Hard Disk Drives utilize mechanical, spinning magnetic platters and dynamic read/write heads to store data. They are primarily classified by their use case, interface types, and physical sizes.
┌────────────────────────────────────────────────────────┐
│ HDD Internals │
│ ┌─────────────────┐ │
│ │ O Platters │ ◄── Magnetic Storage Media │
│ │ ╱ │ │
│ │ ── Actuator Arm │ ◄── Mechanical Head Assembly │
│ └─────────────────┘ │
└────────────────────────────────────────────────────────┘
Physical Dimensions & Form Factors
- 3.5-Inch Desktop Drive: Measures 101.6 mm × 146 mm × 26.1 mm. Used universally in desktop computers, network-attached storage (NAS) towers, and servers.
- 2.5-Inch Laptop/Mobile Drive: Measures 69.85 mm × 100 mm. Thickness varies between 7 mm, 9.5 mm, or 15 mm for high-capacity external configurations.
- 1.8-Inch Ultra-Mobile Drive: Legacy standard measuring 54 mm × 78.5 mm × 5 mm / 8 mm. Found in early iPods and vintage ultra-thin laptops.
Data Interfaces & Revisions
- PATA / IDE (Parallel ATA): Legacy ribbon cable connection using a 40-pin or 44-pin layout. Max bandwidth is 133 MB/s (ATA/133).
- SATA (Serial ATA): Uses a distinct L-shaped 7-pin data connector and a 15-pin power connector.
- SATA I (1.5 Gb/s): Max 150 MB/s throughput.
- SATA II (3.0 Gb/s): Max 300 MB/s throughput.
- SATA III (6.0 Gb/s): Max 600 MB/s throughput.
- SCSI (Small Computer System Interface): Early enterprise system utilizing 50-pin, 68-pin, or 80-pin parallel ribbons. Max speeds topped out around 320 MB/s (Ultra-320 SCSI).
- SAS (Serial Attached SCSI): The modern enterprise evolution of SCSI, using a point-to-point serial architecture compatible with SATA physical footprints.
- SAS-1: 3.0 Gb/s per lane.
- SAS-2: 6.0 Gb/s per lane.
- SAS-3: 12.0 Gb/s per lane.
- SAS-4: 22.5 Gb/s per lane.