Unit 1: Digital Technology – Computer Hardware Study Notes
Welcome to the study notes for Computer Hardware! Hardware refers to all the physical, touchable components of a computer system. Whether it is the processor running billions of calculations per second or the hard drive storing your favourite photos, understanding how hardware works is essential for your CCEA GCSE Digital Technology exam.
Don't worry if some of the technical terms feel unfamiliar at first. We will break down every single concept step-by-step with real-world examples, clear definitions, and helpful revision tips.
---1. The Central Processing Unit (CPU)
The Central Processing Unit (CPU) is the core component of any computer system. Its main role is to coordinate and execute all instructions and manage the hardware operations across the entire system.
Main Components of the CPU
Inside the CPU, three main internal parts work together:
• Control Unit (CU): The CU directs and coordinates all hardware operations. It manages the flow of data through the CPU, issues control signals to other components, and manages instruction execution.
• Arithmetic and Logic Unit (ALU): The ALU performs two types of operations:
1. Arithmetic calculations: Performing mathematical calculations such as addition and subtraction.
2. Logical decisions: Carrying out logical comparisons like AND, OR, NOT, greater than, and less than.
• Immediate Access Store (IAS) / Internal Registers: These are extremely fast, temporary storage locations built directly within or adjacent to the CPU:
1. Program Counter (PC): A register that holds the memory address of the next instruction waiting to be fetched. It automatically increments by 1 after each fetch.
2. Memory Data Register (MDR): A register that temporarily holds the actual data or instruction fetched from, or waiting to be written to, main memory (RAM).
3. Cache Memory: High-speed volatile memory situated directly on or very close to the CPU chip. It stores frequently accessed instructions and data so the CPU does not have to waste time waiting for slower RAM.
The Fetch–Decode–Execute (F-D-E) Cycle
To run any program, the CPU continuously carries out a three-step cycle:
1. Fetch: The next instruction is retrieved from main memory (RAM) into the CPU registers (using addresses held by the Program Counter and transferred via the Memory Data Register).
2. Decode: The Control Unit (CU) interprets the instruction to work out what action is required.
3. Execute: The instruction is carried out. This might involve an arithmetic calculation or logical test in the ALU, moving data between registers, or performing an input/output operation.
Factors Affecting CPU Performance
Not all processors perform at the same speed. Three major hardware factors determine how fast a CPU can process instructions:
• Clock Speed: The internal clock produces regular electrical pulses to synchronise operations. Clock speed is measured in Hertz, typically Gigahertz (\(\text{GHz}\)). For example, a \(3.2\text{ GHz}\) CPU performs \(3.2\text{ billion cycles per second}\). The higher the clock speed, the more instructions can be executed every second.
• Number of Cores: A core is an independent processing unit within the CPU chip. A processor can have a single core, dual cores (2), quad cores (4), or octa-cores (8). Multiple cores allow simultaneous execution of parallel instructions, which improves multitasking and multiprocessing.
• Cache Size: A larger cache (such as \(6\text{ MB}\) to \(12\text{ MB}\)) allows more frequently used instructions and data to stay on the high-speed CPU die, drastically reducing the time spent fetching data from slower RAM.
Examiner Tip: When asked why a computer runs faster, never mention just clock speed alone! High-scoring answers discuss a combination of clock speed, cache size, number of CPU cores, and available RAM.
Key Takeaway: The CPU executes instructions using the Fetch–Decode–Execute cycle. The Control Unit directs operations, the ALU handles maths and logic, and registers like the PC and MDR hold temporary data and addresses.
---2. Primary Memory: RAM vs ROM
Primary memory is directly accessible by the CPU. There are two essential types of primary memory: RAM and ROM.
Random Access Memory (RAM)
• Function: Serves as temporary (working) storage that holds programs, open files, and operating system modules that are currently in use.
• Characteristics: Volatile (all data is lost immediately when power is turned off). It has Read/Write capability, meaning the CPU can both read data from it and write new data to it.
Read-Only Memory (ROM)
• Function: Permanent storage holding the essential startup instructions needed to boot the computer (including the firmware, BIOS, bootstrap loader, and POST - Power-On Self-Test).
• Characteristics: Non-volatile (contents are permanently retained even when power is disconnected). It is Read-only, meaning contents are written during manufacturing and cannot be easily altered or overwritten.
Everyday Analogy: Think of RAM like the top of your study desk—you lay out the books you are actively using right now. When you leave and turn off the light, the desk is cleared. ROM is like a printed instruction manual glued inside a drawer—it contains permanent instructions on how to set up the desk and never disappears.
Common Mistake to Avoid: Never confuse RAM with your computer's storage drive (SSD or Hard Drive). When you click 'Save', files move from temporary RAM to permanent secondary storage.
Key Takeaway: RAM is volatile read/write memory for currently running programs; ROM is non-volatile read-only memory holding startup/boot instructions.
