Unit 1

What is a basic computer system made up of?

hardware and software

what is hardware

any physical component that makes up a computer

what is software

any program that runs on a computer

Name 4 examples of computer systems all around us

• mobile phones

• cash machines

• supermarket tills

• engine management systems in cars

What must all computer systems have

• a central processing unit, CPU (also called simply processer)

• at least one input device

• output device

• memory (primary storage)

what do input devices do

take real world data and convert it into a form that can be stored on a computer

give 3 examples of output devices

• a conventional computer screen

• an actuator that opens or closes a greenhouse window

• the speaker that produces sound on a phone

those are the 4 basic components needed, but what is the fifth component?

secondary storage

What is von neumann architecture?

It uses the idea of holding both programs and data in memory, data would then move between the memory unit and the processer

what did john von neumann himself develop

the concept of the stored program computer in the 1940s

What is the cpu and its function?

Of a computer is the hardware that executes programs and manages the rest of the hardware

What is cache memory?

very fast memory close to the cpu used to temporarily hold data or instructions that are likely to be needed again by the processer in the course of running a program

For a program to be run (executed) on a computer, where does it first have to be loaded?

into main memory

from here it can be accessed by what?

by the processer which runs each instruction in turn

when the program is loaded, what is the processer given?

the start address of where it is held in main memory

What is the cycle the processer uses

fetch-decode-execute cycle

what does the processer contain?

the control unit (CU), the arithmetic logic unit (ALU), registers

what does the control unit do and summarise its functions

it coordinates all the activities taking place inside the CPU

• controls the execution of instructions in the correct sequence

• decodes instructions

• regulates and controls processer timing using regular pulses from the system clock

• sends and receives control signals to and from other devices within the computer

what does the alu do

• logical operations: These include AND, OR and NOT

• shift operations: The bits in a computer word can be shifted left or right by a certain number

  of places.

• arithmetic operations: The bits in a computer word can be shifted left or right by a certain number

  of places.

what is a register?

a special very fast memory location within the CPU used in the execution of instructions

Describe the different special purpose registers in the CPU

• The Memory Address Register (MAR) holds the address (location in memory) of the

instruction or piece of data to be fetched or stored.

• The Memory Data Register (MDR) holds data or a program instruction temporarily when it

is fetched from memory or is to be sent to memory.

• The Program Counter (PC) holds the memory address of the next instruction to be processed.

• The Accumulator (ACC) is a special-purpose, memory location in which results of operations

carried out in the ALU are temporarily stored. (N.B. Most processors have several general-

purpose registers, instead of a single accumulator, which are used as temporary fast storage.)

What are the main factors affecting CPU performance?

• clock speed

• cache size

• number of cores

What is clock speed and what is it measured in?

The speed at which the processer operates, hertz

what is hertz the name for?

the number of cycles per second, or the rate at which the electrical current changes in the actual circuits

What does everything the processer does occur at?

the ‘tick’ of the clock

What are typical speeds for a PC?

2GHz to 4GHz

What is main memory known as?

Random Access Memory

Why do modern computers need lots of memory?

They need to run many programs at the same time

What does there need to be a compromise between concerning memory?

speed and cost

What is one way of improving speed at minimal cost?

use a small amount of cache, much faster (but more costly) memory where frequently used instructions or data can be stored temporarily

describe cache memory

Cache memory is an intermediary between main memory and the CPU. The cache makes any

data frequently used by CPU available much more quickly. Because the processor has to access

main memory less often, it can work faster, so the CPU performance increases. If the required

information is not located in the cache, it has to be fetched from RAM.

How much RAM and cache might a typical PC have as an example?

8 or 16GB of RAM but only 2MB of cache (therefore thousands more RAM than cache)

The more cache memory a computer has, then what?

The more data and instructions can be held in cache and made available very quickly, this improves processer performance

Describe the different levels of cache

• level 1 cache is extremely fast but small (between 2-64KB), thus speeding up the fetch-execute cycle

• level 2 cache is fairly fast (still much faster than RAM) and medium-sized (256KB-2MB)

• some CPUs also have level 3 cache

What does a dual-core processer have?

And quad-core?

What does this mean can take place?

• 2 processing units within the CPU

• 4

• parallel processing - 2 or 4 instructions being executed simultaneously

A program is a series of instructions that need to be done in order. Multiple cores could work on different programs that operate in parallel but unless the computer is … … … … …, a quad-core processor isn't necessarily four times faster. However, a PC with a multi-core processor, executing many tasks at the same time, will operate faster than a single-core processor.

designed to use multiple cores

what is an embedded system?

name a few examples

a small computer built into a piece of equipment designed to perform a specific functions

• vehicles, cameras, medical equipment, aircraft, vending machine, ovens, fridges, mobile phones, satellite navigation devices, televisions, digital clocks and lifts

What are the main characteristics of an embedded system?

reliability and minimal resources such as ROM, timers, sensors and actuators

Where is the program that controls the equipment held in?

ROM, cannot be changed

What language is the program written in? why?

machine-efficient language so that it uses minimum amount of memory and executes as fast as possible

It has a very … operating system. Unlike the operating system in a desktop computer, the embedded operating system does not have to be loaded when the machine is switched on, as it is held in ROM. The operating system is only able to run a single application.

limited

What is the user interface like?

very simple, such as the buttons on a microwave oven or washing machines

some embedded systems have no user interface

Some embedded systems have sensors designed to what?

give an example

• measure external stimuli and react accordingly

• a central heating system may use buttons and sliders to make the heating some on at certain times of day, on different days, and maintain a chosen temperature

What two distinct groups can memory and storage devices be split up into?

• primary storage (memory)

• secondary storage

What are offline storage devices?

storage devices that can be stored away from a computer. secondary storage devices are typically an integral part of the computer

What is RAM?

what does random access refer to?

where may memory space become available as files are deleted?

