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Chapter 2

Chapter 2. Sections 2.8- 2.10 By Gerardo Galvan. RAM and Short Term Memory(STM). Primary memory - Short-Term Memory - Volatile . Random Access Memory (RAM) – Active information is held in random access memory. Volatile- Content lost when power is turned off.

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Chapter 2

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  1. Chapter 2 Sections 2.8-2.10 By Gerardo Galvan

  2. RAM and Short Term Memory(STM) • Primary memory - Short-Term Memory - Volatile. • Random Access Memory (RAM) – Active information is held in random access memory. • Volatile- Content lost when power is turned off. • 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.

  3. Disks and Long Term Memory (LTM) • Secondary memory – Non-volatile • Disks • 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.

  4. Speed and capacity

  5. Compression • 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.

  6. Storage format and standards • Common data types: text, images, video and audio. • ASCII (American standard code for information interchange) – Basic standard for text storage. • Assigns character 7 bit code (decimal values 0-27). • Line-drawing characters, mathematical symbols and international letters (decimal value 128-255) • UNICODE – 16 bit extension used for larger range of characters such as Japanese Kanji character set. • RTF – Rich text format. Encodes formatting information including style sheets. Concentrates on appearance. • Standard generalized markup language (SXML) - used to store structured text in a reasonably extensible way. • Extensive Markup Language (XML) – Lightweight version of SXML used for web applications.

  7. Methods of access • Standard database access – special key fields with an associated index. Ex. customer number, last order number. • Soundex – Another way of indexing words. Helps find words which sound similar. • Forgiving Systems – Helps accommodate users mistakes by providing suggestions. • Free text retrieval systems – An index of every word in every document.

  8. Moore’s law • 1965 Gordon Moore, co-founder of Intel. • Number of transistors in a processor doubles every 18 years. • Computer memory - Doubling magnetic storage approximately every year.

  9. Effects of finite processor speed • Processing speed can cause faults if it’s too slow or too fast. • Functional fault - program does the wrong thing. • Buffers- Remembers key presses, mouse buttons and movements. Typically used if feedback is too slow, leading to strange effects at the interface.

  10. Limitations on interactive performance • Computation bound • 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 • Speed of memory access can interfere with interactive performance. • Graphics bound • Special-purpose graphics card to handle common graphics operations. • Network Capacity • Speed of the network rather than that of the memory which limits performance.

  11. Networked computing • Networked computers • Linked together in networks to increased computing power and memory. • Disadvantage – slow response time due to multiple users accessing single central machine, server down, lack of feedback.

  12. Internet • 1969 DARPANET when the US Government’s Department of Defense commissioned research into networking. 4 mainframes. • ARPANET – In 1971 renamed from DARPANET TO ARPANET. 23 mainframes. • Set of common languages(Protocols) • Transmission Control Protocol (TCP) moves data from A to B. • Internet Protocol (IP) specifies which B is being referred to so that data goes to correct place. • TCP/IP

  13. 2.10 Chapter 2 Summary • Input Devices – Main functions: text and pointing. • Text Input devices: QWERTY Keyboard, chord keyboards, telephone keypad, speech input. • Pointing devices: mouse, touchpad, trackball and joystick. • Screen Output devices • CRT and LCD screens. • Virtual reality and 3D spaces • Dataglove, body tracking, head mounted displays and cave environments.

  14. 2.10 Chapter 2 Summary • Printers – ink-jet, bubble-jet and laser printers, dot-matrix and thermal printers. • Scanners – convert printed images and documents into electronic form. • RAM – STM and LTM stored on optical and magnetic drives. • Access information - Multiple indices, free text databases, DWIM (do what I mean) and Soundex. • Processing speed is limited by various factors: computation, memory access, graphics and network delays.

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