Hard Drive Capacity 解説
HDD vs SSD: 理解する Your Storage Options
Find Your StorageWhether you're buying a computer, upgrading storage, or adding an external drive, understanding hard drive capacity helps you make informed decisions. This guide explains how storage is measured, the differences between HDDs and SSDs, and how to choose the right capacity for your needs.
HDD vs SSD Comparison
| Factor | HDD | SSD |
|---|---|---|
| Technology | Spinning magnetic platters | Flash memory chips |
| Speed (sequential) | 80-160 MB/s | 500-7,000 MB/s |
| Speed (random) | ~1 MB/s | 50-400 MB/s |
| Capacity range | 500 GB - 20 TB | 128 GB - 8 TB |
| Price per GB (2024) | ~$0.02-0.03 | ~$0.08-0.15 |
| Durability | Sensitive to shock | More shock resistant |
| Noise | Audible spinning/clicking | Silent |
| Power consumption | 6-10 watts | 2-5 watts |
| Lifespan | 3-5 years typical | 5-10 years typical |
理解する Capacity Labels
Why Does My 1 TB Drive Show Less?
A drive labeled "1 TB" contains 1,000,000,000,000 bytes. But operating systems often display storage in binary units:
- 1 TB (manufacturer) = 1,000 GB
- Windows displays: 931 GiB (shows as "931 GB")
- Difference: ~7%
Formatted vs Raw Capacity
Additional space is used for:
- File system overhead (3-5%)
- Operating system (20-100+ GB)
- Recovery partition (500 MB - 10 GB)
How Much Storage Do You Need?
Light Use (256-512 GB)
- Operating system and programs
- Documents and spreadsheets
- Light photo collection
- A few large applications
Average Use (1 TB)
- All of the above, plus:
- Moderate photo library (10,000+ photos)
- Music collection
- Several games
- Some video files
Heavy Use (2-4 TB)
- Large game library (10+ modern games)
- Extensive photo/video collection
- Video editing projects
- Virtual machines
- Large software suites
Professional/Power User (4+ TB)
- 4K/8K video production
- Large databases
- Extensive game library (50+ games)
- Full system backups
- Media server content
Capacity Planning Guide
| Content Type | Typical Size | Files Per TB |
|---|---|---|
| Documents | 100 KB - 5 MB | 200,000+ |
| Photos (JPEG) | 3-10 MB | 100,000-300,000 |
| RAW photos | 25-60 MB | 17,000-40,000 |
| MP3 songs | 3-8 MB | 125,000-330,000 |
| HD movies | 4-8 GB | 125-250 |
| 4K movies | 20-50 GB | 20-50 |
| PC games | 30-150 GB | 7-33 |
SSD Types 解説
SATA SSD
- Speed: Up to ~550 MB/s
- Connection: SATA III (same as HDD)
- Price: Most affordable SSD option
- Best for: Upgrading older systems
NVMe SSD
- Speed: 2,000-7,000 MB/s
- Connection: M.2 slot (PCIe)
- Price: Moderate premium over SATA
- Best for: New builds, high performance
Form Factors
- 2.5-inch: Standard SATA SSD, fits HDD bays
- M.2: Compact stick form, SATA or NVMe
- PCIe card: Expansion slot mount, enterprise
External Drive Considerations
USB Standards Impact
| USB Version | Max Speed | 1 TB Transfer Time |
|---|---|---|
| USB 2.0 | 60 MB/s | ~4.5 hours |
| USB 3.0/3.1 Gen 1 | 625 MB/s | ~27 minutes |
| USB 3.1 Gen 2 | 1.25 GB/s | ~13 minutes |
| USB 3.2 Gen 2x2 | 2.5 GB/s | ~7 minutes |
| Thunderbolt 3/4 | 5 GB/s | ~3.5 minutes |
The drive's speed and USB port version both matter—you get the slower of the two.
まとめ
For most users in 2024, a 512 GB to 1 TB SSD provides excellent performance for the operating system and frequently used programs. Add a 2-4 TB HDD for media storage if needed. When buying, remember that advertised capacities use decimal measurement while your OS likely displays binary units—expect about 7% less usable space than the label suggests.