A hard drive is a key component of computers and many other electronic devices. It provides long-term storage for digital information, like documents, photos, music and applications. Here are some quick facts about computer hard drives:
– Hard drives store data magnetically on quickly rotating disks called platters. Data is read from and written to the platters using a moving arm with read/write heads.
– The space on a hard drive is measured in gigabytes (GB) and terabytes (TB). 1 TB is equal to about 1,000 GB. Standard desktop hard drives today often have capacities between 250 GB and 2 TB.
– Data on a hard drive is organized into files that are stored in folders or directories. The operating system keeps track of where files are located on the drive.
– Drives are connected to the computer through cable interfaces like SATA and SSD uses NAND flash memory to store data.
– Common types of hard drives in computers today include traditional HDDs (hard disk drives) and faster, more durable SSDs (solid-state drives). External portable hard drives can also be connected to computers.
How a Hard Drive Works
A hard drive consists of one or more rigid platters coated in a magnetically sensitive film consisting of tiny magnetic grains. The platters are mounted on a spindle which rotates at very high speeds, typically 5,400 RPM to 7,200 RPM for consumer hard drives.
Read/Write Heads
Above and below each platter is an actuator arm with a read/write head that can detect and alter the magnetic properties of the platter surface. As the disk spins, the head floats just above the surface on an air cushion, allowing it to move rapidly across the platter while barely touching it.
Information is recorded by orienting the magnetic particles so that they represent binary 1s and 0s. The presence or absence of a magnetic pulse in a specific location represents a data bit. As millions of these tiny magnetic regions pass by the head each second, they are decoded into data.
Tracks and Sectors
The platters are formatted into concentric circles called tracks, which are further divided into tiny wedges called sectors. This organization allows the drive heads to precisely target small regions on the disk when reading or writing data. The computer references data by the platter, track and sector numbers where it is located.
| Component | Description |
|---|---|
| Platters | Disks that store data magnetically |
| Read/write heads | Moves across platters reading and writing data |
| Spindle | Spins platters at high speed |
| Actuator arm | Moves heads across platters |
Data Storage
To store a file on a hard drive, the operating system divides it into chunks that will fit within a sector, which is typically 512 bytes in size. It then decides where to store each chunk – scattering the file fragments across available sectors across the platters and tracks. The locations of all the pieces of the file are stored in a file table maintained by the file system.
When a file is opened or edited and needs to be saved again, the fragments are rewritten to empty sectors wherever they happen to be available. This scattering and rewriting of file pieces is why previously deleted files can sometimes be partially recovered from an HDD.
Solid-state drives work a bit differently than HDDs, but they also store data in logical blocks that are assigned logical block addresses. External portable hard drives function the same way as internal ones.
File Systems
The file system organizes the sectors on the drive into files and folders. Common file systems for Windows include:
– NTFS – New Technology File System, the most modern Windows file system
– FAT32 – Fat32, an older file system still used for external drives
– exFAT – Extended FAT, used for high-capacity external storage
The file system maintains the file table and keeps track of which sectors belong to which file, and where each file’s name and details are stored. It checks the file table to determine where data should be read from or written when a file is accessed.
Hard Drive Interfaces
Hard drives use cable interfaces to connect to the computer system and transfer data between internal components. Here are some common hard drive interface types:
SATA
Serial ATA is the primary connection interface for modern internal hard drives. SATA data cables support transfer speeds up to 6 gigabits per second or 600 megabytes per second. SATA cables connect one drive to the computer’s motherboard.
SAS
Serial Attached SCSI (SAS) is a high-speed alternative to SATA used in enterprise servers and RAID setups. SAS supports multiple connected drives and hot swapping.
USB
External portable hard drives typically connect to PCs using a USB cable. Common USB versions like 3.2 gen 1 can support data transfer speeds around 5-10 gigabits per second.
eSATA
External SATA is designed for connecting external drives using fast SATA speeds. eSATA can support roughly the same speeds as internal SATA connections.
Thunderbolt
Thunderbolt ports can provide very fast 40 Gbps connections for high-performance storage devices including external hard drives. However, Thunderbolt hard drives remain relatively rare.
Hard Disk Drive vs. Solid State Drive
While HDDs have moving parts that make them fragile, SSDs are more durable since they have no moving parts. SSDs are therefore better suited for portable devices like laptops that may be moved while operating.
SSDs are also much faster than HDDs, with maximum sustained transfer speeds over 500 MB per second compared to HDD’s roughly 100 MB per second. However, HDDs have vastly higher storage capacities available. For most desktop PCs, pairing a smaller SSD to hold the operating system and applications with a high-capacity HDD is a good combination.
