Computing Flashcards by Boris Ledovskih

OSI Network Protocol Layers

Application
Presentation
Session
Transport
Network
Data link
Physical

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Computer system - Definiton

A computer system accepts data (in many forms)
Processes the data
Produces an output (information in many forms)

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Hardware

Is the physical computer with its peripherals such as monitor, keyboards and printers

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Software

Are the programs running on the hardware

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Data

Consists of the real world items represented on the computer such as text, pictures, sounds and documents

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Information

Consists of processed data

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The CPU

(Central Processing Unit)

The main task of the processed is to process (computer) raw data and produce the desired result

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Primary Storage (RAM)

Temporarily stores data and program instructions during processing

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Secondary storage (Hard Disk)

Devices that store data and programs when they are not being used in processing

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Input devices

Keyboard, scanner, mouse, microphone, digital camera/web cam

Takes data and converts them into electronic form for input into the computer

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Output Devices

Screen, printer, speaker, webcam

Converts electronic data produced by the computer system and display them in a dorm that people can understand

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Communication Devices

Network, WiFi…

Provide connection between the computer and communications networks

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System Buses

Buses (wires) are the channels through which electronic impulses travel from one component to another. In a three bus system, buses are specialised for Data, Adress, and Control signals.

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Memory Hierarchy Levels

Fastest

Registers
Caches
Memory
Disk
Tape

Largest

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What does memory store

Stores data and assembly instructions

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Registers

Temporary storage containers used inside the CPU
Extremely fast
Fixed size, usually multiples of 8-bits

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Virtual memory

If program is too big for memory (RAM) then the hard drive is used (disk) to store data temporarily

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Cache

Slower than registers
Faster than RAM
Located in front of main RAM
Different levels of cache
(Level 1 (L1) Level 2 (L2))
Size: 4 to 8 MB

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Memory Access Method: Direct Access

Also known as Random Access
No need to go through other data to get the data you want
We already know where the data is
Example: REGISTERS, CACHE, RAM

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Memory Access Method: Sequential Access

Also known as Serial-Access
Data is stored in some sequential fashion
To get your data, you need to go through other data in front of it

Example:
fast forwarding a cassette tape

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What is located in CPU?

Registers
Control Unit
Arithmetic & Logic Unit

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What is located in Memory?

RAM
RAM
More RAM…

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What is a Bit

1 bit is one binary digit of information

A bit can take only the value of 0 or the value of 1

Bits usually come in eights

An 8 digit binary number is called a byte

1KByte

1000 Bytes (10^3 Bytes)

1MByte

1,000,000 Bytes (10^6 Bytes)

1GBytes

1,000,000,000 Bytes (10^9 Bytes)

1TByte

1,000,000,000,000 Bytes (10^12 Bytes)

1KiBytes

1024 or 2^10 bytes

1MiByte

2^20 bytes

1GiByte

2^30 Bytes

1 TiByte

2^40 Bytes

CPU Instruction Set - CISC

Complex Instruction Set Coding Used in earlier x86 family processors Huger number of rarely used isn't ructions tended to be too complicated Processors were down and used a lot of power making them hot

CPU Instruction Set - RISC

Reduced Instruction Set Coding A much smaller set of generic instructions are implemented which are used in combination to produce complex outcomes Results in smaller chips which can be faster and dissipate far less heat

Von Neumann Model weaknesses

The program and data code uses the same channel slowing things down.

Harvard Architecture

The memory registers used for storing the program instructions is separate from those used for data Two sets of addresses and data buses are used between the CPU and memory This has some advantages and some disadvantages

Von Neumann Architecture

Simple way of designing a stored program computer Use the same electronic store for both instruction and data and route all transfers of any kind of variable through CPU Simplifies the construction, but slows things down limiting the speed which information can be moved

What is a protocol?

A set of rules

What is a Communications Protocol?

Definite formal order of messages that are exchanged between two communicating devices

``` All People Seem To Need Data Processing ```

``` Application Presentation Session Transport Network Data link Physical ```

OSI MODEL: Layer 1 (Physical)

Responsible to transmitting raw bits of data down a physical connection

OSI MODEL: Layer 2 (Data Link)

Responsible for transmission of data frames over a single physical link

OSI MODEL: Layer 3 (Network)

Responsible for transmitting packets over the emigre network or inter-network

OSI MODEL: Layer 4 (Transport)

Responsible for providing a reliable data transmission service over the network End to end communication

OSI MODEL: Layer 6 (Presentation)

(Optional layer) | Provides s further abstraction the session layer that provides useful transformations for the data

OSI MODEL: Layer 5 (Session)

This layer j flyers any optional protocols and services on top of a simple Transport Layer

OSI MODEL: Layer 7 (Applicstion)

Provides services directly to users of the OSI environment

Why are protocols layered?

Network Software is complex Promotes re-usability Allows network independence

TCP/IP Model

Application Layer Transport Layer Internet Layer Network Interface Layer

IP over everything... And everything over IP

Maintain IP-layer transparency IP will run on any link layer and any service will run on IP layer

Transport Control Protocol (TCP)

Deals with providing reliable transport on a network

Internet Protocol (IP)

Deals with addressing data to its final destination

IP Addressing

Each devise on an IP network must have an IP address: Two parts: - Network ID: identify the sub-network to which a host is attached - Host ID: identify a unique host on that sub-network

Lossless Data Compression

Can be restored perfectly to its original form

Lossy Compression

Non significant data can be discarded reducing file size

File types for Lossy Compression

JPEG | Music