Chapter 3.1: Hardware, Storage, I/O Devices & Monitoring/Control Systems
9618 AS Computer Science
📚 Learning Objectives
Show understanding of need for primary memory, secondary storage
Describe principal operations of hardware devices (HDD, SSD, optical disc)
Explain differences between RAM and ROM, SRAM and DRAM
Explain differences between PROM, EPROM and EEPROM
Show understanding of embedded systems, benefits and drawbacks
Show understanding of input/output devices and their operations
Show understanding of monitoring and control systems
Understand the use of sensors, actuators, and feedback loops
🌟 Did You Know?
A computer system must support three major operational capabilities: Storage of Data, Processing of Data (by CPU), and Input/Output of Data. Storage devices are integral to computer hardware - without them, a computer would not be able to run or even boot up!
1. Primary Memory
Primary memory is part of computer memory which can be accessed directly from the CPU. Primary memory is used to store data, files, parts of an application or parts of the operating system currently in use. It has much faster access times than secondary storage, which speeds up operations like the Fetch-Execute Cycle.
1.1 Random Access Memory (RAM)
RAM is the primary storage directly connected to the CPU that holds data and instructions currently in use. It is volatile memory, meaning contents are lost when power is turned off.
📖 Key Characteristics of RAM
It is read-write memory - can be read from or written to any number of times
Called "Random Access" because any byte can be accessed without affecting other bytes
Also called direct-access memory
Used to hold data and programs currently in use
Larger RAM = faster computer operation
1.2 Types of RAM: DRAM vs SRAM
Feature
DRAM (Dynamic RAM)
SRAM (Static RAM)
Construction
Uses transistors and capacitors
Uses flip-flops to hold each bit
Refreshing
Needs constant refreshing
No refreshing required
Speed
Slower access time
Faster access time
Cost
Less expensive to manufacture
More expensive
Capacity
Higher memory capacity
Lower capacity per chip
Power
Consumes more power (refresh cycles)
Less power under normal use
Usage
Main memory in computers
Processor cache memory
💡 Exam Tip
Remember: DRAM = Dynamic = Needs Refreshing (like a dynamic person who needs constant attention), while SRAM = Static = Stable (holds data without refreshing). SRAM is faster but more expensive, so it's used for cache where speed is critical.
2. Read Only Memory (ROM)
ROM is primary storage that holds the first instructions a computer needs to start up (Bootstrap/BIOS). Unlike RAM, ROM is non-volatile - contents are not lost when power is turned off.
📖 Key Characteristics of ROM
Non-volatile - contents retained after powering off
Permanent memory - contents cannot be easily changed
Stores BIOS (Basic Input Output System)
Stores bootstrap program for system startup
Faster than secondary storage but slower than RAM
Read only - data can only be read, not written
2.1 Types of ROM
📝 Types of Programmable ROM
1. PROM (Programmable ROM):
Can be altered once only
Manufacturer supplies chips to system builder
Uses matrix of fuses - programming "burns" fuses
Used in mobile phones, RFID tags
2. EPROM (Erasable PROM):
Can be re-written using ultra-violet light multiple times
Must be removed from device to erase/rewrite
Entire chip must be erased before rewriting
Used in applications under development (e.g., new game consoles)
3. EEPROM (Electrically Erasable PROM):
Re-written and erased using electric voltage
Can remain in circuit while contents are changed
Specific bytes can be erased (not entire chip)
Used in BIOS chips, smart cards, USB flash drives, SSDs
2.2 RAM vs ROM Comparison
Feature
RAM
ROM
Memory Type
Temporary memory device
Permanent memory device
Volatility
Volatile (lost when power off)
Non-volatile
Read/Write
Both read and write
Read only
Contents
Data, programs, OS currently in use
BIOS, bootstrap instructions
Capacity
Gigabytes (GB)
Megabytes (MB)
Speed
Very fast
Fast (slower than RAM)
3. Secondary Storage Devices
Secondary storage includes storage devices that are not directly accessible by the CPU. They are non-volatile devices which allow data to be stored permanently. All applications, operating system, device drivers, and files are stored on secondary storage.
