Collegeboard Notes from Videos

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4.1 Notes: The Internet

Video 1: (4.1)

• CSN-1.A.1 A computing device is a physical artifact that can run a program. Some examples include computers, tablets, servers, routers, and smart sensors.

• CSN-1.A.2 A computing system is a group of computing devices and programs working together for a common purpose.

• CSN-1.A.3 A computer network is a group of interconnected computing devices capable of sending or receiving data.

• CSN-1.A.4 A computer network is a type of computing system.

• CSN-1.A.5 A path between two computing devices on a computer network (a sender and a receiver) is a sequence of directly connected computing devices that begins at the sender and ends at the receiver.

• CSN-1.A.6 Routing is the process of finding a path from sender to receiver.

• CSN-1.A.7 The bandwidth of a computer network is the maximum amount of data that can be sent in a fixed amount of time.

• CSN-1.A.8 Bandwidth is usually measured in bits per second.

Video 2: (4.1)

• CSN-1.B.1 The Internet is a computer network consisting of interconnected networks that use standardized, open (nonproprietary) communication protocols.

• CSN-1.B.2 Access to the Internet depends on the ability to connect a computing device to an Internet-connected device.

• CSN-1.B.3 A protocol is an agreed-upon set of rules that specify the behavior of a system.

• CSN-1.B.4 The protocols used in the Internet are open, which allows users to easily connect additional computing devices to the Internet.

• CSN-1.B.5 Routing on the Internet is usually dynamic; it is not specified in advance.

• CSN-1.B.6 The scalability of a system is the capacity for the system to change in size and scale to meet new demands.

• CSN-1.B.7 The Internet was designed to be scalable.

[Im2008]

Fault-Tolerant Systems and the Internet

Fault-Tolerance: process that enables an operating system to respond to a failure in hardware or software

Video 1: (4.2)

CSN-1.E

For fault-tolerant systems, like the Internet:

• a. Describe the benefits of fault tolerance.
• c. Identify vulnerabilities to failure in a system.

Key Concepts:

• CSN-1.E.1 The Internet has been engineered to be fault-tolerant, with abstractions for routing and transmitting data.
• CSN-1.E.2 Redundancy is the inclusion of extra components that can be used to mitigate failure of a system if other components fail.
• CSN-1.E.3 One way to accomplish network redundancy is by having more than one path between any two connected devices.
• CSN-1.E.4 If a particular device or connection on the Internet fails, subsequent data will be sent via a different route, if possible.
• CSN-1.E.5 When a system can support failures and still continue to function, it is called fault-tolerant. This is important because elements of complex systems fail at unexpected times, often in groups, and fault tolerance allows users to continue to use the network.
• CSN-1.E.6 Redundancy within a system often requires additional resources, but can provide the benefit of fault tolerance.
• CSN-1.E.7 The redundancy of routing options between two points increases the reliability of the Internet and helps it scale to more devices and more people.

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Video 2: (4.2)

CSN-1.E

For fault-tolerant systems, like the Internet:

• b. Explain how a given system is fault-tolerant.

Key Concepts:

• CSN-1.E.1 The Internet has been engineered to be fault-tolerant, with abstractions for routing and transmitting data.
• CSN-1.E.2 Redundancy is the inclusion of extra components that can be used to mitigate failure of a system if other components fail.
• CSN-1.E.3 One way to accomplish network redundancy is by having more than one path between any two connected devices.
• CSN-1.E.4 If a particular device or connection on the Internet fails, subsequent data will be sent via a different route, if possible.
• CSN-1.E.5 When a system can support failures and still continue to function, it is called fault-tolerant. This is important because elements of complex systems fail at unexpected times, often in groups, and fault tolerance allows users to continue to use the network.
• CSN-1.E.6 Redundancy within a system often requires additional resources, but can provide the benefit of fault tolerance.
• CSN-1.E.7 The redundancy of routing options between two points increases the reliability of the Internet and helps it scale to more devices and more people.

[Im2008]

4.3 Video Notes: Computing Models and Efficiency

Learning Objectives

CSN-2.A

• Compare problem solutions.
• Determine the efficiency of solutions.
• Describe the benefits and challenges of parallel and distributed computing.

CSN-2.B

• Describe benefits and challenges of parallel and distributed computing.

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Essential Knowledge

Sequential Computing (CSN-2.A.1)

• A computational model where operations are performed in order, one at a time.

Parallel Computing (CSN-2.A.2, CSN-2.B.1, CSN-2.B.2, CSN-2.B.5)

• The program is broken into multiple smaller sequential computing operations, some of which are performed simultaneously.
• Consists of both a parallel portion and a sequential portion.
• Scales more effectively than sequential computing.
• Efficiency is still limited by the sequential portion, meaning that at some point, adding parallel portions will no longer improve efficiency.

Distributed Computing (CSN-2.A.3, CSN-2.B.3, CSN-2.B.4)

• A computational model where multiple devices are used to run a program.
• Solves problems that a single computer cannot due to processing time or storage limitations.
• Allows larger problems to be solved more quickly than a single computer.

Efficiency Comparisons (CSN-2.A.4, CSN-2.A.5, CSN-2.A.6, CSN-2.A.7)

• Efficiency is measured by comparing how long different solutions take to complete the same task.
• A sequential solution takes as long as the sum of all its steps.
• A parallel solution takes as long as its sequential tasks plus the longest of its parallel tasks.
• Speedup is calculated as:

  Speedup = (Time taken sequentially) / (Time taken in parallel)