The world without the internet

For many, it’s a scary thought. What if the internet simply disappeared tomorrow? What if all of the connections we held and activities we performed online were suddenly not available to us? These are questions that most would not want to answer even if they weren’t actively involved professionally online. Those of us who work online could be devastated.

In case you’re one of those who takes the world wide web for granted, here’s an infographic that takes us through the hypothetical scenario. The benefit, of course, is that more kids would go outside to play.

What is ADSL?

What is DSL..?
•A new technology came on the scene in recent years called DSL. 

•Digital Subscriber Line (DSL) is the generic name for a technology that allows digital data to


 sent over an ordinary copper telephone line at high speed.

•It is much faster than ISDN. For example in the UK it is common to have a 512Kbs service.


 Compare this to a dial-up service at 56Kbs or ISDN at 64Kbs

•There are more than one type DSL service. For example

–ADSL (Asymmetric Digital Subscriber Line)

–SDSL (Symmetric Digital Subscriber Line)

ADSL

>Providing bandwidth is expensive – it needs special  equipment at the exchanges and your

 telephone line has to be of good quality .

Cache Management: Watermarking

•Manage peak I/O requests “bursts” through flushing/de-staging

–Idle flushing, High Watermark flushing and Forced flushing

•For maximum performance:

–Provide headroom in write cache for I/O bursts

                        Idle flushing                 High watermark flushing              Forced flushing

XSS ( Cross Site Scripting)

Occurs any time…
• Raw data from attacker is sent to an innocent user

Raw data…
• Stored in database
• Reflected from web input (form field, hidden field, url, etc…)
• Sent directly into rich JavaScript client
• Virtually every web application has this problem
• Try this in your browser – javascript:alert(document.cookie)

Stored XSS

Components of Storage System Environment

Upon completion of this lesson, you will be able to:

•Describe the three components of storage system environment

–Host, Connectivity and Storage

•Detail Host physical and logical components

•Describe interface protocol

–PCI, IDE/ATA and SCSI

•Describe storage options

–Tape, optical and disk drives

Page Replacement Algorithms

There are many different page replacement algorithms. Probably every operating system has its own unique replacement scheme.

How do we select a particular replacement algorithm? In genrate, want the one with the lowest page fault rate.

We  evaluate an algorithm by running it on a particular string of memory references and computing the number of page faults. The string of memory references is called reference string.

We can generate reference string:

1.       Artificially(by a random number generator for example) or

2.       By tracing a given system and recording the address of each memory reference.

Structure of the Page Table in Memory Management

Each operating system has its own methods for storing page tables.

Most of them allocate a page table for each process. A pointer to the page table is stored with the other register values in the process control block (PCB)

Hardware Support

The hardware implementation of the page table can be done in a number of different ways.

Way – 1

Virtual Memory Technology

All previous discussed memory management schemes require that whole process to be in memory before process can execute. That’s why need memory management algorithms.

“Virtual Memory” is a technique that allows the execution of processes that may not be completely in memory.

Virtual memory is separation of user logical memory from physical memory. This separation allows that an extremely large virtual memory is to be provided for programmers when only a smaller physical memory is available.

Virtual memory is commonly implemented by “Demand Paging”.

BPEL Design Goals

There were ten original design goals associated with BPEL :

1.    Define business processes that interact with external entities through web service operations defined using WSDL 1.1, and that manifest themselves as Web services defined using WSDL 1.1. The interactions are “abstract” in the sense that the dependence is on portType definitions, not on port definitions.

2.    Define business processes using an XML-based language. Do not define a graphical representation of processes or provide any particular design methodology for processes.

Information Storage in facebook and youtube

Upon completion of this lesson, you will be able to:

• Describe the importance of information to individuals and to businesses

• Define data and information

• Discuss the categories of data

• Describe the storage architectures and their evolution

Why Information Storage

• “Digital universe – The Information Explosion”

– 21st Century is information era

Methods to Avoid Detection of Virus

• Same “last Modified” Date.
• Overwriting Unused areas of the .exe files.
• Killing tasks of Antivirus Software
• Avoiding Bait files & other undesirable hosts
•Making stealth virus
• Self Modification on each Infection
• Encryption with variable key.
• Polymorphic code


Same “last Modified” Date

• Same “last Modified” Date.
• In order to avoid detection by users, some viruses employ different kinds of deception.
• Some old viruses, especially on the MS-DOS platform, make sure that the "last modified" date of a host file stays the same when the file is infected by the virus.
• This approach sometimes fool anti-virus software.

Memory Management Algorithms

1. First-fit:

          It is simplest algorithm.

          Memory manager scans list of holes and allocate first hole that is big enough.

Searching always starts at beginning of set of holes and stop as soon as it finds a free hole this is large enough to satisfy memory requirement of current process.

Hole is broken into 2 parts. One for process and one create a hole except it is exact fit.

Advantage: it is fast because it searches as little as possible.

2. Next-fit:

It is a minor variation in first-fit.

Basic Memory Management in Operating Systems

Memory management systems can be divided into two classes:

1.    Those that move processes back and forth between main memory and disk during execution (swapping and paging) and

2.    Those that do not move processes back and forth between main memory and disk memory management scheme of Class 2 is discussed below.

1. Mono-programming Without Swapping or paging

To run just one program at a time, sharing memory between that program and OS is the simplest memory management scheme. Three variations on this scheme: Fig 1.1 

Virus & Worms – Virus Analysis

Spyware Overview 
• Spyware is a piece of software that gets installed on computer without your consent.
• It collects your personal information without you being aware of it.
• Change how your computer or web browser is configured and bombard you with online advertisements.
• Spyware programs are notorious for being difficult to remove on your own and slows down your PC.
• A program gets installed in the background while you are doing something else on Internet.
• Spware has fairly widespread because your cable modem or DSL connection is always connected.

REST (Representational State Transfer)

REST (Representational state transfer) is an approach for getting information content from a web site by reading a designated web page that contains an XML (Extensible Markup Language) file that describes and desired content.For example,REST could be used by an online publisher to make syndicated content available. Periodically,the publisher would prepare and activate a web page that include content and XML statements that described the content.Subscribers would need only to know the URL (Uniform Resource Locator) for the page.


where the XML file was located,read it with a web browser,interpret the content data using the XML information,and reformat and use it appropriately (perhaps in some from of online publication).