What is spindle speed?
Spindle speed is how fast a hard disk drive's platters rotate, measured in revolutions per minute (RPM). The platters sit on a motor-driven spindle and spin the whole time the drive is active. The read/write heads can only reach a sector when it passes under them, so the faster the platters spin, the sooner the data arrives.
Common spindle speeds
| RPM | Average rotational latency | Where you'll see it |
|---|---|---|
| 5,400 | About 5.6 ms | Laptops, external USB drives, low-power drives |
| 7,200 | About 4.2 ms | Desktops, many NAS and high-capacity drives |
| 10,000 | 3 ms | Enterprise server drives, often SAS |
| 15,000 | 2 ms | High-performance enterprise SAS drives |
Average rotational latency is the time for half a revolution, the average wait for a sector to come around: 60 seconds divided by the RPM, then divided by 2.
What higher RPM changes
- Faster access: lower rotational latency means quicker random reads and writes, and usually higher sequential transfer rates too.
- More heat, noise and power: the motor works harder, which matters in laptops and quiet PCs.
- More vibration: fast drives benefit from solid mounting, especially in multi-drive enclosures.
- Cost and capacity: 10,000 and 15,000 RPM drives cost more per gigabyte and come in smaller capacities.
Spindle speed vs. SSDs
SSDs store data in flash memory chips and have no platters, spindle or heads, so they have no RPM and no rotational latency. Even a 15,000 RPM drive is far slower at random access than a typical SSD. Spindle speed only matters when you're comparing hard drives, for example picking a 7,200 RPM drive over a 5,400 RPM drive for a desktop's data disk.
Because a hard drive is mechanical, grinding or clicking noises can mean the motor or heads are failing. Back up the data right away.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.4 names spindle speeds alongside the 2.5-inch and 3.5-inch hard drive form factors. Know the common values (5,400, 7,200, 10,000 and 15,000 RPM), that higher RPM means faster access but more heat and noise, and that SSDs have no spindle. Objective 5.2 lists grinding noises and clicking sounds as drive symptoms.