Computer Storage Devices: Types, Examples and How They Compare
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A computer storage device is any hardware that holds data, either temporarily while the computer is working or permanently so it's still there after you switch off. Storage is usually divided into primary storage (fast, working memory such as RAM) and secondary storage (permanent storage such as SSDs and hard drives), plus removable and cloud storage.
Types of storage at a glance
| Type | Examples | Keeps data without power? | Purpose |
|---|---|---|---|
| Primary (main memory) | RAM, CPU cache, ROM/firmware | RAM and cache: no. ROM: yes | Holds what the CPU is working on right now |
| Secondary (internal) | NVMe SSD, SATA SSD, hard disk drive (HDD) | Yes | Stores the operating system, apps and files |
| Removable / external | USB flash drive, external SSD/HDD, SD and microSD cards, optical discs | Yes | Moving files, backups, cameras and phones |
| Network and cloud | NAS boxes, Google Drive, OneDrive, iCloud | Yes | Sharing, syncing and off-site backup |
| Archive (tertiary) | Tape (LTO), cold cloud storage | Yes | Long-term archives, mostly in businesses |
Primary storage
RAM (random access memory)
RAM is the computer's short-term working space. Apps and files are loaded from the SSD into RAM because RAM is much faster. It's volatile: everything in it disappears when the power goes off. Typical amounts in 2026 are 8–16 GB for everyday laptops and 32 GB or more for gaming and creative work. Our guide to RAM vs storage explains the difference in detail.
Cache
Very small, very fast memory built into the processor that keeps the most-used data closest to the CPU cores.
ROM and firmware
Read-only (or rarely rewritten) memory on the motherboard that holds the BIOS/UEFI firmware, which starts the computer.
Secondary storage
Solid-state drive (SSD)
SSDs store data on flash memory chips with no moving parts, so they're fast, silent and shock-resistant. They come in two main kinds:
- NVMe SSD (M.2 slot, PCIe): the standard in modern PCs. PCIe 4.0 drives reach about 7 GB/s and PCIe 5.0 drives over 12 GB/s. See what a PCIe SSD is.
- SATA SSD (2.5-inch or M.2 SATA): limited by the SATA interface to about 550 MB/s, but still far faster than a hard drive. See SATA vs SSD.
Hard disk drive (HDD)
Hard drives store data magnetically on spinning platters read by a moving head. They're slower (about 100–280 MB/s) and more fragile than SSDs, but much cheaper per terabyte, and the largest models now hold well over 20 TB. They're mainly used for backups, NAS boxes and large media libraries. See what a SATA hard drive is.
Removable and external storage
- USB flash drives: small and cheap; good for moving files and creating Windows install media.
- External SSDs: pocket-sized and fast (1,000–2,000 MB/s over USB-C 3.2 or USB4).
- External HDDs: the cheapest way to get several terabytes for backups.
- SD and microSD cards: used in cameras, phones, drones, the Nintendo Switch and handheld PCs.
- Optical discs (CD, DVD, Blu-ray): mostly legacy now, but still used for archives, films and some software. See our guide to burning a CD in Windows.
Speed and cost compared
| Device | Typical speed | Typical sizes | Good for |
|---|---|---|---|
| RAM (DDR5) | Tens of GB/s | 8–64 GB | Running apps |
| NVMe SSD (PCIe 4.0/5.0) | 3,500–14,000 MB/s | 512 GB–4 TB | OS, apps, games |
| SATA SSD | ~550 MB/s | 256 GB–4 TB | Upgrading older PCs |
| HDD | 100–280 MB/s | 1–24 TB+ | Backups, bulk storage |
| External SSD | 1,000–2,000 MB/s | 500 GB–4 TB | Portable fast storage |
| USB flash drive | 30–400 MB/s | 32 GB–1 TB | Moving files |
| microSD card | ~100 MB/s (UHS-I) | 64 GB–1 TB | Phones, cameras, consoles |
How storage works together
When you open an app, the CPU asks for it, the SSD reads it, and it's copied into RAM. The CPU then works on it from RAM and cache. When you save a file, it's written back to the SSD so it survives a restart. That's why a fast SSD makes a PC start and open apps quickly, and why more RAM helps when you run many apps at once.
Storage units from smallest to largest
| Unit | Size | Roughly holds |
|---|---|---|
| Bit | 0 or 1 | The smallest unit |
| Byte (B) | 8 bits | One character of text |
| Kilobyte (KB) | 1,000 bytes | A short text file |
| Megabyte (MB) | 1,000 KB | A photo or an MP3 song |
| Gigabyte (GB) | 1,000 MB | A film in HD; an app |
| Terabyte (TB) | 1,000 GB | Hundreds of thousands of photos |
| Petabyte (PB) | 1,000 TB | Data-centre scale |
Why does my 1 TB drive show 931 GB? Drive makers count 1 TB as 1,000,000,000,000 bytes, while Windows counts in binary units (1 GB = 1,073,741,824 bytes). It's the same space measured two ways; nothing is missing.
How to check storage on your computer
- Windows 11: Settings → System → Storage shows used and free space by category. To see the drive type, open Task Manager → Performance → Disk (it shows SSD or HDD).
- Windows 10: Settings → System → Storage, or open File Explorer → This PC.
- Mac: Apple menu → System Settings → General → Storage.
- Android and iPhone: Settings → Storage (Android) or Settings → General → iPhone Storage.
Which storage should you buy?
- New PC or upgrade: an NVMe SSD of at least 1 TB for Windows and apps.
- Old PC that feels slow: replacing its hard drive with a SATA SSD is the best-value upgrade.
- Backups: an external HDD or SSD plus a cloud copy (the "3-2-1" rule: 3 copies, 2 types of media, 1 off-site). See how often to replace an external hard drive.
- Gaming: 1–2 TB NVMe; modern games often need 100 GB or more each. See is 500 GB enough for gaming.
FAQ
What are the 4 types of storage devices?
Commonly: primary (RAM), magnetic (hard drives), solid-state/flash (SSDs, USB drives, memory cards) and optical (CDs, DVDs, Blu-ray). Cloud storage is often added as a fifth.
Is RAM a storage device?
It's primary memory. It stores data only while the computer is on, so it isn't used to keep files.
Which storage device is fastest?
Among permanent storage, NVMe SSDs on PCIe 5.0 are fastest. RAM and CPU cache are faster still but temporary.
What is the most common storage device today?
The NVMe SSD inside laptops and desktops, with cloud storage alongside it.