STORAGE / INTERNET

Spring 2010

What is Booting?

Cold boot Turning on computer that has been powered off

Warm boot Restarting computer that is powered on Warm boot from Windows

desktopWarm boot from system unit

Process of starting or restarting a computer

Image: © Shelly Cashman Vermaat 2004

Types of Memory

RAM (temporary/volatile) Random Access Memory (Primary Storage) Storage for programs and data “Workspace” for the CPU

ROM (permanent/non-volatile) Read Only Memory – does not change Startup instructions for computer (“Boot”) Or – more specialized applications like

games for small computers

Secondary Storage (or Storage) The place where software and data are

kept while not in use. Common types:

Magnetic (hard drive) Optical (CD, DVD) Integrated Circuit (Flash memory USB

sticks, Solid state drives, MP3 player)

Storage - Hard Disks

Step 1.Circuit board controls movement of head actuator and a small motor.

Step 2.Small motor spins platters while computer is running.

Step 3.When software requests a disk access, read/write heads determine current or new location of data.

Step 4.Head actuator positions read/write head arms over correct location on platters to read or write data.

Image: © Shelly Cashman Vermaat 2004

Hard Disks

clearance

read/write head

platter

hair

dustsmoke

A smoke particle, dust particle, or human hair could render drive unusable

Clearance between head and platter is approximately two-millionths of an inch

Image: © Shelly Cashman Vermaat 2004

Hard Disk Capacity

Image: © Shelly Cashman Vermaat 2004

Hard Drive Capacity Explained• If 1 GB = 1,073,741,824 (2^30), then

• 46,102,659,072 bytes / 1,073,741,824 = 42.9 GB

Disks What are tracks and sectors?

Trackis narrow

recording bandthat forms fullcircle on disk

Sector stores up

to512 bytes

of data

Formatting prepares disk for use and marks bad sectors as unusable

Image: © Shelly Cashman Vermaat 2004

Disk Defragmenter

file before defragmentingfragmented disk

file after defragmenting

Reorganizes files and unused space on hard disk so programs run faster

Image: © Shelly Cashman Vermaat 2004

Hard Drives

RPM- Revolutions Per Minute Examples: 7200 RPM, 5400 RPM, 4200 RPM

10,000 RPM

Desktop hard drives usually faster RPM than laptop

Solid State Hard Drive

Data storage device that uses solid-state memory to store data

Emulates a hard disk drive No moving parts, therefore less fragile

and quieter Solid State Drive - Wikipedia Link Laptops More $$$

Other Storage Devices? CD / DVD

Optical drives Laser light burns pits onto

surface Change in height) land to

pit, pit to land) =1, land=0 Single track that spirals

into the center CD - 650 MB to 1 GB DVD - 4.7 GB to 17 GB

Flash Drives Flash Memory Data

Storage Device 64 MB to 64 GB Connect thru USB port

Image from www.haimei.com

Image from www.digitalswirl.com

Flash Memory

Erasable, programmable ROM EEPROM Used for storage devices:

Digital cameras Home video game consoles

Memory Stick, SmartMedia, CompactFlash

BIOS Chip Howstuffworks.com link

Processing… Fastest Faster Fast

Applications

Today’s applications are LARGE in size Not practical to place all of an

application in memory while processing Multitasking

So – what is the solution???

Virtual Memory

Virtual Memory – using a portion of free hard drive space as memory.

Large enough to hold programs and data for all currently running applications

Use main memory as cache for files Just as cache memory, itself, is temporary storage for

CPU. Pages – blocks of hard drive space used for programs

and data

Virtual Memory

Virtual memory contains entire program and data for an application as it runs

RAM contains sections of the program and data recently used

Cache contains the most recent materials used in processing by the CPU

Programs and data moved on an ‘as-needed’ basis

Application Execution Progression…

Hard Drive

Virtual Memory on hard drive

RAM

Cache

CPU/registers

Virtual Memory

Step 1. The operating system transfers the least recently used data and program instructions to disk because memory is needed for other functions.

Step 2. The operating system transfers data and program instructions from disk to memory when they are needed.

Portion of free hard drive space that is used as RAM

Image: © Shelly Cashman Vermaat 2004

How Much Memory??

Depends … Enough to run desired programs and

plan for the future Applications increase in size with each

new version that is released! I would recommend at least: 2 GB – 4 GB RAM to start - more if you can afford it!

