Hard disk drive
Hard Disk Drive (HDD)
A Hard Disk Drive (HDD) is an electromechanical device used for storing digital data. It stores and retrieves information using magnetic storage on one or more rapidly spinning disks, called platters. Data is written to and read from these platters by magnetic heads, which move across the disk surfaces on an arm. HDDs are a form of permanent storage, meaning they keep your data even when the power is off.
For many years, HDDs were the main type of storage in computers for operating systems, applications, and user files.
What HDDs are For
HDDs provide lasting storage for digital information. Unlike temporary computer memory (RAM), HDDs hold onto data indefinitely until you remove it or the drive breaks. They offer large storage capacities at a relatively low cost per gigabyte, making them ideal for holding vast amounts of data.
The speed of an HDD is affected by how fast the platters spin and how long it takes for the read/write heads to find the correct spot on the disk.
Main Parts of an HDD
An HDD has several key physical parts inside a sealed case:
Platters: These are rigid, circular disks with a magnetic coating where data is stored. Several platters are often stacked together.
Spindle Motor: This motor spins the platters at a constant high speed (e.g., 7,200 revolutions per minute).
Read/Write Heads: Tiny electromagnets on the end of an arm that read and write data. They float just above the platter surface.
Actuator Arm: A movable arm that holds the read/write heads and moves them across the platters to access different data areas.
Logic Board (PCB): The electronic circuit board that controls the drive's operations, managing data transfer and head movements.
How an HDD Works
When your computer needs to access data on the HDD:
The spindle motor spins the platters to full speed.
The actuator arm moves the read/write heads to the correct position over the data track.
As the specific data spot spins under the head, the head either:
Reads: Detects magnetic changes and converts them into digital data.
Writes: Changes the magnetic polarization on the platter surface to store digital data.
The time it takes for the heads to move and for the correct data to spin into place are the main factors limiting HDD performance, especially for quickly accessing scattered pieces of data.
HDD vs. SSD Comparison
| Feature | HDD | SSD |
|---|---|---|
| Moving Parts | Yes (spinning platters, moving arm) | No (all electronic) |
| Speed (Access) | Slower (milliseconds) | Much Faster (microseconds) |
| Speed (Overall) | Slower (up to ~250 MB/s for common types) | Much Faster (hundreds to thousands of MB/s) |
| Durability | Lower (sensitive to shock/vibration) | Higher (more resistant) |
| Power Use | Higher | Lower |
| Noise | Can be audible | Silent |
| Cost per GB | Lower | Higher |
| Capacity | Typically higher max capacities | Max capacities increasing, but often trail HDDs |
Typical Uses
Even with the rise of SSDs, HDDs are still widely used for specific tasks:
Bulk Data Storage: Storing very large amounts of data where cost is a main concern, such as large media libraries or archives.
Backups: Storing copies of data due to their high capacity and lower cost.
Archiving: Long-term storage of data that isn't accessed often.
Server Storage: Used in servers, especially for tasks involving large data writes or requiring huge storage capacity where extreme speed isn't needed for all data.
HDDs in Pulsed Media Services
Pulsed Media uses enterprise-grade SAS HDDs across its seedbox and server infrastructure. These drives differ from consumer SATA drives in several ways:
- Designed for 24/7 operation in multi-drive server environments
- SAS interface provides higher bandwidth and supports dual-port connections for redundancy
- Vibration tolerance — enterprise drives include rotational vibration sensors, important when dozens of drives share a chassis
- Higher MTBF (Mean Time Between Failures) ratings compared to consumer drives
Storage is organized in RAID arrays: RAID0 in V-series plans (maximum throughput for seeding), RAID5 in M-series plans (redundancy with parity). Capacities range from hundreds of GB on shared seedbox plans to tens of terabytes on dedicated servers.