Cambridge AS & A Level9608

Hardware

Computer Science 9608 Chapter Notes

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Hardware
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In this chapter

  1. 1Computer Hardware and Von Neumann Architecture
  2. 2Input Devices: Capturing Data
  3. 3Output Devices: Presenting Information
  4. 4Primary Storage: RAM, ROM, and Cache
  5. 5Secondary and Offline Storage

1. Computer Hardware and Von Neumann Architecture

Hardware refers to the physical components of a computer system that you can touch. These are broadly categorized into input, output, processing, and storage devices. The fundamental design of most modern computers is based on the Von Neumann architecture. This model proposes that both program instructions and the data the program uses are stored in the same memory. A central processing unit (CPU) fetches these instructions and data from memory, executes the instructions, and stores the results back in memory. The main components are the CPU, main memory, and input/output (I/O) devices, all connected by buses.

Key term

Von Neumann Architecture: A computer architecture model where program instructions and data are stored in the same memory location and can be accessed by a single processor.

Examiner insight

Examiners often ask for a diagram of the Von Neumann architecture. Be prepared to draw and label the processor, memory, and the buses connecting them.

Common pitfall

Students often forget to mention that both data and instructions are stored in the same memory, which is a key feature of the Von Neumann model.

Worked example 15 marks

Describe the Von Neumann architecture, mentioning its key components and their basic function.

  1. 1
    1. The Von Neumann architecture is a model for computer design that uses a single storage unit (main memory) for both program instructions and data.
  2. 2
    1. It has three main components: The Central Processing Unit (CPU), Main Memory, and Input/Output (I/O) devices.
  3. 3
    1. The CPU is the 'brain' of the computer. It fetches instructions from memory, decodes them, and executes them. It consists of the Arithmetic Logic Unit (ALU) and the Control Unit (CU).
  4. 4
    1. Main Memory (like RAM) stores the operating system, currently running applications, and the data they are processing. It is directly accessible by the CPU.
  5. 5
    1. I/O devices allow the computer to interact with the outside world. Input devices (e.g., keyboard) send data to the computer, and output devices (e.g., monitor) receive data from it.
  6. 6
    1. These components are connected by system buses: the Address Bus carries memory addresses, the Data Bus carries data, and the Control Bus carries command and timing signals.

Recap

  • Hardware refers to the physical parts of a computer.
  • The Von Neumann architecture is the basis for most modern computers.
  • It features a single memory for both instructions and data.
  • The key components are the CPU, Main Memory, and I/O devices.
  • Components are connected via the system bus (Address, Data, and Control buses).

Quick check

  1. What are the two types of information stored in main memory in a Von Neumann architecture?2 marks

2. Input Devices: Capturing Data

Input devices are hardware components that allow users to send data and control signals to a computer. They convert real-world actions, images, or sounds into a digital format that the computer can process. Common examples include keyboards for text entry, mice for navigation, scanners for digitising documents, and microphones for capturing audio. The choice of input device depends entirely on the type of data being captured and the context of its use.

Key term

Sensor: A device that detects a physical property (like light, heat, or pressure) and converts it into an electrical signal that a computer can interpret.

Examiner insight

For questions about input devices, focus on the application. Don't just name a device; explain *why* it is suitable for a given scenario, mentioning properties like speed, accuracy, or ease of use.

Worked example 14 marks

A public library wants to upgrade its book check-out system to be faster and more accurate. Suggest and justify two different input devices that could be used.

  1. 1
    1. Device 1: Barcode Reader. Each book would have a unique barcode. The librarian can scan the book's barcode to quickly and accurately identify it in the system's database. This is much faster and less error-prone than manually typing in a book ID number.
  2. 2
    1. Justification for Barcode Reader: It provides high speed, excellent accuracy, and is a low-cost, durable technology that staff can be trained to use very easily.
  3. 3
    1. Device 2: Capacitive Touchscreen Monitor. This could be used by the librarian to navigate the lending software, or as a self-service kiosk for library members. Users can tap on-screen options to look up, borrow, or return books.
  4. 4
    1. Justification for Touchscreen: It provides an intuitive and fast user interface, removing the need for a separate mouse and keyboard, which saves counter space and can be easier for the public to use.

Worked example 24 marks

Explain the basic principle of how a 2D flatbed scanner works.

  1. 1
    1. A 2D flatbed scanner is used to convert a physical document or image into a digital file.
  2. 2
    1. The document is placed face-down on a glass plate. A bright light (often an LED bar) illuminates the document.
  3. 3
    1. A scan head, containing a series of mirrors and a lens, moves beneath the glass. It focuses the reflected light from the document onto a light-sensitive sensor.
  4. 4
    1. This sensor is typically a Charge-Coupled Device (CCD) or Contact Image Sensor (CIS). The sensor converts the light intensity and colour for each tiny area (pixel) of the document into an electrical signal.
  5. 5
    1. An Analogue-to-Digital Converter (ADC) then converts these analogue electrical signals into digital values, which are assembled by software to form the final digital image.

