3.4 Computer Systems

Question 1

L1
1) What is a computer?
2) How can computer systems be categorised?
3) What do these systems mean?

Answer 1

1) A computer is a programmable device that takes in data, processes it into useful information, and then outputs the information so it can be used.
2) Computer systems can be categorized as either:
- General purpose
- Embedded systems
3) General purpose computers are devices that have a variety of uses, the user chooses the task for the computer to complete.
An embedded system is a computer system with a specific purpose or function, which is built into a physical device or machine.

Question 2

L1
1) Describe a general purpose system
2) Describe an embedded system

Answer 2

1) General purpose:
- Used for many different types of tasks
- Lots of resources — memory, storage, CPU cores
- Most tasks require a user
2) Embedded systems:
- Specialised to a specific task/set of tasks
- Limited resources
- Often function without a user

Question 3

L1
Explain the different Start Up Sequence Components
1) The CPU
2) The RAM
3) The ROM
4) The hard drive
5) The BIOS

Answer 3

1) CPU: The central processing unit, is a large chip inside the computer that controls everything.
2) RAM: Random access memory, is read and write. It stores instructions and data ready for a CPU to execute.
3) ROM: Read-only memory, it stores permanent instructions that tells a computer how to ‘boot up’.
4) The hard drive: the main storage device in your computer. It stores files, folders, and the operating system.
5) BIOS: Contains all the basic code for controlling your computer hardware (such as keyboards, mice, monitors, and hard drives).

Question 4

L1
Explain how the Start Up Sequence works in order

Answer 4

1) The boot sequence begins
2) The CPU starts up and fetches the BIOS from ROM
3) Instructions from BIOS are loaded into RAM
4) BIOS starts up the monitor and keyboard
5) BIOS checks your computer is working
6) Operating system is fetched from secondary storage
7) Operating system is loaded into RAM
8) The BIOS hands over control to the operating system

Question 5

L1
1) What is system/ utility software, and list 3 examples?
2) What is computer architecture?
3) What type of architecture do modern computers use?

Answer 5

1) System software controls and runs the computer, allowing it to function, and manages the hardware and application software. It includes encryption software, data compression software, and backup software.
2) Computer architecture is a term used to describe the design of a computer system.
3) Modern computers use the von Neumann architecture designed by John von Neumann.

Question 6

L1
1) What is application software?
2) List 6 examples of application software.
3) What is the difference between system (utility) software and application software?

Answer 6

1) Application software is used to execute end-user tasks.
2) Examples include:
- Word processor
- Spreadsheet
- Presentation
- Database
- Web browser
- Media player (video/ music player)
3) System software manages the computer hardware and application software, whereas application software is for end-user tasks.

Question 7

L2
1) What are the key components inside the CPU?
What are the functions of these CPU components:
2) Control unit
3) Arithmetic logic unit

Answer 7

1) CPU stands for central processing unit.
Inside of the CPU, there are a number of key components:
1. Control unit
2. Arithmetic logic unit
3. Buses
4. Registers
5. Clock
2) Control unit: it decodes the instruction, and controls the fetching, writing and transfer of data between different components.
3) Arithmetic logic unit: it executes mathematical and logical instructions.

Question 8

L2
What are the functions of these CPU components?
1) Buses
2) Registers
3) Clock

Answer 8

1) Buses: many parallel wires connecting components, which transfer data or instructions between different CPU components.
2) Registers: holds data used when executing an instruction, and holds the result of executing an instruction.
3) Clock: it controls the number of instructions carried out each second and manages cycles per second.

Question 9

L3
1) What is the fetch-decode-execute cycle?
2) How does the fetch stage work?
3) How does the decode stage work?
4) How does the execute stage work?

Answer 9

1) The fetch-decode-execute cycle describes the basic operation of modern computers.
2) Fetch: the next instruction is fetched to the CPU from main memory.
3) Decode: the instruction is decoded to work out what it is.
4) Execute: the instruction is executed (carried out). Data may be fetch from main memory, or the result of the cycle may be stored in main memory.

Question 10

L3
Explain the fetch-decode-excecute cycle in detail

Answer 10

Instructions are loaded into RAM from secondary memory.
The instructions are stored in RAM in numbered memory locations.
Fetch:
The CPU sends a signal along the address bus requesting an instruction from a specific numbered location in RAM.
The instruction is transferred via the data bus to the CPU.
Decode:
The CPU decodes the instruction.
The CPU may fetch data held in memory if referenced in the instruction.
Execute:
The CPU executes the instruction.
The result may be stored back into RAM.

The cycle repeats.

Question 11

L4
1) What does RAM and ROM stand for?
2) What are RAM and ROM both types of?
3) What is memory used for?

