Field Guide · hardware

Also known as: SSD

A solid-state drive (SSD) is a storage device that keeps data in non-volatile flash memory with no moving parts, delivering far faster access than a mechanical disk.1

ctrl SSD — NAND flash chips any block reached electronically · no moving parts HDD — spinning platter seek arm must swing to the track · slower random access
An SSD is a controller wired to NAND flash chips, so any block is reached electronically; a hard disk must physically swing a seek arm to the right track on a spinning platter, which is why the SSD wins decisively on random access.

Overview

Where a hard disk drive seeks a head across spinning platters, an SSD reads any block electronically, so random access is orders of magnitude quicker and there is no mechanical latency, noise, or vibration sensitivity. A controller manages the underlying NAND, spreading writes across cells (wear leveling) because each flash cell endures only a limited number of erase cycles, and remapping cells that wear out. Endurance is often quoted as TBW — total bytes that can be written over the drive’s life.

SSDs connect over the older SATA interface, which caps around 550 MB/s, or over NVMe on a PCI Express link for several times that throughput and much lower latency. Either way the medium is the same NAND flash; the interface just sets how fast the host can reach it.

SSD vs HDD

The two fill the same role but trade off very differently:

Trait SSD HDD
Moving parts None Platters + heads
Random access Very fast Slow (seek + rotate)
Sequential speed High Moderate
Cost per TB Higher Lower
Durability Shock-resistant Sensitive to shock
Wear limit Erase cycles (TBW) Mechanical wear

Where it fits

In the memory hierarchy an SSD sits between RAM and slow bulk disk: not as fast as memory, but vastly faster than an HDD for the random reads a file system and database generate. For GopherTrunk, an SSD is the natural home for the active database of decoded calls and recent recordings — its quick random writes keep up with a busy control channel — while cheaper HDD capacity holds the long-term archive.

Sources

  1. Solid-state drive — Wikipedia, on flash-based drives and how they differ from mechanical disks. ↩

See also