Drives are a crucial component of modern computers that allow for long-term data storage and retrieval. There are several common types of drives used in computers today.
Hard Disk Drives (HDD)
Hard disk drives (HDDs) have been the traditional primary drive in computers for decades. HDDs use magnetic storage to store and retrieve digital data. Data is written and read via mechanical arms with read/write heads that move over the disk platters. HDDs have high capacity, are non-volatile (data is retained when powered off), and are inexpensive per gigabyte compared to solid state drives.
There are two main form factors of HDDs used in computers:
- 3.5 inch – Used in desktop computers. Higher capacity drives, typically up to 10TB currently.
- 2.5 inch – Used in laptops. Lower capacity, typically 500GB to 2TB currently.
HDDs have moving parts and can be damaged by shock or vibration. They also have higher latency for data access compared to solid state drives. However, HDD costs per gigabyte remain significantly lower than solid state drives.
Solid State Drives (SSD)
Solid state drives (SSDs) are increasingly becoming the primary drive in newer laptop and desktop computers. SSDs use flash memory with no moving parts to store data. This allows for much faster read and write speeds, better reliability due to lack of moving parts, and resistance to physical shock/vibration. However, SSDs remain more expensive per gigabyte than HDDs.
There are two main form factors of SSDs used in computers:
- 2.5 inch – Used in laptops and desktops. Capacity ranges from 120GB to 4TB currently.
- M.2 – Smaller SSD designed to plug directly into a computer’s motherboard. Used in laptops and desktops. Capacity ranges from 120GB to 2TB currently.
SSDs provide substantial performance improvements over HDDs which has led to their increasing adoption. Their lack of moving parts also makes them better suited for mobile computing applications where physical shock is a concern. However, the higher cost per gigabyte still limits SSD capacities in consumer systems compared to HDDs.
Hybrid Drives
Hybrid drives, sometimes called SSHDs (solid state hybrid drives), combine an HDD with a smaller SSD acting as cache for frequently accessed data. This aims to approach SSD speeds for more common tasks while retaining the HDD’s high capacity storage at a lower price point. The SSD caching algorithms are designed to detect patterns and store frequently used data on the faster SSD portions of the drive.
Hybrid drives are primarily found in laptops. They offer a compromise between HDD capacity and SSD speed. However, they still do not match the performance of pure SSDs and remain less common than traditional HDD or SSD laptop drives.
Optical Drives
Optical drives are able to read/write data from/to optical discs. The common types of optical drives found in computers include:
- CD drive – Reads/writes Compact Discs (CDs)
- DVD drive – Reads/writes Digital Versatile Discs (DVDs)
- Blu-ray drive – Reads/writes Blu-ray discs
Optical drives have fallen out of favor as cloud storage, large inexpensive HDDs/SSDs, and fast internet connections have reduced the need for physical optical media. However, they remain useful for accessing legacy media and in some cases writing very large files that exceed typical USB flash drive capacities.
Floppy Disk Drives
Floppy disk drives were the earliest non-permanent storage available for home computers. They read/write data to floppy magnetic disks. While floppy drives have been obsolete for over a decade, they were an important bridging technology from early home computers lacking hard drives until HDDs became inexpensive enough for home use.
Two main standards of floppy drives existed:
- 5.25 inch – Used in early home computers like the Apple II
- 3.5 inch – Smaller design used in 1980s/90s home computers before being displaced by optical drives
Tape Drives
Tape drives use magnetic tape reels to sequentially store large amounts of data for archival and backup purposes. They can offer high capacities with relatively low media costs but very slow data access. LTO (Linear Tape Open) is a common tape drive standard used for backups.
The key advantage of tape is its long term storage capacity, longevity, and cheaper media costs relative to HDDs/SSDs. However, the slow sequential access means tape is solely used for backup and archival with HDDs/SSDs used as the primary storage medium.
Flash Drives
Flash drives, also known as USB drives or thumb drives, use flash memory to store data. They connect to computers via USB ports. Key advantages include:
- Small physical size and weight
- No external power source required
- Re-writable storage
- Resistance to physical shock
While capacities remain below HDDs/SSDs, flash drive capacities have grown from megabytes to gigabytes with largest current models up to 2TB. Their portability has made them ubiquitous for transferring files between systems and portable data storage.
SD Cards
SD cards are flash memory data storage devices used in portable devices such as digital cameras, phones, handheld gaming consoles, and tablets. There are three sizes of SD cards:
- Standard – 24mm x 32mm x 2.1mm
- Micro – 15mm x 11mm x 1mm
- Mini – 21.5mm x 20mm x 1.4mm
SD cards use flash memory and have no moving parts, giving them fast access times and resistance to shock/vibration like SSDs. Capacities range from 4GB up to 1TB for standard SD cards currently. The small physical size and ubiquitous use in portable devices make SD cards a flexible portable storage medium.
RAID
RAID (Redundant Array of Independent Disks) allows multiple drives to be used together as a single logical drive to provide increased storage, speed, data protection, or a combination thereof. Some key advantages of RAID include:
- Increased storage capacity – Combining multiple drives adds space
- Improved speed – Spreading data across drives improves performance
- Redundancy/Data protection – Parity or mirroring protects against drive failure
There are several RAID standard levels with different methods of implementing the array:
- RAID 0 – Striping for performance
- RAID 1 – Mirroring for redundancy
- RAID 5 – Distributed parity for redundancy + capacity
- RAID 6 – Double distributed parity for added protection
- RAID 10 – Striping + mirroring
The flexibility of RAID allows balancing performance, capacity, and redundancy as needed by combining standard off-the-shelf drives into logical volumes.
Network Attached Storage (NAS)
Network attached storage (NAS) devices contain one or more internal drives and connect directly to a network to provide shared storage accessible by other devices on the network. This allows central storage and backups for servers, desktop clients, media streaming, and more. Key advantages of NAS include:
- Shared storage accessible from anywhere on the network
- User access controls and security
- Redundant capabilities through RAID
- Simplified data backups
NAS devices may use traditional HDDs, SSDs, or both combined. Capacities scale from terabytes to petabytes for enterprise-level NAS. Ease of use and network accessibility make NAS a convenient shared storage solution.
External Drives
External drives connect to a computer externally rather than internally. They are physical drives encased in an enclosure with standard interfaces/cables. Common types of external drives include:
- External HDDs
- External SSDs
- External optical drives
External HDD and SSDs typically connect via USB, Thunderbolt, Firewire, or eSATA interfaces. Key advantages include portability, easily moving data between systems, and expandable storage. External HDDs in particular offer large inexpensive storage options compared to flash drives.
Conclusion
Drives are crucial components in computers that provide non-volatile storage space for software, user files, and the operating system itself. The many drive types available offer a range of capabilities from ultra-fast SSDs to high capacity HDDs to huge networked storage. Determining the right drive involves balancing key factors like capacity, speed, portability and reliability for the intended use case.
