Field Guide · hardware

Also known as: storage, data storage

Storage is where a computer keeps data long-term, so that files and programs survive a power cycle.1 It is the permanent counterpart to RAM.

RAM · working memory SSD · flash — no moving parts HDD · spinning platters magnetic tape · archive volatile ↑ non-volatile ↓ faster · smaller larger · cheaper · slower the CPU works in RAM; anything worth keeping sinks to the tiers below
Every storage device is a point on one speed-versus-cost curve: RAM at the top is fast but volatile, and each step down — SSD, hard disk, tape — is larger and cheaper per byte but slower. The dashed line is the volatile/non-volatile split: only RAM loses its contents at power-off, which is why the CPU works in memory and writes anything lasting to the tiers below.

Overview

Storage comes in a few common forms:

  • HDD (hard disk drive): data on spinning magnetic platters — cheap and high-capacity, but slower and mechanically fragile.
  • SSD (solid-state drive): flash memory with no moving parts — faster, quieter, and more rugged.
  • Flash memory: the non-volatile technology inside SSDs, SD cards, and the on-board storage of small devices.

All of these are non-volatile — they hold their contents with the power off, unlike RAM. The trade-off is speed: even fast storage is much slower than RAM, which is why the CPU does its active work in memory and reads from or writes to storage only when it must.

Where it fits

Storage is one of the four building blocks of computer hardware. On a single-board computer it is often a microSD card; on a microcontroller it may be a small block of on-chip flash; on a server it can be racks of SSDs.

Sources

  1. Computer data storage — Wikipedia, on non-volatile storage and HDD/SSD/flash technologies. ↩

See also

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