Storage devices are used to permanently store data such as the operating system, software, documents, and media files. The two main types of internal storage in modern computers are HDD (Hard Disk Drive) and SSD (Solid State Drive).
Storage devices connect to the motherboard through SATA or NVMe (PCIe) interfaces. The storage architecture influences performance, boot speed, file access time, and system responsiveness.
| Type | Storage Medium | Data Access | Moving Parts | Speed | Cost |
|---|---|---|---|---|---|
| HDD | Magnetic disk | Mechanical | Yes | Slower | Cheaper per GB |
| SSD | Flash memory | Electronic | No | Faster | Expensive per GB |
| Parameter | Description |
|---|---|
| Type | HDD (magnetic), SSD (NAND flash), Hybrid (SSHD) |
| Interface | SATA III, NVMe (PCIe Gen 3/4/5), mSATA, U.2 |
| Capacity | Ranges from 120GB to multiple TBs |
| Form Factor | 3.5” (HDDs), 2.5” (SSD/HDD), M.2 (SSD), U.2 (Enterprise SSDs) |
| Read/Write Speed | HDD: 80–160 MB/s, SATA SSD: 500–600 MB/s, NVMe SSD: 2000–7000+ MB/s |
| Cache (Buffer) | Small RAM built-in for quick access to recent data (e.g., 64MB, 256MB) |
| MTBF (Reliability) | Mean Time Between Failures – SSDs usually offer higher reliability |
Common Interfaces: SATA II, SATA III
Form Factors: 3.5” (desktop), 2.5” (laptop)
Types of SSDs:
| SSD Type | Interface | Form Factor | Notes |
|---|---|---|---|
| SATA SSD | SATA III | 2.5” | Slower, compatible with most systems |
| NVMe SSD | PCIe (x4) | M.2 | Very fast, requires M.2 slot |
| M.2 SATA SSD | SATA | M.2 | Same performance as 2.5” SATA SSD |
| U.2 SSD | PCIe | U.2 | High-end enterprise use |
| Component | HDD Description | SSD Description |
|---|---|---|
| Storage Medium | Magnetic platters that store binary data using magnetized sectors | NAND flash memory cells that store data electronically |
| Controller | Manages data read/write operations, caching, and interface handling | Manages data access, wear leveling, TRIM, error correction, and over-provisioning |
| Cache (Buffer Memory) | Small DRAM cache (e.g., 64MB, 256MB) to temporarily store frequently accessed data | Typically DRAM or HMB (Host Memory Buffer) used for fast data access |
| Read/Write Head | Mechanical arm that moves across platters to read/write data | Not applicable (SSD is solid-state, no moving parts) |
| Spindle Motor | Spins the platters at constant speed (e.g., 5400 RPM, 7200 RPM) | Not applicable |
| Platters | Circular magnetic disks inside the HDD that store data in tracks and sectors | Not applicable |
| Actuator Arm | Moves the read/write head to the correct position on the platters | Not applicable |
| PCB (Circuit Board) | Controls all functions, connects to power and data interface | Controls NAND flash, interfaces, and power management |
| Interface Connector | SATA or SAS interface for data transfer to motherboard | SATA or PCIe (NVMe) interface for high-speed data transfer |
| Firmware | Controls internal logic of the drive, including error handling and calibration | Controls flash translation layer (FTL), garbage collection, wear leveling |
| Bus Interface | Used For | Speed Approx. |
|---|---|---|
| SATA III | HDDs, 2.5” SSDs | ~600 MB/s |
| PCIe Gen 3 | NVMe SSDs | ~3.5 GB/s |
| PCIe Gen 4 | High-end NVMe SSDs | ~7 GB/s |
| USB 3.2 | External drives | ~1 GB/s |
| Task | Recommended Storage |
|---|---|
| OS Boot Drive | SSD (preferably NVMe) |
| Games & Apps | SSD |
| Backups & Media Files | HDD |
| Video Editing (Cache) | High-speed NVMe SSD |
| Budget PC Builds | Hybrid (120GB SSD + 1TB HDD) |
💡 For a fast and responsive PC, an SSD is essential. HDDs still hold value for inexpensive, large-capacity storage needs.