HDD (Hard Disk Drive)

Before there were computers, people had to go about carrying files and documents containing all the information they needed. Entertainment warranted cassettes and CDs while photographs went into albums. With the commercialization of the personal computer—and the invention of the HDD or Hard Disk Drive—it has become a cakewalk to store data. The HDD is the primary non-volatile hardware device of your computer that stores pivotal data including the operating system and critical software. Since it is “non-volatile,” the data is retained even after you switch off the computer.

HDD (Hard Disk Drive)

With time, HDDs have become more efficient at data storage and retrieval. Let us understand all about them in this go-to guide.

Origin of HDDs

HDDs have been around for decades; the first ones were launched by IBM in 1956[i]. Back then, the HDD only had about 5MB of storage space, cost $50,000, and couldn’t be removed from the computer. Eventually, in 1980, IBM came up with a hard drive that offered 1GB of storage and cost $40,000.

Technology has evolved considerably since then, with brands like Seagate following up on IBM’s efforts and launching their HDDs. Sizes have exploded from a few MBs of data to 12TB HDDs that can, virtually, accommodate your entire world. The cost of storage per gigabyte has also come down monumentally. Brands like Seagate now offer competitive costs of $0.04 per gigabyte of data[ii].

How Does an HDD Look?

Typically, HDDs come in two sizes—2.5” and 3.5”. They evolved from large discs (up to 20” in diameter)[iii] to their modern size. Simply put, an HDD is a boxed assortment of a platter mounted on a spindle, featuring a read/write head and arm.

HDD components
source: https://www.researchgate.net/figure/Mechanical-components-of-a-typical-hard-disk-drive_fig8_224323123

The platter(s) is the “disk” that spins when a hard drive is working. Multiple platters translate into more storage space. On the back of the drive is a circuit board (“disk controller”) that enables the HDD to communicate with the computer.

How Does an HDD Work?

An HDD stores data on its platter(s) which, in turn, is divided into sectors and tracks. When you format a hard drive, the tracks and sectors get formed. A track is a concentric circle; a sector is a wedge on a track. Every sector has a fixed number of bytes.

Inside the hard drive is a map of the sectors that have already been used up and those that are free to store new data. If you use the Windows operating system, this map will be called the File Allocation Table or FAT[iv]. The computer consults this map to figure out where and how to store data. Here’s what happens inside the drive to read/write data:

  • When you want to read/write data, the hard drive comes into operation. The platter spins (usually at speeds of 5400 to 15,000 rotations per minute).
  • The computer consults the sector-map (FAT) to see which sectors are free.
  • Accordingly, it instructs the read-write head to move to the corresponding location. During the rotation, the read/write arm reads/writes data across the platter, as required.
  • The data is stored at the farthest available track, and the read/write heads move inwards from there. All the data is stored magnetically, which is why it is non-volatile and retained after the computer is powered off.

Types of HDDs

At present, there are three types of HDDs[v] based on the kind of connector they use:

  • Small Computer System Interface (SCSI): These drives were the first to be launched to cater to the need of an interface between the computer and its peripherals. Early SCSIs used a 50-pin flat ribbon connector and allowed 7–15 devices to be connected at the same time. Modern-day SCSIs offer speeds up to 80 megabytes/second. They are, however, very expensive. For instance, a Seagate Ultra320 SCSI hard drive of 146GB costs around $116.99[vi].
  • Parallel Advanced Technology Attachment (PATA): These drives use 40-wire cables (or 80-wire cables) to connect to the CPU board. They are also known as Integrated Drive Electronics (IDE) or Enhanced Integrated Drive Electronics (EIDE) drives. Using PATA, you can connect up to two devices per channel. Their speeds are up to 133MiB/s[vii]. Their cost-effectiveness over the SCSI is remarkable, and PATAs continue to be used in industrial setups.
  • Serial ATA (SATA): Onwards to the most popular connector of the present times—the SATA. These drives use a different, much smaller connector than the PATA drives. Typically, a SATA cable has nine pins and is compact enough to fit into personal computers. They are also more efficient and consume less power. Their speeds are much greater than those of PATA drives—between 150MiB/s and 600MiB/s. You can connect only one device per connector.