Answer 11

1) RAM: Random access memory
ROM: Read-only memory
2) RAM and ROM are both types of main memory.
This means that they are directly accessible by the CPU.
3) Memory is used to store instructions for the CPU to execute.
They are much faster to access than secondary storage — i.e. a hard drive.

Question 12

1) What is the function of ROM?
2) What is the function of RAM?
3) What will happen if the computer does not have enough RAM?
4) How are the instructions used as the program executes, in terms of which components store the instructions in each step?

Answer 12

1) ROM is read only. It stores permanent instructions that tell a computer how to ‘boot up’.
2) RAM is read and write. It stores instructions and data ready for a CPU to execute.
3) If a computer system does not have enough RAM, it will run slowly.
4) As a program executes, the instructions are loaded into RAM from secondary storage. The CPU then takes the instructions from RAM and executes them.

Question 13

L4
1) What does volatile mean?
2) What does non-volatile mean?
3) Is RAM volatile or non-volatile, and approximately how much storage is it?
4) Is ROM volatile or non-volatile, and approximately how much storage is it?

Answer 13

1) Volatile is a term that means ‘data is lost when the power is switched off’.
2) Non-volatile means it ‘does not lose data when the power is switched off’
3) RAM is volatile, and is approximately 1–256GB.
4) ROM is non-volatile, and is approximately 6–8MB.

Question 14

L5
1) State 2 reasons why secondary storage is necessary
2) State the 3 categories of secondary storage

Answer 14

1) Secondary storage is necessary because:
- It stores all the users files, applications and software.
- It stores data when the computer is switched off, on a long-term basis.
2) The three categories of secondary storage are: solid state, optical and magnetic.

Question 15

L5
1) What are solid-state storage devices?
2) What is optical storage?
3) What is magnetic storage?

Answer 15

1) Solid-state storage devices, also called flash memory, have no moving parts. They store data inside electronic circuits, which can be set to store a 1 or 0. They can have a large capacity, but are more expensive.
2) Optical storage is most commonly used to distribute media and software. It uses lasers to read and write data on a reflective surface. These devices are typically small in capacity, but very cheap to produce.
3) Magnetic storage is the oldest form of storage. Data is stored in series as polarised dots. The polarity (positive or negative) of the dot determines whether it stores a 1 or 0. These devices come in very large capacities and are generally inexpensive.

Question 16

L5
1) What are the characteristics of solid-state storage?
2) What are the advantages of solid-state storage?
3) What are the disadvantages of solid-state storage?

Answer 16

1) Solid-state consists of:
- No moving parts to read or write data
- A collection of circuits wired together to store binary data
- The collection of circuits are wired to form a grid
2) Advantages of solid-state storage:
- Fast
- Lightweight
- Durable: they last a long time as they have no moving parts
- Low power consumption
- Silent when in use
3) Disadvantages of solid-storage:
- Expensive cost per MB
- Typically a lower capacity than hard drives
- They have limited read/writes

Question 17

L6
1) How does optical storage work?
2) How do you write data using optical storage?
3) How do you read data using optical storage?

Answer 17

1) How optical storage works:
- Optical storage devices use light to store data.
- A laser burns marks into the reflective surface of the disc.
- These marks are called pits and the gaps between them are called lands.
2) To write data, the discs spin and the laser burns the pits onto the reflective surface.
3) To read data, the disk rotates at a high speed. The laser head moves across the disk and the laser shines onto the disk. Tiny pits reflect light differently to the lands. Reflected light is interpreted into 1s and 0s representing data stored on the disk, and the data is stored on a single spiral track.

Question 18

L6
1) What are the 3 formats optical disks come in?
2) What are the advantages of optical storage?
3) What are the disadvantages of optical storage?

Answer 18

1) Optical discs come in three formats:
- Read-only (ROM)
- Write once (R)
- Rewritable (RW)
2) Advantages of optical storage:
- Cheap for small capacities
- Very small and portable
- Last a long time
3) Disadvantages of optical storage:
- Expensive for large capacities
- Easily scratched
- Slow read speeds
- Limited reusability

Question 19

L6
1) How does magnetic storage work?
2) How do you write data using magnetic storage?
3) How do you read data using magnetic storage?

Answer 19

1) Magnetic storage uses disks that spin at a high speed. There are read and write heads to read and write data; one for each side of the platter. Each platter is divided into sections, and data is organised in concentric rings called tracks.
2) To write data a set of discs called platters spin at a high speed and the read/write heads will magnetise and demagnetise tiny regions on the disk. The data is organised in concentric rings called tracks.
3) To read data the head moves over the spinning platters, measuring whether sections are magnetised or not.