📖 Three Categories of Secondary Storage
Magnetic Storage: Internal/External Hard Disks
Solid State: SSDs, USB Flash Drives
Optical Storage: CD, DVD, Blu-ray discs
3.1 Magnetic Hard Disk Drives (HDD)
Data is stored in digital format on magnetic surfaces of disks called platters. A hard disk drive will have multiple platters, each with two surfaces for storing data.
📝 How HDD Works
Platters spin in unison at high speed (5400-7200 RPM)
Read-write heads access all surfaces; attached to actuator arms
A cushion of air ensures heads don't touch platter surfaces
Data stored in sectors and tracks
Each sector contains a fixed number of bytes
⚠️ Important: Latency & Fragmentation
Latency: Time taken for a block in a sector to rotate to the read-write head. Many applications require constant head movements, making latency significant.
Fragmentation: Through deletions and editing, sectors become fragmented, causing gradual performance decline. Defragmentation software can improve performance by "tidying up" disk sectors.
HDD Characteristic
Description
Storage Method
Magnetised particles on platters (0s and 1s)
Organization
Concentric tracks divided into wedge-shaped sectors
Access Type
Direct access device; data in sector read sequentially
Advantages
High capacity, low cost per GB, reliable
Disadvantages
Slower than SSD, moving parts can wear out
4. Solid State Drives (SSD) & Optical Storage
4.1 Solid State Drives
SSDs have no moving parts and all data is retrieved at the same rate. Data is stored as 0s and 1s in millions of tiny transistors within chips using NAND or NOR flash memory technology.
📖 How Data is Stored in Flash Memory
Data recorded in transistors called Floating Gates
NAND-based memory: Reads faster than writes; access by blocks; used in SSDs, USB drives, memory cards
NOR-based memory: More expensive, slower but longer life; bit-level access; used in computer ROM (EEPROM technology)
Control Gate: Controls charge flow from Source to Drain
SSD Benefits
SSD Drawbacks
More reliable (no moving parts)
Limited write endurance (~20GB/day for 3 years)
Considerably lighter (ideal for laptops)
Higher cost per GB
Lower power consumption
Not ideal for servers with many write operations
Run cooler than HDDs
Data recovery more difficult
Very thin design
Much faster data access
4.2 Optical Storage Media
CDs, DVDs, and Blu-rays use laser light to read and write data. Data is stored in pits and lands on a spiral track running from center to edge.
📝 How Optical Media Works
Lands (bumps): Reflect laser light → Binary '1'
Pits: Scatter laser beam → Binary '0'
DVD vs CD: DVDs use dual layering, smaller pits, narrower tracks, and shorter wavelength laser (650nm vs 780nm)
Blu-ray: Uses blue laser (405nm wavelength), allowing smaller pits and up to 5x more storage than DVD
💡 Exam Tip
Remember the relationship: Shorter wavelength = Smaller pits = Greater storage capacity. That's why Blu-ray (405nm blue laser) stores more than DVD (650nm red laser), which stores more than CD (780nm red laser).
5. Output Devices
Output devices are hardware components that receive information from a computer and present it to the user. They enable the computer to communicate processed data or commands.
5.1 Laser Printers
Laser printers are non-impact page printers that use dry powder ink (toner) and static electricity to produce text and images. They print a whole page at once.
📝 Laser Printer Operation
Data sent to printer driver, then stored in printer buffer
Drum given electric charge, starts revolving step by step
Laser beam directed across drum - either switched on (discharge) or off (leave charge)
Charged toner coats drum, sticking only to discharged positions
Drum rolls over charged paper, transferring toner
Paper passes through heated rollers to fuse toner onto surface
Drum discharged before next page cycle
5.2 Inkjet Printers
Inkjet printers are non-impact line printers that produce good quality color prints by firing droplets of ink through nozzles onto paper.
📖 Inkjet Printer Components
Print Head: Contains nozzles that fire ink droplets; moves horizontally across paper
Ink Cartridges: One for each color (cyan, yellow, magenta) plus black
Stepper Motors: Move print head (via belt), park print head, and feed paper
Paper Feed: Automatically supplies pages as required
5.3 3D Printers
3D printers generate three-dimensional physical objects from digital files using additive manufacturing - building up layer by layer.
