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Computer Science HL

(updating weekly) Covering all topics needed to prepare for the CompSci Diploma exams

Anthony Russo

on 16 April 2015

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Transcript of Computer Science HL

Welcome to G11 CompSci SL/HL
Let's get started
Almost everything you need will be in the class Moodle
Using Moodle
We will use the class wiki to organize our research and to build a study guide
Using the Class wiki
Updating the class blog each week is essential!
Class Blog

Architecture synthesis
Computer Architecture
- OS
2.1.6, 2.1.7, 2.1.8,6.1.1, 6.1.5, 6.1.7, 6.1.9
- Primary and secondary memory
2.1.2, 2.1.3, 2.1.5
- Backup
1.1.11, 1.1.12, 1.1.13
- CPUs
2.1.1, 2.1.4, 2.1.9,2.1.10,2.1.11, 2.1.12,2.1.13, 4.3.1, 4.3.2, 4.3.4
- Control /Microprocessors
7.1.1, 7.1.2,7.1.3, 7.1.4,7.1.5,7.1.6
Describe Primary Memory.
Explain the use of cache memory
Identify the need for persistent storage.
Examples of ROM and RAM
It is small-sized, light, but quite expensive at the same time. (The particular types of RAM used for primary storage are also volatile, i.e. they lose the information when not powered)
ROM - Read Only Memory
ROM is internal memory in the computer which is used to store critical information required by the computer like booting programs. They are prerecorded and are read only
The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. The advantage of cache memory is that the CPU does not have to use the motherboard’s system bus for data transfer.
Persistent storage is needed to store data in a non-volatile device during and after the running of a program.
Persistent Storage
System Backup
Identify a range of causes of data loss.
Causes include malicious activities and natural disasters.S/E Malicious activity may be a result of activities by employees within the organization or intruders.
Outline the consequences of data loss
in a specified situation.
S/E Loss of medical records,cancellation of a hotel reservation without the knowledge of the traveller.
Describe a range of methods that canbe used to prevent data loss.
Removable media
Failover Systems
Offsite/online storage
Outline the architecture of the central processing unit (CPU)
The functions of the arithmetic logic unit(ALU)
The control unit (CU) and the registers within the CPU.
Explain the machine instruction cycle.
Define the terms: bit, byte, binary,denary/decimal, hexadecimal.
Denary/decimal = 0 1 2 3 4 5 6 7 8 9
Outline the way in which data
is represented in the computer.
To include strings, integers, characters and colours.
for example: The relation between the hexadecimalrepresentation of colours and the number of colours available.
Simple logic gates
Define the Boolean operators: AND,OR, NOT, NAND, NOR and XOR.
Construct truth tables using the above operators.
See assignment under Architecture
Construct a logic diagram using AND,OR, NOT, NAND, NOR and XOR gates.
State the fundamental operations of a
Add Data
Compare Data
Retrieve Data
Store Data
It is called the
Distinguish between fundamental and compound operations of a computer.
Fundamental Operations:
Compound Operations:
Find the biggest
Find the smallest
Compare data
Explain the need for higher level languages.
The amount of abstraction
provided defines how
"high-level" a programming
language is

Control /Microprocessors
Centralized Control Systems
Discuss a range of control systems.
Automatic Doors
Domestic Robots
Outline the uses of microprocessors and sensor input in control systems.
Use examples from above
Operation that uses multiple processes to come to one output.
Evaluate different input devices for the collection of data in specified situations.
Barcode Reader
Biometric Reader
EMR/BP Reader
Explain the relationship between a sensor, the processor and an output transducer.
Describe the role of feedback
in a control system.
Discuss the social impacts and ethical considerations associated with the use of embedded systems.
For example, tagging prisoners, surveillance, CCTV, improved safety systems.
Identify the limitations of a range of resources in a specified computer system.
Example: single processor computers may not be able to render 3D graphics effectively
Describe the possible problems resulting from the limitations in the resources in a computer system
User time wasted if the primary memory is too small or processor speed inadequate
Discuss the advantages of producing a dedicated operating system for a device.
Example: using a dedicated operating system for a cell phone rather than using a pre-existing operating system.
Other examples:
A computer with 1 GB of RAM trying to run Photoshop along other programs.
Connecting a 100Mb/s Ethernet connection into a computer with only 10Mb/s Ethernet compatibility.
User cannot run modern programs or graphically intensive programs due to outdated CPU and GPU.
Computer will be driven to critical system failure due to over stressing of the hardware to compensate for the hardware intensive process, resulting in overheating and damage to the hardware.