Thrashing

Constant movement of materials between disk and main memory

Why?? Memory too small Solution: Increase RAM

Terms – Storage

Boot (Warm/Cold) Disk Defragmentation Flash Memory Hard Disk Page Permanent Storage

(secondary) Platter RAM (temporary)

Read/Write Head ROM RPM Sector Storage devices

Hard Drive, Solid State Drive, CD, DVD, Flash, etc.

Track Thrashing Virtual memory

HOW DOES THE INTERNET WORK?

Spring 2010

What is the Internet?

The Internet involves millions of computers, connected in complex ways to a maze of local and regional networks

Network of Networks

Capital “I” in Internet

Origins of the Internet

1969 Department of Defense established

experimental network connecting 4 research computers

Called ARPANET 1980s National Science Foundation

involved Only scientific, research and academic

institutions (no commercial traffic)

Other Developments…

1989 - E-mail connectivity thru CompuServe and MCI Mail (restrictions lifted)

1991 – move towards private sector Network Access Points (NAPs) Now called Internet Exchange Points (IXPs)

Internet Service Providers (ISPs) Companies that connect users to Internet

Verizon, AT&T, Comcast, AOL, NetZero, etc. Communication coordinated through

national and international organizations (standards)

Connect to Internet Ways to connect

Dial-up Broadband

DSL (Digital Subscriber Service) Cable Modem Fiber-Optic Internet (Verizon) Satellite (via a dish)

ISP – Internet Service Provider Find one at www.thelist.com Individual users enter ISP through a POP (point of

presence) Access Point to Internet Physical location that houses servers, routers, switches,

etc. Bank of modems

ISPs maintain multiple POPs for geographic area they serve

Who Owns the Internet? No one company or country can be

considered as owner of Internet Ownership shared among various

entities Coordination:

Internet Society (ISOC) Internet Engineering Task Force (IETF) Internet Architecture Board (IAB) World Wide Web Consortium (W3C)

In the US – ICANN – Internet names and port

numbers

ICANN

Difference Between Internet and Web?

World Wide Web is just one of the services deployed on the Internet Subnetwork Linked documents, use of HTML Early 1990s – First browser

(graphics with text) Mosaic → Netscape

Other services deployed on the Internet include: E-mail, FTP, IM, P2P, Telnet, etc.

What is Internet2?

Internet Address

Find a Web Page?

IP Address

Computers

Static IP address Specified manually and entered into network

tables Permanent address Mostly for file servers

Dynamic IP address Dynamic Host Configuration Protocol (DHCP) Ask network for an IP address when you turn it

on (from a pool of available addresses) IP address changes each time computer is used Mostly for Clients (users)

My IP address at home 71.181.178.???

Web Browsers

Internet Explorer, Mozilla FireFox, Netscape Navigator, Opera, Apple Safari

System of communicating Web documents Hypertext Transfer Protocol (HTTP)

Protocol used to transfer Web pages Formatting instructions called:

HTML (Hypertext Markup Language)

HTML Tags

<html> </html> Begin/End of document

<b> </b> Bold

<p> </p> Paragraph

<title> </title> Title – top of window

<table> </table> Use in tabular form

<ol> </ol> Ordered List

<br> Break (new line)

<img src=“mypicture.gif”> Image

JavaScript – for Interactivity

Allows for local processing (on your machine) instead of on server (server-side processing)

Browser handles some processing chores before transmitting to server

Client-Side Processing Buttons, Check boxes, drop-down lists Error-checking

Advantage Faster response to user interaction

Disadvantage Opens user to possible risks (exploit weakness

in browser)

JavaScript Example<html><head><script type="text/javascript">function show_confirm(){var r=confirm("Press a button");if (r==true) { document.write("You pressed OK!"); }else { document.write("You pressed Cancel!"); }}</script></head><body>

<input type="button" onclick="show_confirm()" value="Show a confirm box" />

</body></html>

Terms – Internet ABILENE (Internet2)

ARPANET (Dept of Defense)

Cable-modem

Client-side processing

Dial-up

DSL

Domain name

DHCP

Domain Name Server

Dynamic IP address

Fiber-Optic

HTML

HTTP

ICANN (2009)

ISP

IP Number / IP Address

Internet2

JavaScript

MAC address

MAGPI

Mosaic / Netscape

National Science Foundation

POP

Satellite

Server-side processing

Static IP address

Top-level domain

WEB BROWSER

World Wide Web Consortium