---3. Secondary Storage Technologies
Because RAM is volatile, computers require Secondary Storage to permanently save user files, software applications, and the operating system when the power is turned off.
1. Magnetic Storage
• How it works: Uses mechanical rotating platters coated in magnetic material. Read/write heads move across the surface and magnetise tiny areas with positive or negative polarity to represent binary \(0\) and \(1\).
• Examples: Hard Disk Drives (HDD), Magnetic Tape.
• Advantages: Very large storage capacities (measured in Terabytes); low cost per gigabyte.
• Disadvantages: Contains moving mechanical parts that can fail if dropped or knocked; slower read/write speeds than SSDs; data can become fragmented over time.
2. Solid-State / Flash Memory
• How it works: Uses non-volatile NAND flash memory chips consisting of floating-gate and control-gate transistors. There are zero moving parts.
• Examples: Solid-State Drives (SSD), USB Flash Drives, SD / microSD cards.
• Advantages: Extremely fast read/write access speeds; highly durable and shock-resistant; silent in operation; lightweight with low power consumption.
• Disadvantages: More expensive per gigabyte compared to HDDs; has a finite number of write cycles over its lifetime.
3. Optical Storage
• How it works: A laser beam shines on a spinning disc to read microscopic pits and lands etched along a continuous spiral track on a reflective layer.
• Examples and Capacities:
- CD-ROM / CD-R / CD-RW: Approximately \(700\text{ MB}\)
- DVD: Approximately \(4.7\text{ GB}\)
- Blu-ray: Approximately \(25\text{--}50\text{ GB}\)
• Advantages: Highly portable; very low cost per disc; ideal for physical media distribution.
• Disadvantages: Slower read/write speeds; lower storage capacity compared to HDDs and SSDs; discs are easily scratched or damaged by sunlight.
Key Takeaway: Magnetic storage offers high capacity at low cost, solid-state is fast and durable with no moving parts, and optical storage is cheap and portable for disc media.
---4. Input and Output Devices
Peripherals allow users and external systems to communicate with the computer by inputting data or receiving processed output.
Input Devices (Data Capture)
Input devices capture data and convert it into a digital format for the CPU to process.
• Manual Input Devices: Require direct human action.
- Keyboard: For entering text and numeric commands.
- Mouse / Pointing Device: For navigating graphical user interfaces.
- Touchscreen: Dual-purpose device allowing direct touch selection.
- Microphone: Captures audio waves (requires an Analogue-to-Digital Converter / ADC for processing and voice recognition).
• Automated / Dedicated Input Devices: Capture data automatically with minimal human intervention.
- Barcode Scanner: Reads reflected light from printed barcodes, commonly used at Point-of-Sale (POS) checkouts.
- RFID Reader: Uses radio waves to read data stored on RFID tags wirelessly.
- Magnetic Stripe Reader: Reads magnetic patterns on the back of cards (e.g., membership cards).
- OCR (Optical Character Recognition): Scans printed text and converts it into editable digital text.
- OMR (Optical Mark Recognition): Detects marked boxes on paper forms (e.g., lottery tickets or multiple-choice exam sheets).
- Sensors: Continuously capture physical environmental data such as temperature, light, pressure, or motion.
Output Devices
Output devices present processed data to humans or control physical mechanisms.
• Visual / Display Outputs:
- Monitors / Screens: Use LCD, LED, or OLED technology to display visual interfaces and content.
- Projectors: Display large-format computer output onto walls or screens.
• Hardcopy Outputs:
- Laser Printers: Produce fast, high-volume documents with a low cost per page using toner.
- Inkjet Printers: Produce high-quality photo prints using liquid ink cartridges, but are slower and have a higher ongoing ink cost.
- Plotters: Produce high-precision architectural and engineering drawings.
- 3D Printers: Build physical three-dimensional objects layer by layer from digital models.
• Audio and Actuation Outputs:
- Speakers and Headphones: Output audio signals as sound waves.
- Actuators / Motors: Produce physical movement (e.g., opening automated doors, moving robotic limbs, or controlling valves).
Key Takeaway: Input devices capture data manually or automatically (sensors, scanners), while output devices present information visually, on paper (printers), as audio, or via physical movement (actuators).
---Quick Exam Revision Checklist
Before your exam, make sure you can confidently:
• Explain the role of the CU, ALU, PC, MDR, and Cache in the CPU.
• Describe the three stages of the Fetch–Decode–Execute Cycle.
• State how Clock Speed (\(\text{GHz}\)), Cores, and Cache Size impact CPU performance.
• Contrast RAM (volatile, read/write) with ROM (non-volatile, read-only startup instructions).
• Compare Magnetic, Solid-State, and Optical storage in terms of speed, capacity, durability, and cost.
• Identify appropriate manual/automated input devices and output devices for given real-world scenarios.