The operating system can be device specific: such as having touch screen driven system for touch enabled devices while having a button driven system for devices with buttons.
The operating system will be modified to include the needs of the device, leaving out unnecessary utilities that would have been included if a pre-existing OS would have been used.
The variety of operating system would conclude in making users having to re-learn the specific OS every time instead of having an unified OS.

Computer Networks
OSI Model
General Model
IP, TCP, FTP and standards
3.1.2, 3.1.6, 3.1.7, 3.1.11, C1.7
Layer 2 presentation - compression
3.1.9, C3.6, C3.7
Layer 7 - physical layer
Network speed (at different OSI layers)
Network security (at different OSI layers)
3.1.15, 3.1.16
Organization of Networks
3.1.4, 3.1.5
3.1.12, 3.1.13, 3.1.14
Ubiquitous computing, peer to peer, mobile computing, grid computing
C3.1, C3.2
Distributed networks
Cloud computing, client server
Networking Current Issues
- Cloud computing versus client server
Social issues relating to decentralization because of the web
Describe the role of network architecture, protocols and standards in the future development of the web
Are you having trouble remembering all 7 layers?
Look Here!
Open Systems Interconnection Reference Model = OSI
The OSI model is a layered model that describes how information moves from an application program running on one networked computer to an application program running on another networked computer. In essence, the OSI model prescribes the steps to be used to transfer data over a transmission medium from one networked device to another. The OSI model is a seven-layer model developed around five specific design principles:
If more detailed information about the OSI model is needed please visit the class wiki: http://dis-dpcs.wikispaces.com/OSI+Model
Describe how communication over networks is broken down into different layers.
Outline the importance of standards
in the construction of networks.
Standards enable compatibility through a common “language” internationally
Define the terms: protocol, data packet
Data Packet
Data Transmission
A standard set of regulations and requirements that allow two electronic items to connect to and exchange information with one another.
A packet is a basic unit of communication over a digital network
When data has to be transmitted, it is broken down into similar structures of data, which are reassembled to the original data chunk once they reach their destination.
Explain why protocols are necessary
Data integrity
Error Checking
without protocols we cannot send and receive information over a network.
Refers to the accuracy and consistency of data stored in a database or other construct.
Feedback-based flow control; the receiver sends back information to the sender giving it permission to send more data or tells the sender how the receiver is doing.
Rate-based flow control, the protocol has a built-in mechanism that limits the rate at which senders may transmit data, without using feedback from the receiver.
A deadlock is a situation in which two or more competing actions are each waiting for the other to finish, and thus neither ever does.
Explain how data is transmitted by packet switching
Internet data, whether in the form of a Web page, a downloaded file or an e-mail message, travels over a system known as a packet-switching network.

Each of these packages gets a wrapper that includes information on the sender's address, the receiver's address, the package's place in the entire message, and how the receiving computer can be sure that the package arrived intact.
Internet protocol (IP)

Transmission control protocol (TCP)
File transfer protocol (FTP).
Identify the characteristics of:
Network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates. This can lead to queuing delay, packet loss or the blocking of new connections.
Error checking is technique that enable reliable delivery of digital data over unreliable communication channels, such as channels that have channel noise. Errors may be introduced during transmission from the source to a receiver. Error checking allows detection and reconstruction of the original data.
Photo Credit: [http://deceptiveroom.blogspot.de]
The Internet Protocol (IP) is the principal communications protocol used for relaying datagrams (also known as network packets) across an internetwork using the Internet Protocol Suite responsible for routing packets across network boundaries. It is the primary protocol that establishes the Internet
TCP (Transmission Control Protocol) is a set of rules (protocol) used along with the Internet Protocol (IP) to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the individual units of data (called packets) that a message is divided into for efficient routing through the Internet.
File Transfer Protocol (FTP) is a standard Internet protocol for transmitting files between computers on the Internet. FTP is commonly used to transfer Web page files from their creator to the computer that acts as their server for everyone on the Internet. It's also commonly used to download programs and other files to your computer from other servers.
Layer 2 Presentation - compression
Explain why compression of data is often necessary when transmitting across a network.
Compression enables information to be sent rapidly.
Add a few more if possible:
Distinguish between lossless and lossy compression.
Avoids going over the bandwidth limit.
Lossy compression happens to image, voice and video files which do not need every bit of the file to recreate itself, therefore, degenerating in quality over time. GIf files are an exception.
However, data such as a text file, which needs all the bits of the file to recreate itself undergoes lossless compression.
Evaluate the use of decompression software in the transfer of information
Students can test different compression methods to evaluate their effectiveness.
Layer 7 - physical layer
Outline the characteristics of different transmission media
Characteristics include:
Explain why the speed of data transmission across a network can vary.
Nodal Processing
Transmission Delay
Propagation Delay
Packet header examination
Error checking