Device
Principal Operation
Use Case
Speakers
Convert electrical signals to sound waves via diaphragm movement in magnetic field
Audio output, voice commands, multimedia
VR Headset
Creates immersive 360° environment using head tracking, motion sensors, stereoscopic displays
Gaming, training, design, therapy
Plotter
Uses pens to draw vector graphics on large paper; sprockets move paper, pens draw
Architecture, engineering designs
6. Input Devices
Input devices are hardware components that allow users to input data or commands into a computer system for processing.
6.1 Touchscreens
Touchscreens work as both input and output devices - you view options (output) and touch to select (input).
Type
How It Works
Application
Capacitive
Multiple glass layers act as capacitors; touch changes electric field; coordinates detected by microprocessor
Smartphones, tablets
Infra-Red (Heat)
Glass screen; needs warm object (finger) for input
Microphones convert sound waves into electrical signals that can be processed by the computer.
📝 How Microphones Work
Sound causes air to vibrate
Diaphragm in microphone picks up vibrations
Copper coil wrapped around magnet moves with diaphragm
Movement creates electric current (electromagnetic effect)
Current digitized by ADC in sound card, sent to computer
6.3 Other Input Devices
Device
Function
Scanner
Creates digital representation of images; light source moves across paper; reflected light directed to CCD
Webcam
Streams video images into computer system
Digital Camera
Captures images/video for download to computer
Barcode Reader
Scans barcodes for retail and inventory management
Graphics Tablet
Allows artists to draw/sketch directly into computer
7. Embedded Systems
An embedded system is a computer system used to perform a dedicated function inside a larger mechanical unit. It involves installing microprocessors into devices to enable operations to be controlled more efficiently.
📖 Features of Embedded Systems
Dedicated to a single task or limited number of functions
Built into/integrated into a larger system
Must contain: processor, memory, and I/O capability
Often no requirement for an operating system
Can be activated by web-enabled devices (e.g., mobile phone apps)
Examples: Heating thermostats, hospital equipment, washing machines, dishwashers, coffee machines, satellite navigation, factory equipment, security systems, traffic lights, lane detection systems in cars.
Benefits
Drawbacks
Small and compact - easy to fit into devices
Limited functionality - only performs specific tasks
Low power consumption - efficient
Hard to upgrade or repair - often built into device
Fast and reliable - designed for quick, repetitive tasks
Limited memory and processing power
Cheaper to produce - minimal hardware
Not flexible - can't easily be reprogrammed
Works in real-time - ideal for time-sensitive operations
May be less secure if connected to other systems
💡 Exam Tip
When asked why something is an embedded system, mention: (1) It is built into/integrated into the device, (2) It performs a specific/dedicated task, (3) It is not easily changed or updated by the user.
7.1 EEPROM in Embedded Systems
Embedded systems often use EEPROM because:
No additional equipment needed to change contents
Enables firmware updates by non-technical users
Can be erased and reprogrammed several times
Can erase specific bytes or entire chip
Can be reprogrammed without removing from device
8. Monitoring and Control Systems
8.1 Sensors and Actuators
Sensors are input devices that measure physical properties (temperature, pressure, light, etc.). They produce analogue data which must be converted to digital using an ADC (Analogue to Digital Converter).
Actuators are output devices that accept signals from the computer and turn them into physical movement. Also called output transducers (convert one form of energy to another).
Example: Central Heating System
Thermostat monitors room temperature → If below preset, boiler switched on → Temperature rises → When target reached, heating turns off → Process repeats automatically (feedback loop).
9. Buffers
A buffer is a temporary storage area created for data transmitted from one part of a system to another. It functions as a queue.