• the type of memory used as the computer’s main memory

• the fact that data may be written anywhere in that memory space at any time

• anywhere in RAM as files are deleted. this space can be reused

when a program is to be executed, it has to be loaded into what and why?

from the hard disk into main memory so that the processer can access the instructions, any data needed for that program to run is also loaded into main memory

what is the main purpose of RAM?

to act as temporary storage for programs and data while the program is being executed

why doesn’t the processer get the instructions straight from the hard disk?

reading from and writing to a hard disk is very slow compared to the speed of the processer

what is virtual memory and what is it used for?

describe it

• where part of the hard disk drive or solid state drive behaves like main memory when there isn’t enough main memory to store the whole of a program

• stores parts of programs currently being run but the parts actually being executed still need to be in main memory

• as the processer gets to next part of the program, sections are swapped between virtual memory and main memory

• sometimes this works well but sometimes computer spends more time swapping data than it does executing the program

what is the volatility of HDD and SSD memory?

non-volatile

what is the volatility of RAM and what does this mean?

volatile, when you turn off your computer it loses its contents

When you turn the computer back on it needs to get the basic startup routine from somewhere that is not … . The operating system and all your programs will be stored on the HDD/SSD but these need to be loaded into … to run.

• volatile

• RAM

What is the bootstrap loader?

a small program that loads the operating system

What does it mean to boot up a computer?

to start it up from scratch

Describe ROM

• read only memory

• you can not write over the contents once it has been created

• non-volatile, you can leave the computer switched off for months and it will start up as soon as it has power again

• used to store BIOS / bootstrap loader which is required at the start up of the computer

What is secondary storage’s volatility?

How much data does it hold compared to main memory as well as its price compared?

How are their access speeds compared to main memory?

• non-volatile

• generally much more than main memory, and relatively inexpensive per MB

• slower access speeds than main memory

What does secondary storage need to be?

robust and reliable

what 6 things do you need to consider with secondary storage?

• capacity

• speed

• portability

• durability

• reliability

• cost

Describe magnetic disks

• read with moving head inside disk drive

• has moving parts

• vulnerable to magnetic fields

• can be either internal or portable

• huge capacity therefore suitable for desktop purposes

• Smaller, denser surface areas spinning under the read-write heads mean that newer disks have capacities of several terabytes.

what are some downsides to moving parts?

• slow to read from or write to

• also make disk more susceptible to damage

compare internal hard disks and portable hard disks in:

1. physical size

2. cost

3. capacity

4. data transfer speed

5. portability

6. durability

7. reliability

8. typical use

1. 3.5 inches, 2.5 inches

2. for both, 8TB for £120

3. up to 15TB, 1TB to 16TB

4. 100-200MB per second, 100-200MB per second

5. not portable/built into PC , can fit in a large pocket

6. For both, good durability when disk not in use but vulnerable to movement when spinning. can write to the disk an infinite number of times. affected by heat and magnetic fields

7. for both, extremely reliable

8. inside a PC as secondary storage, supplementary storage for a PC or portable storage where high capacity is required

What are solid state drives?

Secondary storage devices with no moving parts and don’t rely on magnetic properties, so are unaffected by magnetic fields

what are the main benefits of SSD technology compared to HDD

• they are more reliable, being less susceptible to shock and damage as they have no

moving parts

• they are considerably lighter (which makes them suitable for laptops, tablets and other

modern devices)

• they have faster access times than HDDs because they don't have to wait for the head to

move and for the drive to spin

• they have lower power consumption

• they run much cooler than HDDs (both these points also make them very suitable for

laptop computers)

• because they have no moving parts, they can be very thin.

Where is SSD technology also used in?

memory sticks (pen drives) and memory cards

what are key features in SSD devices?

small size, non-volatile memory, reliability

Describe internal solid state drives, in terms of the 6 things you need to consider with secondary storage plus typical uses

1. Cost: 4TB for £400

2. Capacity: Up to 4TB

3. Data Transfer Speed: Up to 3.5GB/s (faster than magnetic disk because no moving parts)

4. Portability: Not portable, built into PC

5. Durability: More robust than hard disks with moving parts; said to be 5–10 times more durable than a hard disk drive

6. Reliability: Extremely reliable

7. Typical Use: PCs, notebooks, tablets, laptops

Describe USB Memory Sticks, in terms of the 6 things you need to consider with secondary storage plus typical uses

1. Cost: 256GB for £20

2. Capacity: 16MB to 256GB

3. Data Transfer Speed: 3–100MB/s

4. Portability: Very small; can be put in a pocket or on a key-ring

5. Durability: Very durable — some can be snapped quite easily

6. Reliability: Very reliable, but can corrupt files if removed from PC too soon

7. Typical Use: Personal use, moving files between computers

Describe Memory Cards, in terms of the 6 things you need to consider with secondary storage plus typical uses

1. Cost: 128GB SD card £15

2. Capacity: 32GB to 1TB

3. Data Transfer Speed: Dependent on type of card and device interface

4. Portability: Very small, designed for portable devices

5. Durability: Very durable — not sensitive to temperature or knocks

6. Reliability: Very reliable

7. Typical Use: In phones and cameras

What do optical media include?

CD, DVD and Blu-ray discs

How does optical media work?

Lasers write data to the disc and read data from it

What 3 formats do CDs come in?

• read-only (CD-ROM)

• recordable (CD-R)

• rewritable (CD-RW)

A CD-ROM is ‘…’ with the data at the time of manufacturing

pressed

Do optical storage devices have moving parts?

What does this mean for them compared to SSDs?

• yes

• access speeds and data transfer speeds are relatively slow in comparison with SSDs