Recap

  • Input devices feed data into a computer system.
  • Keyboards, mice, scanners, and microphones are common input devices.
  • Sensors are a special type of input device that measure physical quantities.
  • The choice of input device is determined by the specific application and data type.
  • Many input devices use an Analogue-to-Digital Converter (ADC) to digitise real-world data.

Quick check

  1. What is the primary difference in operation between a resistive and a capacitive touchscreen?2 marks

3. Output Devices: Presenting Information

Output devices are hardware components that convey information from the computer to a user or another system. They translate the computer's digital data into a human-understandable form, such as text, graphics, sound, or physical movement. The most common output devices are monitors for visual display and printers for physical copies. Other examples include speakers, projectors, and actuators in control systems.

Key term

Actuator: A component of a machine that is responsible for moving or controlling a mechanism or system, converting a control signal into physical action.

Common pitfall

Confusing LCD and LED monitors. An 'LED monitor' is an LCD monitor that uses LEDs for its backlight. The underlying display technology is still Liquid Crystal Display.

Fun fact

The pixels in an OLED display generate their own light. This is why OLED screens can display 'perfect' black (by simply turning the pixels off completely) and have very high contrast ratios.

Worked example 16 marks

A small business needs to buy a new printer. They print about 50 pages of black-and-white text documents per day, but occasionally need to print high-quality colour marketing flyers. Compare a laser printer and an inkjet printer for this scenario.

  1. 1
    1. Laser Printer Operation: Uses powdered toner and heat. A laser beam draws an electrostatic image on a rotating drum. Toner sticks to the charged areas, is transferred to the paper, and fused on by heat. It is very fast for text.
  2. 2
    1. Inkjet Printer Operation: Sprays microscopic droplets of liquid ink onto the paper from a moving print head. It is generally better for high-resolution colour photo and image printing.
  3. 3
    1. Cost: A laser printer usually has a higher initial purchase price but a lower cost per page for black-and-white text, as toner cartridges print thousands of pages. An inkjet printer is cheaper to buy but ink cartridges can be expensive and print fewer pages, making the cost per page higher.
  4. 4
    1. Recommendation: For this business, a colour laser printer would be the best investment. While the initial cost is higher, the low cost per page for their daily text documents will save money in the long run. Modern colour laser printers also produce very good quality marketing materials, suitable for flyers.

Recap

  • Output devices present processed data to the user.
  • Monitors (LCD, LED, OLED) provide visual output.
  • Printers (Inkjet, Laser, 3D) produce hard copies.
  • Speakers and headphones produce audio output via a Digital-to-Analogue Converter (DAC).
  • Actuators are output devices that produce physical movement in control systems.

Quick check

  1. What do the acronyms LCD and LED stand for in the context of computer monitors?2 marks

4. Primary Storage: RAM, ROM, and Cache

Primary storage, also known as main memory, is the memory that the CPU can access directly. It is volatile and holds the data and instructions that the computer is currently working on. It is much faster than secondary storage. There are three main types: RAM, ROM, and Cache.

  • RAM (Random Access Memory): This is the main workspace of the computer. It is volatile (loses content when power is off) and is used to store the operating system, running applications, and the data currently in use.
  • ROM (Read-Only Memory): This is non-volatile (keeps content when power is off). It contains the instructions needed to start the computer, known as the bootstrap program or BIOS/UEFI. As the name suggests, its contents cannot normally be changed by the user.
  • Cache Memory: A very small, extremely fast, and expensive type of memory (SRAM) located on or very close to the CPU. It stores copies of frequently used instructions and data from RAM, so the CPU can access them much faster than fetching them from RAM again.

Key term

Volatility: A characteristic of memory that describes whether it retains its contents when power is removed; volatile memory loses its data, while non-volatile memory keeps it.

Common pitfall

Mixing up RAM and ROM. Remember: ROM is for *starting* the computer (Read-Only), RAM is for *running* programs (it's the computer's 'working area').

Worked example 15 marks

Explain the role of RAM, ROM and Cache memory when a computer is first switched on and the user opens a word processing application.

  1. 1
    1. When the computer is switched on, the CPU begins executing instructions stored in ROM. This is the non-volatile memory containing the bootstrap loader.
  2. 2
    1. The bootstrap program performs initial hardware checks (POST) and then loads the main operating system (e.g., Windows) from the secondary storage (e.g., SSD) into RAM.
  3. 3
    1. Once the OS is loaded into RAM, the CPU can run it. The user can now interact with the OS.
  4. 4
    1. When the user clicks to open the word processor, the OS finds the application on the secondary storage and copies its program files into a free section of RAM.
  5. 5
    1. As the CPU executes the word processor's instructions, it copies the most frequently used instructions and data from the slower RAM into the much faster Cache memory. This speeds up future access to that same data, improving performance.