Note that HDDs can also be classified based on whether they are external or internal. Another way to sort them is based on their grade: desktop-class or enterprise-class. The latter are high performers and can support up to 100% data usage.

Purchasing an HDD: Factors to Consider

While searching the market for an HDD, there are multiple factors to consider. Let’s evaluate them.

  • Size/Capacity: If you need to get an HDD that can store a lot of offline data including photos, videos and music files, you should consider high-capacity drives upwards of 2TB. But if you prefer online/cloud storage, you’ll be able to get by with smaller HDDs up to 1TB (or lower).
  • Device/Purpose: The HDD you purchase will also depend on the use you’ve set out for it—to go with a laptop, desktop, tablet or phone. You can also explore gaming-special HDDs if that’s what floats your boat. The Seagate Barracuda (3TB) is among the best gaming HDDs available in the market today[viii]. You can purchase it from Amazon.
  • Speed: Do you need super-fast data retrieval? A 7200 RPM will be a better pick than a 5400 RPM HDD. Remember that the rotations per minute are not an absolute measure of performance; you also need to consider the density of bits storage on the platters (areal density). Higher areal densities result in improved performance. Between two HDDs of the same areal density, the RPM is a good metric—a 7200 RPM HDD will perform about 33% better than an HDD with a 5400 RPM speed[ix].
  • External or Internal: Consider if you want to upgrade the internal HDD of your computing device or get an external HDD for data backup purposes. External drives are incredibly handy for data transfer, portability, and backup.

Leading HDD Manufacturers

The top HDD manufacturers of these times include Seagate, Toshiba, Hitachi, Western Digital, and HGST. While HDDs will typically come with the purchase of a new computer, you can buy an HDD via e-tailers like Amazon. Prices will vary depending on the capacity of the drive, whether it is internal or external, and the speed. For instance, a 1TB SATA HDD by Western Digital running at 7200 RPM is available for as little as $45.99[x]. A 6TB gaming hard drive by Toshiba, on the other hand, will set you back by around $164.99[xi].

Reasons for HDD Failure

If you use your computer frequently, it is not unusual to witness a gradually ailing HDD that’s slower and noisier than it used to be. The main reasons HDDs tend to fail after prolonged use include[xii]:

  • The HDD could be damaged because of overheating. This usually happens due to inadequate ventilation or malfunctioning computer fans.
  • You use your computer on a highly fluctuating power supply. Sudden power surges can bring on the failure of your HDD.
  • The HDD could be corrupt or suffer from a manufacturing defect.
  • Your computer could have been attacked by a virus that damaged the HDD or erased your data.
  • You could have installed the HDD or the operating system incorrectly. Making modifications in system registry settings can also impact the performance and life of an HDD.

Tips to Make Your HDD Last Longer: Care & Troubleshooting

Here are some quick ways to ensure you make the most of your hard drive:

  • Carry your computer carefully, avoiding knocks and falls. Avoid removing the HDD from its case unless you have to transfer it to another device.
  • Ensure your laptop is free of dust. If dust accumulates near the drive, it can affect the functioning as well as the airflow circulation.
  • Remember that excessive heat can destroy an HDD. Keep your computer’s fans functional and up to date. You can purchase a separate laptop cooler if you deem it necessary.
  • Defragment your drive periodically. (You can easily do it using inbuilt tools that come with your OS.) This optimizes the read/write functionality and prolongs disk life. Warning: Don’t defragment too often. The standard recommendation is to do it when the drive reaches 5–10% fragmentation[xiii].
  • If your hard drive is not being recognized by the computer, you can proceed with software recovery using tools like TestDisk[xiv]. It is best to seek expert advice unless you are trained to repair/replace drives.

Tip: Always backup your data. Avoid using an HDD to store critical information that’s not backed up elsewhere. This is because no matter how cautiously you use your computer, the passage of time increases the probability of failure of an HDD. You can choose between local backup and online backup. For the former, you can use network-attached storage (NAS) devices. You can purchase single-drive NAS devices for less than $200[xv]. For online backup, you can choose services such as IDrive or Acronis[xvi]. This option is more reliable as service providers store several copies of your data across different servers. The servers are also protected in “hardened data centers,” thereby ensuring that your data is fully insulated from damage or loss.