Question 20

L6
1) What are the advantages of magnetic storage (state 4)?
2) What are the disadvantages of magnetic storage (state 3)?

Answer 20

1) Advantages of magnetic storage:
- Cheap for large capacities
- Infinitely rewritable
- Reliable for long periods of time
- Faster read speeds than optical
2) Disadvantages of magnetic storage:
- Damaged if dropped or exposed to a magnetic field
- Slower read speeds than solid state
- Require a lot of power to run

Question 21

L6
Compare these characteristics of storage devices:
1) Cost per GB
2) Capacity
3) Access speed

Answer 21

1) Solid-state is expensive, while magnetic and optical are both cheap.
2) Magnetic has a large capacity, solid state has a medium capacity and optical has a small capacity.
3) Solid-state is very fast, magnetic is slow and optical is very slow.

Question 22

L6
Compare these characteristics of storage devices:
1) Durability
2) Reliability
3) Portability

Answer 22

1) Solid-state is very robust as it has no moving parts, magnetic storage is robust, while optical storage is not as durable because they can be damaged easily by excessive sunlight or scratches.
2) Magnetic devices are very reliable, SSDs are reliable due to no moving parts, and optical devices can be damaged easily by excessive sunlight or scratches.
3) Optical is portable, solid state is portable, internal magnetic devices are not portable, but external magnetic devices are portable.

Question 23

L7
1) What is cloud storage?
2) How does cloud storage work?

Answer 23

1) A way to store and access files through the internet.
2) The data is stored on servers with hard drives. Cloud storage providers have warehouses full of these servers, called server farms.

Question 24

L7
1) What are the advantages of cloud storage?
2) What are the disadvantages of cloud storage?

Answer 24

1) Advantages of cloud storage:
Capacity can expand as you need it
Files can be accessed anywhere in the world, on any device
Sharing files is easier, enabling collaboration
Back-ups are easier, the provider looks after the files
2) Disadvantages:
Relies on an internet connection
Can still be slower than storing data on a physical device
Storing data online carries some risks

Question 25

L8
1) What are 2 ways the performance of a CPU core is effected?
2) What is a clock speed measured in?
3) What happens if the clock is pulsing quicker?
4) Explain what how the CPU performance is affected by more cache

Answer 25

1) The performance of a CPU core is effected by:
- Clock speed
- Cache size
2) Clock speed in measured in Hertz (Hz)
3) If the clock is pulsing quicker, the processor is able to complete more fetch-decode-execute cycles, and therefore increase the CPU speed.
4) Fetching data from catche is much faster than fetching data from RAM. If more instructions can be stored in cache, the processer will fetch data from RAM less frequently. Therefore, the processing speed would increase as the cache size gets bigger.

Question 26

L8
1) Explain how increasing the number of cores in the CPU will affect its speed
2) Explain how multiple cores share data, and the effect that this will have on the CPU

Answer 26

1) Each core can run its own fetch-decode-execute cycle, which increases the CPU speed.
2) In order to share data, the cores are connected by channels. Important data can be sent from one core to another.
This means that some of the clock pulses will be used to communicate between cores, slowing the processing speed.

Question 27

L9
1) Explain the AND logic gate
1) What is the boolean expression for the AND logic gate?
3) What is the symbol for the AND logic gate?

Answer 27

1) The binary logic for AND is that both inputs must be positive for a positive output.
2) The boolean expression for the AND logic gate is P = A.B
3) The symbol for the AND logic gate is a rectangle with a curved side at one end. It has 2 inputs on the flat side, and one output on the curved side.

Question 28

L9
1) Explain the NOT logic gate
2) What is the boolean expression for the NOT logic gate?
3) What is the symbol for the NOT logic gate?

Answer 28

1) The binary logic for NOT is that the output is not the input, ie. the input is inverted.
2) The boolean expression for the NOT logic gate is P = A with a straight line above the A
3) The symbol for the NOT logic gate is a triangle with a small circle attached at the corner end. There is one input on the flat triangle side, and one output at the circle end.

Question 29

L9
1) Explain the OR logic gate
1) What is the boolean expression for the OR logic gate?
3) What is the symbol for the OR logic gate?

Answer 29

1) The binary logic for OR is that at least one input must be positive for a positive output.
2) The boolean expression for the OR logic gate is P = A+B
3) The symbol for the OR logic gate is a triangle with curved sides. It has two inputs and one output. Remember the symbol as the gate’s curve forms the right of the letter O.

Question 30

L9
1) Explain the XOR logic gate
1) What is the boolean expression for the XOR logic gate?
3) What is the symbol for the XOR logic gate?