📖 Purpose of Buffers
Solves problem when data can be sent faster than it can be received
Data enters buffer before being transmitted to destination
Functions as a queue - data emerges in order it entered
Typically created in computer memory
Example: Printer buffer stores data while printer processes it
10. Key Takeaways
📌 Summary Points
Primary Memory
RAM: Volatile, read-write, stores current programs/data
Actuators: Output devices creating physical movement
Feedback: Essential for control systems to self-adjust
11. Exam-Style Questions
1. A computer has hardware and software. The hardware includes different types of memory. Complete the description: RAM and ROM are both examples of ______ memory. One item stored in RAM is ______. One item stored in ROM is ______. SRAM uses transistors arranged as ______. DRAM uses transistors and ______. [5 marks]
Answer:
RAM and ROM are both examples of primary memory
One item stored in RAM is currently running software/data/part of the OS
One item stored in ROM is the start-up/boot-up instructions/BIOS
SRAM uses transistors arranged as flip-flops
DRAM uses transistors and capacitors
2. Describe the principal operations of a magnetic hard disk drive. [5 marks]
Answer:
The hard disk has one or more platters/disks
Each surface of the platter is capable of being magnetised
The surface is divided into concentric tracks/circles
The disks are rotated at high speed
Each surface has a read/write head mounted on an arm positioned just above the surface
3. A car has several features including a lane detection system. This system monitors the lines on either side of the lane. If the car gets too close to one line, the system automatically moves the car away. Explain why the lane detection system is an example of an embedded system. [3 marks]
Answer:
The lane detection system is built into/integrated into the car
The system only performs one (specific) task
The system is not easily changed/updated by the car owner
4. Explain the differences between DRAM and SRAM. Include their use in devices and systems. [6 marks]
Answer:
DRAM uses transistors and capacitors, needs constant refreshing, slower access, cheaper, used as main memory
SRAM uses flip-flops, no refreshing needed, faster access, more expensive, used in processor cache
DRAM has higher capacity per chip than SRAM
SRAM is used where speed is more important than storage size (cache memory)
DRAM is used where larger amounts of cheaper storage are required (main RAM)
SRAM consumes less power under normal use; DRAM uses more power due to refreshing
5. Describe how data is stored on a solid state (flash) memory device. [4 marks]
Answer:
Data is recorded in transistors called Floating Gates
Uses NAND or NOR based flash memory which retains data without power
Cells are protected by floating gates and connected in series
Control Gate controls charge flow from Source to Drain
NAND-based memory reads faster than it writes; access is by blocks, not individual bits
6. Describe the operation of a laser printer. [6 marks]
Answer:
Data sent to printer driver and stored in printer buffer
Drum given electric charge and revolves step by step
Laser beam directed across drum, either switched on (discharge) or off (leave charge)
Charged toner coats drum, sticking only to discharged positions
Drum rolls over charged paper, transferring toner
Paper passes through heated rollers to fuse toner onto surface
7. Describe the differences between PROM, EPROM, and EEPROM. [6 marks]
Answer:
PROM: Can be programmed once only; uses fuse matrix; cannot be erased
EPROM: Can be erased using UV light; must be removed from device; entire chip erased at once
EEPROM: Erased using electric voltage; can remain in circuit while being reprogrammed; specific bytes can be erased
PROM used in: mobile phones, RFID tags
EPROM used in: development applications, older arcade machines
EEPROM used in: BIOS chips, smart cards, USB flash drives, SSDs
8. A burglar alarm system uses sensors to detect intruders. Describe how this monitoring system works. [5 marks]
Sensor data passed through ADC to convert analogue to digital
Microprocessor samples data and compares with preset values
If data outside acceptable range, signal sent to sound alarm/flash lights
Alarm continues until system reset with password
9. Explain the difference between a monitoring system and a control system. Give an example of each. [4 marks]
Answer:
Monitoring system: Passively collects data; does not interact with or change environment; no actuators involved
Control system: Actively manages process; takes action based on data; uses actuators; output affects input (feedback)
Monitoring example: Weather station, patient monitoring in hospital, burglar alarm
Control example: Central heating system, automatic irrigation, traffic lights, anti-lock braking
10. Explain the importance of feedback in a control system. Use the example of a central heating system. [5 marks]
Answer:
Feedback ensures system operates within given criteria
Enables system output to affect subsequent system input
Allows conditions to be automatically adjusted
Central heating example: Thermostat monitors temperature → if below preset, boiler turns on → temperature rises → when target reached, heating turns off → cycle repeats
Without feedback, system could not self-correct or maintain desired conditions automatically
12. Exam Success Tips (Part 1)
💡 Memory Types - Key Reminders
RAM = Volatile (lost when power off), ROM = Non-volatile (retained)
DRAM = Dynamic = Needs Refreshing (think: dynamic people need constant attention)
SRAM = Static = Stable (holds data without refreshing, used in cache)
SRAM is faster but more expensive → used for cache memory
DRAM is cheaper with higher capacity → used for main memory
💡 ROM Types - Remember the Pattern
PROM = Programmable ONCE (like burning a bridge - can't go back)