Related Posts

Signs Your HDD is about to Fail

It is time for you to change or upgrade your hard drive if you notice the following signs:

  • Your waiting times to read/write data have increased exponentially.
  • The computer crashes frequently.
  • You get strange error messages or distorted output when you attempt any data-related tasks like copying or pasting files.
  • Your data (say, certain files) seems to be disappearing.

Also, it is a good idea to monitor the heat and noise levels of the drive. If you notice your drive creaking/grinding more frequently than before, it could signal a mechanical failure that you should get checked to avoid data loss.

HDD in the Modern Times: Evolution & Comparison with SSD

Even though HDDs have been around for a long time, their popularity is being increasingly threatened by SSDs—solid state drives that use flash memory instead of moving parts to store data. SSDs offer efficient, high-speed and quiet storage and this is making them the storage device of choice in contemporary computers. Capacity-wise too, the world might soon see a 100TB SSD—the Nimbus Data ExaDrive DC100—which is more space than you could possibly use[xvii].

  HDD vs. SSD
Cost HDDs are more cost effective per gigabyte of data. SSDs are considerably more expensive.
Speed HDDs are slower at reading/writing data. Boot-up time is also higher for HDDs.
Heat & Noise HDDs generate noise while working, unlike SSDs which are quiet. Ditto for heat produced.
Capacity HDDs offer more space—up to 12TB. Large-capacity SSDs still have low commercial viability.
Power Consumption HDDs consume more power and hence, use up more battery life.

The table makes it clear that HDDs are much cheaper and typically offer more storage space. SSDs tend to be expensive but are incredibly fast and power-efficient. When choosing between an HDD and an SSD, you should be guided by your needs and budget.

Closing Note

In the decades since 1956 when IBM launched the first hard drive, things haven’t stopped evolving. Modern-day HDDs are compact and store terabytes of data at a minimal cost (as low as three cents per gigabyte[xviii]). As of 2017, some of the most expansive HDDs included HGST’s 12TB Ultrastar and Seagate’s 12TB Enterprise Capacity drive[xix]. However, to continue being the primary choice for data storage, HDDs will have to keep evolving and endeavor to match the dazzle and speeds of SSDs.


[i] https://www.computerhope.com/jargon/h/harddriv.htm

[ii] https://www.cloudwards.net/history-of-the-hard-drive/

[iii] https://computer.howstuffworks.com/hard-disk1.htm

[iv] https://www.explainthatstuff.com/harddrive.html

[v] https://techspirited.com/hard-drive-types

[vi] https://www.amazon.com/Seagate-Cheetah-10K-7-Ultra320-ST3146707LC/dp/B003490AQ8

[vii] https://hexus.net/tech/tech-explained/storage/18827-pata-vs-sata/

[viii] https://www.wepc.com/reviews/best-gaming-hard-drives/

[ix] https://www.seagate.com/in/en/tech-insights/choosing-high-performance-storage-is-not-about-rpm-anymore-master-ti/

[x] https://www.amazon.com/Blue-Cache-Desktop-Drive-WD10EZEX/dp/B0088PUEPK/

[xi] https://www.amazon.com/Seagate-Portable-External-Photography-STDR2000100/dp/B00FRHTSK4/

[xii] https://www.stellarinfo.com/blog/6-worst-reasons-of-hard-disk-failure/

[xiii] https://www.makeuseof.com/tag/care-hard-drives-make-last-longer/

[xiv] https://www.cgsecurity.org/wiki/TestDisk

[xv] https://www.wd.com/en-um/solutions/what-is-network-attached-storage-nas.html

[xvi] https://www.pcmag.com/article2/0,2817,2288745,00.asp

[xvii] https://www.zdnet.com/article/worlds-largest-ssd-hits-100tb/

[xviii] https://www.backblaze.com/blog/hdd-versus-ssd-whats-the-diff/

[xix] https://hddmag.com/top-x-largest-hard-drives/