Answer 30

1) The binary logic for XOR or the exclusively OR gate is that it is only true when exactly one of the inputs are true.
2) The boolean expression for the XOR logic gate is P = A ⊕ B
3) The symbol for the XOR logic gate is a triangle with curved sides, and another curved line after the inputs. Remember the symbol as the gate’s curve forms the right of the letter O, and the extra curve is a cross through the middle of the O.

Question 31

L10
1) State the different types of programming languages
2) Explain the main differences between the two

Answer 31

1) There are different levels of programming language:
- low-level language
- high-level language
2) High-level languages require the use of a compiler or an interpreter for their translation into the machine code. Low-level language requires an assembler for directly translating the instructions of the machine language.

Question 32

L10
1) Explain why most programs are written using high level languages (state 9)
2) State the advantages and disadvantages of low-level language programming compared with high-level language programming (state 3)

Answer 32

1) - High-level languages have built-in functions
- High-level languages have built-in libraries
- High-level languages have more support
- High-level languages can be less machine dependent/more portable
- High-level lanugages usually requires fewer lines of code to be written
- Usually quicker to develop code in high-level languages
- It is easier to find mistakes in code
- The code is easier to understand and maintain
- It is easier to structure code in high-level languages
2) Programs written in assembly or machine code run faster, programs require less memory when executing and programs written in assembly language have no extra code added by the computer.

Question 33

L11
1) What are the two types of low level languages?
2) What are the differences between the two types of low level languages?
3) Describe what assembly language is used for
4) What kind of code is executed by the processor?

Answer 33

1) Machine code and assembly language are low-level languages.
2) Machine code is a low level language that is directly understood by the CPU, and is written in binary. It is specific to a processor or family of processors.
3) Assembly language is often used to develop software for embedded systems and for controlling specific hardware components. Assembly language has a 1:1 correspondence with machine code.
4) Processors execute machine code. Each type of processor has its own specific machine code instruction set.
All programming code written in high-level or assembly languages must be translated.

Question 34

L11
1) State the different types of programming languages
2) State the three common types of program translator
3) Explain the main differences between these three types of translator

Answer 34

1) There are different levels of
programming language:
- low-level language
- high-level language
2) There are three common types of program translator:
- Interpreter
- Compiler
- Assembler
3) A compiler translates high level programming languages into machine code. It translates all the code in one go.
An assembler translates assembly languages into machine code, and each line of assembly language is assembled into a single machine code instruction.
An interpreter translates high level programming languages into machine code. An interpreter translates source code into machine code one instruction at a time. The resulting machine code is then executed immediately. Interpreters do not produce any machine code so the program needs to be translated each time it is executed. They call machine code subroutines within their own code to carry out commands and directly execute the instruction. If a runtime error is found the interpreter stops.

Question 35

What is the function of the following registers:
1) Current instruction register (CIR)
2) Memory address register (MAR)
3) Memory data register (MDR)

Answer 35

1) Current instruction register (CIR): Holds the current instruction that the processor is executing
2) Memory address register (MAR): Temporarily stores the memory addresses used when searching for data in RAM
3) Memory data register (MDR): Temporarily holds the data (data values or instructions) that are read from or written to the main memory

Question 36

What is the function of the following registers:
1) Program counter (PC)
2) accumulator (ACC)

Answer 36

1) Program counter (PC): Holds the address of the next instruction to be executed by the processor
2) Accumulator (AC): Stores the result of any calculation

Question 37

Describe the functions performed by the operating system (state 5)

Answer 37

• Memory management: it manages the computer’s memory, and can control which parts of memory are being used by which process.
• Input/ output management: it manages input/ output devices, controls network communication and allows devices to send and receive data.
• Managing storage: it manages secondary storage devices, manages loading data and programs into the computer’s memory and manages storage space.
• Managing security: it manages user authentication, protects against malware, and blocks access to specific vulnerable operations or system areas (such as installing software).
• Managing applications: it controls access to applications and prevents users or processes from using unauthorised programs.

Question 38

L8
1) What is main memory?
2) Explain how main memory is used?

Answer 38

1) Main memory is any form of memory that is directly accessible by the CPU, except for cache and registers.
2) It stores instructions whilst a program is being executed. The CPU fetches instructions from main memory to decode, and stores the results of the execution of the instructions in the main memory.

Question 39

1) What is hardware?
2) What is software?

Answer 39

1) Hardware is the physical components of a computer system.
2) Software is the programs, code or instructions that are executed by the hardware.

Question 40

1) Explain why secondary storage is required in a computer system
2) State 3 examples of volatile memory in a computer system

Answer 40

1) Secondary storage stores all the user’s files, applications and operating systems. Secondary storage is needed to store data or files when the computer is switched off on a long term basis.
2) RAM, cache and registers