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Memories, I/O devices and Networks

Memories, I/O devices and Networks. L14 Guilin Wang School of Computer Science The University of Birmingham [adapted from Ata Kaban]. Topics for This Lecture. Internal (Primary/Main) Memories Main memory, cache External (Secondary) Memories disks, CD-ROMs,… Input/Output Devices

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Memories, I/O devices and Networks

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  1. Memories, I/O devices and Networks L14 Guilin Wang School of Computer Science The University of Birmingham [adapted from Ata Kaban]

  2. Topics for This Lecture • Internal (Primary/Main) Memories • Main memory, cache • External (Secondary) Memories • disks, CD-ROMs,… • Input/Output Devices • terminals, mice, printers, ... • Computer Networks • LANs, WANs, MANs, WLANs

  3. Typical Computing Environment A number of computers interconnected by a computernetwork, communicating with file servers, shared databases, printers, etc.

  4. Memory Hierarchy • Memory is used to store data and programs • Memory is organized into a hierarchy: • Internal memory - registers in CPU (closest to the processor) - cache (faster than main memory) - main memory (usually RAM, not ROM) http://www.maximumpc.com/files/u69/Memory.jpg External memory - magnetic disk (direct access) - optical disk, such as CD-ROM, CD-RW, DVD, … - magnetic tape

  5. Memory Hierarchy High speed & cost, small size Low speed & cost, large size • d

  6. Memory • The basic unit of memory is the binary digit, a bit. • Memories consist of a number of cells (or locations) • Each cell stores k bits (a word) • Each cell has its address, by which programs can refer to it. • Adjacent cells have consecutive addresses. • Some recent computers (e.g. IBM PC) use 8-bit cells. • A cell is the smallest addressable unit, though data can be transferred in much larger units (blocks of words). http://www.treehugger.com/files/2007/10/home_energy_usa.php

  7. Primary Memory Example: 3 Ways of organising 96 bit memory • N cells • Addresses 0…N-1

  8. Error-correcting Codes • To avoid possible errors in memories, error-detecting or error-correcting codes are used. (a) Encoding of 1100 (b) Even parity added (c) Error in AC

  9. Cache Memory Registers • fast memory • more expensive • usually small • Stores most heavily used memory words. • Logically, between CPU and main memory. • First look in the cache, then main memory.

  10. Magnetic Disks http://www.ptdd.com/datarecovery/hard-drive.htm

  11. Magnetic Disks • A disk consists of a few aluminum platters. • Each platter rotates under a head; magnetic coating reacts. • Bits stored in tracks (concentric circles), split into sectors. • Disks can be hard or flexible (floppy disk, diskette). • SCSI (scuzzy) disks have high transfer rates (5~320 MB/sec), though IDE disks are also popular.

  12. Magnetic Disks Cylinder: The set of tracks at a given radial position. A disk with four platters

  13. Optical disks • Higher capacity than magnetic disks. • High power infrared laser burns holes in master. • Copy made with bumps (pits) where the laser holes were. • CD-ROM (Compact Disk - Read Only Memory) • CD-Rs (Compact Disk - Recordables) • DVD (Digital Video/Versatile Disk); higher capacity.

  14. A computer with I/O devices • A single bus (often there are two or more). • A bus arbiter, to resolve conflicts over simultaneous access. • A controller for each device. • Various I/O devices (keyboard/mouse, monitor, printer, modem, camera, mike, CD, DVD, etc).

  15. Computer Networks • Computer network: many connected computers for exchanging information. • Essence: packet-switching • Topology architecture: http://en.wikipedia.org/wiki/File:NetworkTopologies.png

  16. Computer Networks • Network Protocols: rules to guarantee that packets transmission can be conducted properly. • Combining networks: connect via repeater, bridge, switch and router. • Routing information computer Internet Router WiFi AP WiFi AP Router Router Laptop

  17. Types of Computer Networks • LANs (Local Area Networks) • technology suitable for small area, usually wire/fibre • WANs (Wide Area Networks) • large distances, inter-city/country/continental • the Internet • MANs (Metropolitan Area Networks) • intra-city, cable based, multimedia • Wireless networks • WLANs, WPANs

  18. LANs • Local Area Networks • within an institution, home, etc • High bandwith (total amount of data per unit of time) • Low latency (time taken for the first bit to reach destination) • Technology • predominantly Ethernet, now 100~1000Mbps

  19. WANs • Low bandwith, high latency • Satellite/wire/cable • Routers introduce delays MANs • Wire/cable • Range of technologies (ATM, Ethernet)

  20. The Internet & WWW • The Internet • large, heterogeneous and open-ended WAN • connects home users and businesses • World-wide Web: resourcesharing over the Internet • Based on technologies: • HTML (HyperText Markup Language) • URL (Uniform Resource Locator) • client-server architecture

  21. The future is mobile... Internet WAP Host intranet Home intranet Wireless LAN gateway Mobile phone Printer Laptop Host site Camera

  22. The future is home intranet... • Wireless LANs (WLANs) • connectivity for portable devices (laptops, PDAs, mobile phones, video/dig. cameras, …) • Homeintranet • devices embedded in home appliances (hi-fi, washing machines, …) • universal ‘remote control’ + communication

  23. Summary • Conventional I/O devices • memory and external storage • increasing variety of I/O devices (multimedia - sound, video, etc) • Networks for sharing and communication • Current & future developments • increasing of personal & mobile devices • growth of homeintranets

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