Notesale: Turn your study into money

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General Notes
7/03/17
LI: (2
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9 -> ) Binary, Hexadecimal, encoding definitions
Bit: The smallest amount of data that can be represented
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Represented as either 0 or 1
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g Boolean)
Byte: 8 bits
Denary/Decimal: The base 10 counting system
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Hexadecimal: The base 16 counting system
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Since 24 = 16, one Hex digit can be used to represent 4 bits, and two Hex digits
can be used to represent a byte
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n bits can take on 2n different values
Bit depth - colour depth is the number of bits per pixel
Obvious trade-off between picture quality vs file size
Only need 1 bit to store black and white
Question:
• A: Each pixel can represent 256 colours
• A: 480 000 bits = 60 000 bytes
• A: Colour depth is the number of bits per pixel
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However, it will increase the file size
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[8 marks]
Fetch, Decode, Execute, Store
Draw a block diagram showing the basic components of the CPU and how they interact with memory [8 marks]
• You need to be able to reproduce a block diagram
• 3 things that are important - Control Unit, Registers, Arithmetic Logic Unit
MAR - Memory address register
The address where it's going to store data
MDR - Memory data register
Register definitions in powerpoint
Don't reproduce all information for instruction cycle - just understand them

14/03/17
Outline two functions of an Operating System [4 marks]
An operating system is software that controls the main functionality of a program
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File management - allocating memory to applications, storing & retrieving files
User interfaces - controls the layout of user interface
IB Question - Outline ALU
cache
(Primary) Memory (RAM) volatile
Secondary Memory (hard disk) non-volatile
Volatile memory is not going to last (won't be there next time you turn on)
Non-volatile will be there
IB Exam direct take: Explain how customer's data can be secure when two customers access a system at the same time [2 marks]
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15/03/17
Q: Explain the use of cache memory [2 marks]
Cache memory is fast and volatile
Faster to retrieve frequently used data from the RAM
The purpose of cache memory is to set aside addresses and data so that it may be retrieved more quickly
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Q: Describe primary memory [2 marks]
Primary memory is the main components of a system that holds data
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Volatile
Faster to access than secondary memory
Examples
System's volatile storage area
Functions when the computer is turn on
Access directly by the processor
Q: Identify the need for persistent storage
Persistent storage is needed in order to store important data that will be used by the processor
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Important data
Still there after computer is turned off

Topic 2 Page 2

2
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1 Computer organisation (6 hours)
Computer architecture
Secondary memory
Operating systems and application systems
Binary representation
Simple logic gates

Topic 2 Page 3

Computer architecture
Topic

Class Notes

Organised Notes

2
...
1 Outline the architecture of • Draw a block diagram showing the basic
the central processing unit (CPU) components of the CPU and how they
and the functions of the
interact with memory [8 marks]
You need to be able to reproduce a
arithmetic logic unit (ALU) and
the control unit (CU) and the
block diagram
registers within the CPU
...
It controls the inputs and
outputs and how they interact with other components
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Registers are the smallest and fastest units of memory in a computer system
...
e
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The memory address register (MAR) holds the address of the memory that will be read from or
written to
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The
MAR gives the address of data to the MDR
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2
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2 Describe primary memory
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The memory is
volatile which means that the data exists only when the computer is powered
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→ Registers
→ Cache
→ Random access memory (RAM) which is used to hold data and instructions from running programs
→ Read-only memory (ROM) which is the non-volatile memory that is used to hold the operating system's
bootstrap loader or BIOS

2
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3 Explain the use of cache
memory
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• Feature - small, fast memory, used to hold
The purpose of cache memory is to set aside addresses and data so that it may be retrieved more
very frequently used data
quickly
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• Cache is faster than RAM
•

2
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4 Explain the machine
instruction cycle
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[8 marks]
• Fetch, Decode, Execute, Store

Topic 2 Page 4

The machine instruction cycle is a process that repeats until a computer is turned off
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This involves the MAR
passing the address of the next instruction to address bus, the data at that address being read into
the MDR, and it returning to the CPU via the data bus
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It involves the instruction carried by the MDR being
copied to the IR where it is translated into a format that the ALU can understand
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This is the stage where the ALU carries out the
operation
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Store - is when the control bus carries a "write" signal and data stored in the MDR is written into the
location of the MAR address
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You just have to understand
them
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1
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•

Persistent storage is needed in order to store important data that will be used by the processor
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Examples of secondary memory include:
• Disk storage
• Magnetic tape storage
• USB flash drive storage
• Hard Disk Drives (HDDs) and Solid State Drives (SSDs)e

Topic 2 Page 5

Operating systems and application systems
Topic

Class Notes

Organised Notes

2
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6 Describe the main
functions of an operating
system
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• Main functions
• A collection of programs
• Input/Output (IO) control
• File management
• Software/hardware interface
• Memory management
• User interface
• Scheduling
• Program execution control
• Security
• How many operating systems can you name?
MacOS
Windows
Linux
iOS
Android
ChromeOS
Etc
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Two functions of an operating system:
• File management - allocating memory to applications, storing & retrieving files
• User interfaces - controls the layout of user interface
An operating system is stored on a non-volatile hard-disk
...
Examples
include:
→ Word processors which handle text document management
→ Spreadsheets that conduct mathematical and financial calculations
→ Databases which organise information
→ Emails which electronically send mail
→ Web browsers which allow users to view HTML pages via the internet
→ Graphics processing that can edit, crop and enhance images, and
→ Computer-Aided Design (CAD) which are used to create and edit engineering and manufacturer
designs

2
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7 Outline the use of a range
of application software
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2
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8 Identify common features
of applications
...
1
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Short for "binary digit"
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Represented as either 0 or 1
...
g Boolean)
• Byte: 8 bits
• Denary/Decimal: The base 10 counting
system
...

• Hexadecimal: The base 16 counting system
...
Since 24 = 16, one Hex digit can
be used to represent 4 bits, and two Hex digits
can be used to represent a byte
...
1
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• Byte - memory tends to be divided up into
chunks
• 8 bit: 256 possible values
• 8 bits in a byte
• 16 bit: 65536
• Need computer to understand what letters are
• ASCII 7/8 bits
• Unicode 8/16/32 bits
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It is short for 'binary digit'
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A byte is 8 bits
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The normal place-value counting system in
which a new column is created when a power of 10 is reached
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Requires six new symbols in addition to 0-9, which
are A-F
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PowerPoint:
The most basic point is that more bits allows more different values to be stored
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How many different colours can each pixel represent? [2 marks]
Each pixel can represent 256 different colours
What is the size of the file? [2 marks]
480 000 bits = 60 000 bytes
A friend argues that if you increase the colour depth of this file, you will improve its quality
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1
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Compares 2 Values
• Unary - 1 (NOT)
2
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12 Construct truth tables
using the above operators
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1
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Topic 2 Page 8

Organised Notes
NOT turns the value into the opposite value
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NOR is the opposite of OR
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