Few things can breathe new life into a computer the way a hard drive upgrade can. One of the most important parts of a computer, the internal hard drive stores the operating system, applications, and all your data, including documents, photos, music, and videos.

In recent years, hard drives have taken massive leaps forward in terms of storage space and performance. At the same time, while a hard drive upgrade used to be an expensive proposition – prohibitively so for the largest storage options – replacing the internal hard drive is now one of the least expensive ways to improve your computer.

If you’re unsure where to start your search, we can help. Our buying guide highlights some internal hard drives that we think stand out from the crowd, and it also includes plenty of information to point you in the right direction as you shop.

When shopping for an internal hard drive, there are several things you need to consider, including storage type, capacity, speed, and other features.

Internal hard drives are divided into three distinct categories: the traditional magnetic storage hard disk drive (HDD), the solid-state drive (SSD) and the hybrid drive.

HDD: The HDD is the oldest type of internal hard drive, invented in 1954. HDDs store data using spinning platters coated with a magnetic material, while a magnetic head mounted on a moving actuator arm reads data from the platter and writes data to it. Rather than storing data sequentially, HDDs store data using random-access methods. This means that with proper mapping of the data stored on a platter, the hard drive can access any individual blocks of data equally fast, regardless of where the blocks are encoded on the platter.

Because this technology is so mature and the components are relatively cheap, HDDs offer the best combination of storage and price. The downside is that HDDs are susceptible to damage. Because the magnetic head is hovering above the platter with a clearance as small as three nanometers, a significant shock can cause the head to make contact with the platter, resulting in severe damage. Modern drives have built-in shock nullification features, but even with the best countermeasures, this kind of damage is always a risk. In addition, because the HDD stores data magnetically, exposure to a strong magnet can erase or corrupt it.

SSD: This is a completely different approach to hard drive design, using solid-state memory (similar to that used in smartphones or tablets) in lieu of spinning platters. Because there are no moving parts, SSDs provide much faster read/write speeds than HDDs. Their biggest disadvantages are price and storage capacity. The widespread use of solid-state memory in phones and tablets keeps the demand and corresponding costs higher than those of HDDs.

Since they have no moving parts, SSDs overcome the inherent fragility of the traditional HDD design. In addition, they’re immune to magnetic corruption. Because SSDs store data in electrical charges, they have an endurance rating, essentially a lifespan for optimal safe use. Endurance has to do with how much data can be written to the drive over a certain period, such as five years. Drives that are past their endurance rating are susceptible to data loss if left without power.

Hybrid drive: The third option combines the benefits of both types of hard drive. Hybrid drives use traditional magnetic platters to provide large storage capacities combined with smaller, faster SSD storage for frequent or high-intensity operation.

One of the biggest factors most people look for when comparing hard drives is capacity. Measured in gigabytes (GB) – one gigabyte equals 1,024 megabytes – or terabytes (TB) – one terabyte equals 1,024 GB – most HDDs currently on the market offer hundreds of gigabytes on the low end and multiple terabytes on the high end. Commonly available SSDs range from 128 GB to 2 TB.

Speed is another important factor to consider when shopping for an internal hard drive, especially when looking at HDDs. Because the magnetic platters are spinning, the drive’s read/write speed is directly related to how fast the platters spin.

“Green” drives are the slowest of the spinning hard drives, at 5,400 rpm, with lower power consumption being their main selling point. This makes them a good choice for mobile computers, especially in settings where battery consumption must be optimized.

Standard hard drives usually spin at 7,200 rpm and offer a good balance of performance and energy use.

High-performance drives spin at 10,000 rpm and are best suited for desktop computers.

Another factor to consider is the size of the internal hard drive bay. Most desktop computers have bays designed to take a 3.5-inch hard drive, while most laptops use the smaller 2.5-inch profile.

Internal hard drive cache plays a similar role as a computer’s random-access memory (RAM). A computer uses RAM to hold the operating system and whatever programs or data you’re working on, which speeds things up since RAM provides much faster data access than a hard drive. A hard drive’s cache holds data in memory while the hard drive reads and writes to the platter. The larger the cache, the faster a hard drive can process data.

Just like a computer, internal hard drives have processors that control the drive’s functions. While many hard drives have single-core processors, high-performance drives have multi-core processors that can handle data faster and improve the overall performance of the drive.

Inexpensive: Internal hard drives have dropped in price over the years to the point that even the largest are reasonably priced. Entry-level hard drives under 1 TB, that spin at 5,400 rpm, and have 8 MB of cache cost less than $50.

Mid-range: These drives have higher performance, with capacity as high as 2 TB and 64 MB or 128 MB of cache, and they spin at 7,200 rpm. These drives cost $50 to $200.

Expensive: High-end drives are 6 TB or larger, spin at 7,200 or 10,000 rpm, have 256 MB of cache, as well as multi-core processors. Expect to pay over $200.

• Repurpose an internal drive you’re not using. You can buy an enclosure that effectively turns it into an backup external hard drive.
• Select a hard drive that’s compatible with your computer. Hard drives connect to the motherboard via different types of interface, the most common being SATA or IDE.
• Look for an internal hard drive with built-in shock protection. This is especially important if you’re purchasing a hard drive for your laptop, and especially if you use it on the go.
• Buy the fastest internal hard drive you can afford. Hard drives are the weak link in a computer’s performance. Try to buy the fastest-performing hard drive you can to help alleviate that bottleneck.
• Opt for one or two platters. While it’s impossible to avoid moving parts in HDDs, try to buy one that has one or two platters. While consumer drives can have as many as five individual platters, the more platters a drive has, the more heat it generates and the greater the potential for failure.

In addition to the products we’ve reviewed above, there are a couple more we’d like to mention. The Western Digital WD Black Performance Hard Drive has 6 TB of storage, 7,200 rpm, 256 MB of RAM, dual-core processors, and a five-year warranty. The drive is aimed at heavy users, such as gamers, creatives, and other professionals, and is priced accordingly. The Toshiba MK3276GSX Internal Hard Drive is a 320 GB drive running at 5,400 rpm. This inexpensive drive is a good choice for low-power uses.

Q. I bought a drive that had been sitting on a shelf for a while. Does that eat into my warranty?
A. No. The warranty begins on the date of purchase.

Q. What type of warranty can I expect?
A. Most drives come with a three-year warranty, but some come with a five-year warranty.

Q. Do hard drives come with any software?
A. Some do. Depending on the manufacturer, some internal hard drives come with software that helps you clone and migrate the data from your existing hard drive.