
graphics and network delays.