1. 1 Lecture 2 I/O devices and networks Fundamentals of Computer Science Part i2

2. 2 Topics for this lecture Memory –primary, cache Storage devices –disks, CD-ROMs,… Input/Output –terminals, mice, printers,... Networks –LANs, WANs, MANs, WLANs

3. 3 Typical computing environment Several computers interconnected by a computer network, communicating with file servers, shared databases, printers, etc.

4. 4 Memory Primary memory –RAM (Random Access) –stores data and program Cache memory –fast, to improve speed

5. 5 Primary memory N cells Addresses 0..N-1 Each cell has k bits, hence 2 k distinct bit sequences that can be stored Ways of organising 96 bit memory...

6. 6 Cache memory 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.

7. 7 Storage devices High speed & cost, small size Low speed & cost, large size Magnetic disks: hard, floppy, scuzzy,... Optical disks: CD-ROM, CD-Writeable, DVD,...

8. 8 Magnetic disks Platter rotates under a head; magnetic coating reacts. Bits stored in tracks (concentric circles), split into sectors. Can be hard or flexible (floppy disk, diskette). SCSI (scuzzy) disks have high transfer rates.

9. 9 Optical disks CD-ROM (Compact Disk - Read Only Memory) CD-Rs (Compact Disk - Recordables) DVD (Digital Video/Versatile Disk); higher capacity. Higher capacity than magnetic disks. High power infrared laser burns holes in master. Copy made with bumps (pits) where the laser holes were.

10. 10 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).

11. 11 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

12. 12 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

13. 13 WANs Low bandwith, high latency Satellite/wire/cable Routers introduce delays MANs Wire/cable Range of technologies (ATM, Ethernet)

14. 14 The Internet & WWW The Internet –large, heterogeneous and open-ended WAN –connects home users and businesses World-wide Web: resource sharing over the Internet Based on technologies: –HTML (HyperText Markup Language) –URL (Uniform Resource Locator) –client-server architecture

15. 15 Internet Home intranet WAP gateway Host site Laptop Mobile Printer Camera Host intranet Wireless LAN phone The future is mobile...

16. 16 The future is home intranet... Wireless LANs (WLANs) –connectivity for portable devices (laptops, PDAs, mobile phones, video/dig. cameras, …) Home intranet –devices embedded in home appliances (hi-fi, washing machines, …) –universal ‘remote control’ + communication

17. 17 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 home intranets