What Is A Computer Hard Drive?

One thing that has stayed a rock solid constant in a computer over all these decades of their evolution has been the hard drive. Other components have changed dramatically as technology has surged forward, and while that may be true for the hard drive as well, their over all look and style hasn’t differed much over the years. This is because a hard drive doesn’t need to change its appearance in order to do its job. It’s what’s on the inside that counts after all!

So, what is a computer hard drive? A hard drive (often called hard disk drive, or shortened to HDD, or HD) is a non-volatile memory storage device that uses hard disk platters for permanent data storage and retrieval using a magnetic head. A hard drive is an air tight casing that rests in a drive bay and is connected to the motherboard via an ATA, SCSI, SATA, or IDE cable. A hard drive is connected to the power supply unit (or PSU), where it draws its power to function.

Every computer requires a hard drive of some kind to function, as there’s no alternative to hold all the data needed to sync up your components. Without the hard drive your operating system, personal files, and all your programs would have no where to be stored.

It’s important to note that a hard drive is not to be confused with RAM (Random Access Memory). RAM is a temporary storage component that allows for faster access to recently used files and data. When you power off the computer, all RAM data is wiped clean. Hard Drives retain their memory permanently unless deleted by the user.


Understanding Hard Drive Terms

Hard Drives are complicated computer components with a lot of parts to them. They’ve also continued to evolve over the years with new technology being added. Despite this, some older technology still continues to stick around and so newer users might find themselves a little overwhelmed at all the different terms used when discussing hard drives. I’ll provide a list below of some of the more important things you need to know about hard drives and their parts!

Hard Disk Drive – Commonly called a HDD. An air sealed case consisting of a number of hard disk platters that have information magnetically recorded onto them via a read/write head.

Solid State Drive – Commonly called a SSD. SSDs contain no moving parts like an HDD and do not store information magnetically and as a result can store and retrieve data much quicker than an HDD.

Disk Platter – Typically an aluminum or ceramic disk that holds the magnetically written data inside an HDD. When the computer is powered, these disks spin at high rotations per minute (RPM). Different HDD models have different RPM speeds and generally the higher the better.

Expansion Bay – Otherwise simply known as a bay or drive bay, an expansion bay is where additional drive are installed into a computer case. Examples include CD-ROM and DVD-ROM drives as well as Hard Drives. They come in 3.5-inch and 5.25-inch sizes.

ATA – Short for Advanced Technology Attachment. This is an older connection interface for add on drives like CD-ROM and hard drives. This has since been replaced with SATA which most secondary drives use today.

SATA – Short for serial AT attachment (or sometimes called SerialATA). SATA is used by most modern hard drives and much faster than ATA. It also has the benefit of being backwards compatible with ATA.

SCSI – Short for Small Computer System Interface. This was a connection interface that was widely used in Apple and Unix computers in the 1980s and 1990s. Like ATA, it has been almost universally replaced by SATA.

IDE – Short for Integrated Development Environment. This was a connection interface commonly used for hard drives along with ATA. Like most others, it has long since been replaced by SATA.

Read/Write Head – Often referred to as RW Head. This is part of the actuator arm inside the hard disk drive and is used to both read and write data onto the hard disk platters. Most HDDs typically have an RW head for each disk platter inside.

Access Arm – Or more commonly called a head arm or actuator arm. This arm is in every hard disk drive and looks similar to a record player. As the disk platters spin, the actuator arm adjusts the RW heads in order to store or retrieve data.

Spindle – A spindle is the part of the HDD that holds the disk platters in a fixed position while leaving enough room between each disk for the actuator arms to fit between them.

Megabyte – Commonly referred to as MB. This is a measurement of data that determines how much information a hard drive can hold. Older hard drives may only hold a few hundred megabytes.

Gigabyte – Commonly referred to as GB. This is a measurement of data that determines how much information a hard drive can hold. A single gigabyte is composed of a thousand megabytes.