Here’s a comparison of HDDs vs SSDs:
| Hard Disk Drive (HDD) | Solid State Drive (SSD) | |
|---|---|---|
| Storage medium | Magnetic platters | NAND flash memory chips |
| Max. sustained transfer speed | ~100-200 MB/s | Over 500 MB/s |
| Capacity | Typically 500 GB – 6 TB | Typically 250 GB – 2 TB |
| File access time | Around 10-15 ms | 0.1 ms or less |
| Durability | Prone to damage from shocks when active | No moving parts, can withstand more shocks |
| Price (per GB) | Around $0.03 per GB | Around $0.20 per GB |
Common Hard Drive Capacities
Consumer hard drives are available in a wide range of capacities to support various storage needs. Some typical capacities for desktop and laptop hard drives include:
– 250 GB – Entry-level size for basic use
– 500 GB – Standard capacity for light use
– 1 TB – High capacity for moderate storage needs
– 2 TB – Very high capacity for extensive storage
– 4 TB – Maximum common single-drive capacity
Enterprise and specialty drives go even higher. For example, large RAID setups are available with 10 TB, 14 TB or even 20 TB drives for massive server storage needs.
Portable external hard drives have capacities in the same range as laptop drives. Small portable HDDs often have between 500 GB and 1 TB, while larger capacity portable drives go up to 5 TB.
Common Hard Drive Speeds
The rotational speed of a hard disk drive greatly impacts how fast it can read and write data. Some common HDD speeds include:
– 5,400 RPM – Common for entry-level desktop and laptop drives
– 7,200 RPM – Standard speed for mainstream desktop HDDs
– 10,000 RPM – Faster, higher performance drives, more common in servers
– 15,000 RPM – Top-end, high performance server drives
SSDs have much faster effective rotational speeds measured in the hundreds or thousands of RPMs, due to the lack of mechanical movement.
Transfer speeds also depend on the drive’s interface. SATA 3.0 drives can transfer data at up to 6 Gb/s, while USB 3.0 external drives may transfer data anywhere from 5 Gb/s for older ones up to 20 Gb/s for newer models.
Hard Drive Noise
Hard disk drives generate noise from the mechanical motion of the platters spinning and the movement of the actuator arms. Noises can include:
– Humming or whirring from the spindle motor
– Clicking sounds from the read/write heads moving
– Vibrations transmitted through the chassis
SSDs and flash drives have no moving parts so they operate silently. To reduce noise, some HDDs have QuietStep ramp features to dampen vibrations, as well as fluid dynamic bearing spindles for quieter motors. Noise-reducing casings and mounts can also help silence HDD noises.
Failure and Lifespan
Because of their mechanical nature, hard drives will eventually fail or wear out with age. However, modern drives can often last several years even with frequent daily use.
Some signs of a failing hard drive include:
– Bad sectors – Areas of inaccessible sectors develop
– S.M.A.R.T. errors – Reliability monitoring system reports issues
– Struggling sounds – Clicking noises indicating mechanical problems
– Failed reads/writes – Disk read/write failures
– Slow performance – Drive operates very slowly
To maximize lifespan, handle hard drives gently, keep them away from strong magnets, and try to avoid sources of shocks and vibrations.
Regular backups are essential to avoid data loss when a drive fails. Many external drives come with backup software to automatically copy important files for protection.
Data Recovery
When a hard drive fails, specialized data recovery techniques can often salvage some or most of the data. Here are some data recovery methods:
– Repair corrupted file system or partition tables
– Bypass failed read/write heads by accessing platters directly
– Replace failed drive components like circuit boards
– Use specialized recovery software to reconstruct data
– Transplant platters into identical working drive chassis
However, recovery can be expensive, difficult, or impossible depending on the drive damage. Again, backups are key to avoiding reliance on recovery.
Uses of Hard Drives
Some of the most common applications for hard drives include:
– Primary internal storage for laptop and desktop computers
– File servers in offices for central shared storage
– External portable backup drives for additional data protection
– Media servers for large music/video collections
– NAS (Network Attached Storage) appliances for home and office network storage
– DVRs for recording video surveillance footage
– Game consoles like the PlayStation and Xbox use specialized internal hard drives
– Car navigation and entertainment systems often use customized hard drives
Hard drives are also frequently used with external enclosures to expand the storage capabilities of various devices. For example, additional hard drives can provide more storage space for DVRs and video game consoles.
Conclusion
Hard disk drives continue to be a cost-effective, high-capacity data storage solution for consumers and businesses. Although SSDs are faster, HDDs store far more data per dollar spent. The future is likely to see HDDs retained for mass storage combined with smaller SSDs for speeding up access to frequently used programs and files.
Ongoing advances in hard drive technology include increasing areal densities for cramming more data onto platters, new kinds of magnetic recording like SMR and HAMR, and novel designs like Helium drives. However, hard drives remain fundamentally mechanical devices with physical limits to their speed and reliability. Solid state drives are likely to slowly displace HDDs in most roles as costs continue to decrease.