Packets are sent to a queue. The delay depends on the number of items in the queue.
L/R=Time to send bits into link
R= link bandwidth (bps)
L= packet length (bits)
Propagation Delay = d/s

d = length of physical link
s = propagation speed in
medium (~2x108 m/sec)

In a WAN the delay is in the order of milliseconds.
Network security (at different OSI layers)
Describe the different methods of network security.
Evaluate the advantages and disadvantages of each method of network security.
Wireless Encryption
Wired Equivalent Privacy (WEP)
Wi-Fi Protected Access (WPA)
Pre-shared Key (PSK)
User ID
Also known as a username, a user ID is the name a user logs in to a system with. Usually used alongside a password it is one half of a set of credentials a user knows in order to access a system
MAC Address
Physical Security
Something that is physically in the way of someone breaking into a system. E.g. a door, or walls, or security guards.
Its primary objective is to control the incoming and outgoing network traffic by analyzing the data packets and determining whether it should be allowed through or not, based on a predetermined rule set. It may be hardware or software.
One-factor authentication – this is “something a user knows.” The most recognized type of one-factor authentication method is the password.
Two-factor authentication – in addition to the first factor, the second factor is “something a user has.” Examples of something a user has are a device that generates a pre-determined code, a signed digital certificate or even a biometric such as a fingerprint.
Three-factor authentication – in addition to the previous two factors, the third factor is “something a user is.” Examples of a third factor are all biometric such as the user’s voice, hand configuration, a fingerprint, a retina scan or similar.
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. Can be described as Ethernet hardware address (EHA), hardware address or physical address. It is assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card's read-only memory, or some other firmware mechanism.
3.1.1 Identify different types of networks.
LAN - Local Area Network
WLAN - Wireless Local Area Network
SAN - Storage Area Network
VLAN - Virtual Local Area Network
PAN - Personal Area Network
P2P - Peer to Peer
Identify the technologies required to provide a VPN.
Evaluate the use of a VPN.
A secure network that uses primarily public, telecommunication infrastructures, such as the Internet, to provide remote offices or traveling users an access to a central organizational network.
Advantages and Disadvantages
Outline the advantages and disadvantages of wireless networks.
Describe the hardware and software components of a wireless network.
Describe the characteristics of wireless networks.
wireless networks have led to changes in working patterns, social activities and raised health issues.
Include: WiFi; Worldwide Interoperability for Microwave Access (WiMAX); 3G mobile; future networks
Ubiquitous computing, peer to peer,
mobile computing, grid computing
Define the terms: mobile computing, ubiquitous computing, peer-2-peer network, grid computing.
mobile computing
Compare the major features of:
grid computing.
peer-2-peer network
ubiquitous computing
WPA encrypts information, and checks to make sure that the network security key has not been modified.
WPA also authenticates users to help ensure that only authorized people can access the network.
There are two types of WPA authentication: WPA and WPA2.
WPA is designed to work with all wireless network adapters, but it might not work with older routers or access points.
WPA2 is more secure than WPA, but it will not work with some older network adapters.
WPA is designed to be used with an 802.1X authentication server, which distributes different keys to each user. This is referred to as WPA-Enterprise or WPA2-Enterprise.
It can also be used in a pre-shared key (PSK) mode, where every user is given the same password. This is referred to as WPA-Personal or WPA2-Personal.
WEP is an older network security method that is still available to support older devices, but it is no longer recommended.
When you enable WEP, you set up a network security key. This key encrypts the information that one computer sends to another computer across your network. However, WEP security is relatively easy to crack.
Every user is given the same password. This is used in WPA-Personal or WPA2-Personal.
MAC address
The advantage to MAC filtering is that there is no attachment cost to devices that connect to the network. The policy is set on a router or switch, and the equipment attached either is permitted or it is not. The person attaching the equipment has nothing to do.
The disadvantage to MAC filtering is that it is easy to spoof due to the broadcast nature of LAN and WLAN, one can sit on the wire and just listen to traffic to and from permitted MAC addresses. Then, that person can change his MAC address to a permitted one, and in most cases obtain access to the network.
The advantage of a firewall is that the user can monitor incoming and outgoing security alerts and the firewall company will record and track down an intrusion attempt depending on the severity. Some firewalls can detect viruses, worms, Trojan horses, or data collectors.The disadvantage of firewalls is that they offer weak defense from viruses so antiviral software and an IDS (intrusion detection system) which protects against Trojans and port scans should also complement your firewall in the layering defense. A firewall protection is limited once you have an allowable connection open. This is where another program should be in place to catch Trojan horse viruses trying to enter your computer as unassuming normal traffic.
The advantage of using a 3 factor authentication is that it's made reassuringly sure that the person who is authenticating is the person who is authenticating through multiple layers of security.
The disadvantage is that there is a possibility that the person trying to authenticate loses first or the second authentication, the process can also take time.
Peer-to-Peer: 9 Properties:
1. relevant resources located at nodes (“peers”) at the edges of a network
2. peers share their resources
3. resource locations widely distributed most often largely replicated
4. variable connectivity is the norm
5. combined Client and Server functionality
6. direct interaction (provision of services, e.g. file transfer) between peers (= “peer to peer”)
7. peers have significant autonomy and mostly similar rights
8. no central control or centralized usage/provisioning of a service
9. self-organizing system
C3.4 Describe the range of hardware used by distributed networks
Distributed networks
A processor (at least 1 GHz)
Memory and disk storage (at least 1.2 GB)
The best network connection possible
A video card supporting at least 64,000 colors and 1024 x 768 resolution
Cloud computing, Client Server
Describe how cloud computing is different from a client-server architecture.
client-server means there is some logical segregation of components, services, and resources. Typically we see user-interfaces in a local execution [aka "client"] and business and data store and other resources in a remote execution [aka "server"]