Terabyte – Commonly referred to as TB. This is a measurement of data that determines how much information a hard drive can hold. A single terabyte is composed of a thousand gigabytes.

Not all of these terms will be something you’ll often hear, but it’s always a good idea to have an idea of what they mean. Especially if you intend to be working with or replacing a hard drive inside your computer.

A Closer Look at a Hard Drive

HDDs are still the most common hard drive in computers today. What does it actually do though? Why this brick of a component so important to the operation of the rest of the computer? Well, without a hard drive, the rest of the computer would have no place to draw the data it needs to properly function.

The important thing to remember is that a hard drive stores everything about your PC in one convenient spot. Not only does it store all the data on your operating system, it also stores data on the specifications of all your other components. This data is what allows your operating system to sync with the components of your computer. Your hard drive is essentially the library that your motherboard and operating system use to understand and communicate with everything else in your computer!

If you’re intending to replace or buy a hard drive, there are some things you’ll want to keep in mind.

  • HDDs are commonly found in 2.5-inch and 3.5-inch sizes. Laptops use 2.5 while desktop computers use 3.5
  • SSDs are faster than HDDs but more expensive. These are normally used to store your most crucial files
  • The speed of an HDD is determined by the RPM (rotations per minute) that it operates at. The faster the RPM, the faster the HDD can read and write data
  • You should always buy new. Used HDDs and SSDs have too much risk involved with them. You don’t want to buy a used hard drive and have it fail on you shortly after your purchase
  • Don’t undersell yourself. Buying a faster hard drive with more storage space is always the way to go as long as you can afford it

These are just some simply things to consider when you’re purchasing a new hard drive. It can be a pain to replace all the lost files if your hard drive failed, but the process of buying a new one should at least be a very simplistic and quick process!


How Does a Hard Disk Drive Work?

As mentioned before, an HDD has a lot of moving parts to it. Motors are whirling, actuator arms are moving, and disk platters are spinning. All at many thousands of RPM. It can be pretty complicated!

Thankfully, most users will never have to physically open a hard drive case, but it’s still important to know how all those parts are working when your computer is powered on.

Once your computer is powered on, the disk platters will begin spinning and the motors powering the actuator arms will come to life. These actuator arms will travel across the disk platters whenever a request for data is sent to the HDD.

The disk platters work on a spindle and are always in motion. This allows the RW head at the tip of the actuator arms to more quickly reach the data. This works very similarly to a record player, but the information is read from the inside of the disk to the outside, rather than from the outside edge to the inside like a record.

All this data is read and written magnetically on an HDD using binary. Meaning that all computer information stored on a hard drive is written in a long combination of 1s and 0s.


Other Types of Hard Drives

There are a few types of storage devices other than the typical HDD. Some you may have already heard of and some were even mentioned in this article!

The most common hard drives are typically HDD, SSD, Laptop HDD or SSD, Flash Drive, and External Hard Drive.

Unlike HDDs and SSD, flash drives and external drives are not installed inside your computer case and are instead connected and powered via a USB plug. The amount of data these devices can hold vary quite wildly and can be very affordable ways to store small bits of important information that you can more easily transport around.

It’s important to keep in mind that flash drives are quite small and can be lost easily. So make sure that you’re not putting them in places you can easily forget about.

External hard drives are very convenient for mass storage of data, however they’re extremely vulnerable to accidents. Dropping them on hard surfaces or spilling liquid on them can quickly ruin the external hard drive. Extra care must be taken when using one of these! If you’d like to read more about portable hard drives, I wrote an article about them here.


Putting it All to Memory (Conclusion)

Hard drives are an amazingly complex and robust component of your computer. They’re critical pieces of technology that carry a lot of the heavy lifting of a system. In the future, we’ll likely see HDDs phase out use, but that won’t happen for quite some time.

Now that you know more about what a computer hard drive is, don’t hesitate to leave any comments or questions below and I’ll make sure to get back to you directly!


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