Performance Metrics: When evaluating hardware, engineers use the CASPR framework: Capacity (how much data), Access Speed (latency and throughput), Storage Cost (price per GB), Portability (size/weight), and Reliability (durability and lifespan).
Environment Matching: Selection must account for the physical context. For example, high-vibration environments (like a moving vehicle) require Flash storage over Magnetic storage because Magnetic drives are susceptible to head crashes from physical shock.
Accessibility Requirements: Specialized I/O devices are selected based on user ability. Braille displays provide output for visually impaired users, while eye-tracking cameras serve as input for users with limited motor control.
| Feature | Magnetic (HDD) | Optical (CD/DVD) | Flash (SSD) |
|---|---|---|---|
| Mechanism | Moving mechanical parts | Laser reflection | Electronic circuits |
| Speed | Moderate latency | High latency (slow) | Very low latency |
| Capacity | Very High (Terabytes) | Low (Megabytes/Gigabytes) | High (Terabytes) |
| Durability | Fragile (shock sensitive) | Fragile (scratches) | Robust (no moving parts) |
| Cost | Lowest per GB | Low per unit | Highest per GB |
Scenario Analysis: Exams often ask for a device recommendation for a specific persona (e.g., a professional photographer). Always justify your choice using at least two factors, such as 'SSD for high-speed file transfers' and 'Portability for field work'.
Input vs. Output Identification: Be careful with multi-functional devices. A touchscreen is both an input device (sensing touch) and an output device (displaying images). In an exam, specify which function you are referring to.
Capacity Units: Ensure you understand the scale of data. A typical document might be measured in Kilobytes (), while a high-definition movie requires Gigabytes (). Choosing a storage medium with insufficient capacity is a common error.
Storage vs. Memory: A frequent mistake is using 'memory' to refer to the hard drive. Memory (RAM) is volatile and used for active processing, while Storage (HDD/SSD) is non-volatile and used for long-term retention.
The 'Infinite' Flash Life: While Flash storage is durable against drops, it has a finite number of write cycles. Every time data is written, the physical cells degrade slightly, meaning SSDs eventually wear out if used for constant high-volume logging.
Speed vs. Bandwidth: Students often confuse the time it takes to start reading a file (latency) with the amount of data transferred per second (bandwidth). Optical drives have poor latency because the physical laser must move and the disc must spin up.