Some examples:

MSN Messenger [contains an application we run on our local machine, while a back-end service facilitates communication at a remote location]

Facebook [contains a thin application - our web browser - and a remote service - their servers]

StackOverflow [same Facebook]
Cloud computing is an abstraction of traditional server hosting solutions. Instead of buying 10 servers myself to run and manage in my own operations data center, I now lease X servers from a vendor where X is a variable number decided by me whenever I want
Networking Current Issues
C4.6 Describe the role of network architecture, protocols and standards in the future development of the web.
Welcome to System Design!
1.1.1 Identify the context for which a new system is planned.
The extent and limitations of a new system should be appreciated:
Printing System at DIS
Pros and Cons:
1.1.2 Describe the need for change management.
Helps ease in new systems, make sure existing systems work with the new one
What else do we need to know?
1.1.3 Outline compatibility issues resulting from situations including legacy systems and business mergers
Business mergers
legacy systems
Research this:
1.1.4 Compare the implementation of systems using a client’s hardware with hosting systems remotely.
Implementation of new systems (setting a new system in place)
Implementation of systems on client's hardware VS hosting systems remotely
1.1.7 Suggest various types of testing.
1.1.6 Discuss problems that may arise as a part of data migration.
1.1.5 Evaluate alternative installation processes.
Students should be aware of the methods of implementation/conversion.

Parallel running, pilot running, direct changeover and phased conversion.

S/E Training issues may require organizations to restructure their workforce.
(D3lta) Research Data Migration
What is testing?
Why do I need to test my system?
When should I test my system?
Show us different kinds of testing:
User Focus
1.1.8 Describe the importance of user documentation.
1.1.9 Evaluate different methods of providing user documentation.
1.1.10 Evaluate different methods of delivering user training.
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