Recap

  • Primary storage is directly accessible by the CPU.
  • RAM is volatile memory used for currently running programs and data.
  • ROM is non-volatile memory used to boot the computer.
  • Cache is a small, very fast volatile memory that stores frequently accessed data to speed up CPU operations.
  • There is a trade-off between speed, capacity, and cost: Cache is fastest but smallest, RAM is in the middle, and secondary storage is slowest but largest.

Quick check

  1. Is RAM volatile or non-volatile? What about ROM?2 marks

5. Secondary and Offline Storage

Secondary storage is non-volatile memory that is not directly accessible by the CPU. It is used for long-term storage of the operating system, applications, and user files. It is slower than primary storage but has a much larger capacity and is cheaper per gigabyte. We can classify secondary storage by its underlying technology:

  • Magnetic Storage: Uses magnetic patterns to represent data on a spinning platter. The main example is the Hard Disk Drive (HDD). They offer high capacity at a low cost but have moving parts, making them slower and less durable than SSDs.
  • Optical Storage: Uses a laser to read and write data from a spinning disc in the form of microscopic pits and lands. Examples include CDs, DVDs, and Blu-Ray discs. They are cheap and portable but have limited capacity and slow access speeds.
  • Solid-State Storage: Uses non-volatile flash memory (NAND chips) to store data with no moving parts. Examples are Solid-State Drives (SSDs), USB flash drives, and SD cards. They are very fast, durable, and portable, but are more expensive per gigabyte than HDDs.

Key term

Solid-State Drive (SSD): A secondary storage device that uses non-volatile flash memory to store data persistently, offering much faster access times than a traditional hard disk drive.

Examiner insight

Comparison questions are very common. Be prepared to compare two or three storage types on specific criteria like speed, portability, and cost. Use comparative language like 'faster than', 'more portable than', or 'cheaper per gigabyte'.

Worked example 15 marks

A student needs to back up their important coursework (around 10 GB of files) and store it safely at home. They are considering a Blu-Ray disc, a USB flash drive, or an external HDD. Justify which one would be the most suitable choice.

  1. 1
    1. Candidate 1: Blu-Ray Disc. A standard Blu-Ray can hold 25GB, which is sufficient. It is cheap and has a long shelf-life if stored correctly. However, it requires a Blu-Ray writer, is slow to write data to, and is a read-once medium (BD-R), making it inflexible for regular updates.
  2. 2
    1. Candidate 2: External HDD. An external Hard Disk Drive would offer a huge capacity (e.g., 1TB or more) for a relatively low price. However, it has moving parts, making it fragile and susceptible to damage if dropped. It is also larger and requires a cable.
  3. 3
    1. Candidate 3: USB Flash Drive. A 16GB or 32GB flash drive has enough capacity. It is small, highly portable, and durable due to having no moving parts. It is also very easy to use (plug-and-play) and allows files to be easily added, deleted, and modified.
  4. 4
    1. Conclusion & Justification: The USB flash drive is the most suitable choice. It provides sufficient capacity, is more durable and portable than an HDD, and is more flexible and convenient for regular backups than a Blu-Ray disc.

Recap

  • Secondary storage is non-volatile and used for long-term data storage.
  • Magnetic storage (HDD) offers high capacity at a low cost.
  • Optical storage (CD/DVD/Blu-Ray) is cheap and used for distribution and archiving.
  • Solid-state storage (SSD, USB drive) is fast, durable, and has no moving parts.
  • Storage devices are compared based on capacity, speed, portability, durability, and cost.

Quick check

  1. Give one advantage and one disadvantage of an SSD compared to an HDD.2 marks

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. Define the term 'hardware' and give one example of an input device and one example of an output device.3 marks
  2. State two differences between RAM (Random Access Memory) and ROM (Read-Only Memory).2 marks
  3. Explain the principle of operation for a capacitive touchscreen.3 marks
  4. A professional video editor works with very large files (often over 100GB). They need fast access to their current projects and a separate solution for long-term archiving of completed work. Recommend and justify a primary secondary storage device for their computer and a separate device for archiving.5 marks
  5. Describe the roles of the CPU, RAM, and a secondary storage device when a user launches a web browser on their computer.4 marks
  6. Compare and contrast a laser printer and an inkjet printer in terms of their printing mechanism, speed, and typical running costs.6 marks
  7. Explain why a computer system has a memory hierarchy (cache, RAM, secondary storage) instead of just using one single type of storage.4 marks
  8. A modern supermarket is designing a new self-service checkout counter. Describe three essential hardware components (one input, one output, and one storage) for this counter. Justify your choice for each component.6 marks
  9. Draw a simple, labelled block diagram of the Von Neumann architecture. Briefly explain the function of the system bus in your diagram.5 marks
  10. Explain the difference between a monitoring system and a control system, giving an example of a sensor and an actuator that might be used in an automated greenhouse.4 marks

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