If RAM is like your computer’s short-term memory then you can think of the hard drive as the long-term memory. It’s where you store your files and programmes when you’re not using them, and they’ll stay there when you turn your computer off. 

How big your hard drive needs to be will depend entirely on what you plan to use your computer for. If all you’re planning on is doing a little web browsing and word processing on Windows 10 then you might get away with a 120 gigabyte (GB) drive - but you may find that it fills up pretty quickly, especially if you’re using your computer to save photos or videos, or do any gaming. 500 GB will give you much more headroom. And if you’re a heavier user - playing modern games, or doing content creation - then you’ll want a minimum of 1 terabyte (TB), and even more is better. 

The good news is that storage space is pretty cheap - so upgrading shouldn’t be too much of a struggle.

There are several different types of hard drives, available in a huge range of different capacities. If you have a desktop PC then there’s a good chance you’ll be able to install more than one, and of different types too. If you have a laptop or all-in-one (AIO) PC, you might be more limited. 

As with a lot of computer terminology, the name hard drive is a throwback to earlier days. A hard drive is a kind of mass storage device. Early computers used linear storage, like magnetic tape or even audio cassette tapes, for mass storage. These were replaced with non-linear disk (short for diskette) storage - large capacity, permanently installed hard disks and low capacity, removable floppy disks. Both consisted of magnetic platters which could be spun at high speed, and accessed by a tiny, fast-moving read/write head. A hard drive has the read/write head as part of a sealed unit with the platter, floppy disks slot into a drive which contains the read/write apparatus. 

The technology used in magnetic-platter-based hard disks (originally invented in 1956) is still available in today’s hard disk drives (HDDs). It’s got a lot smaller and a lot faster, but the basic principle of a magnetic disk and a read/write head remains the same. 

Recently though, a new technology has become commonplace - solid state drives (SSDs). These use solid-state technology - a bit like what makes up the RAM in your computer, or on the memory card in your camera. 

SSDs are much faster than traditional HDDs. So much so in fact that they have become faster than the interface between the drive and the motherboard used by HDDs, known as a serial advanced technology (SATA) connection. 

As SSD tech has improved, a new interface called M.2 has been introduced. This allows small, high-capacity, high-speed, low-power consumption drives to plug directly into the motherboard and utilise either SATA or PCIe NVMe connection buses for varying degrees of speed. 

So what does that mean, and which is right for you? Let’s take a closer look. 

As we talked about in our RAM article, a terabyte is 1,024 gigabytes. A gigabyte is made up of 1,024 megabytes, which is made up of 1,024 kilobytes and so on. But what does that actually mean to you? 

Well, the easiest way to understand that is to look at how much storage capacity different things need. 

So the first thing you’ll have taking up space on your hard drive is your operating system (OS) - probably Windows 10 or 11, MacOS or some version of Linux.

Microsoft says that the minimum requirement for available storage space for Windows 11 is 64 GB. But that’s not the whole story. If you have a clean install of Windows 11 (that means it’s not an upgrade of an old version of Windows 10) then it’s likely to take up around 27 GB on your machine when everything is finished. An upgrade from Windows 10 could take substantially more. 

Still, that’s much less than the 64 GB Microsoft suggests, right? So a smaller hard drive should be plenty. 

Maybe not. 

First, you need to remember that Windows (or whatever OS you’re using) needs room to move files around on your hard drive. And if your storage gets too full, you’ll notice that things slow right down and you keep getting pop-up messages warning you of low space. 

With that in mind, you probably want to keep at least 5-10 GB free at all times. Add that to your Windows installation and you’re up to around 35 GB already. 

But things don’t stop there. Microsoft releases regular updates for Windows, and it’s important to install these to keep your computer up-to-date and secure. So you’ll need to make sure you keep at least around 10 GB free for updates on top of what Windows already needs. So now we’re up to about 45 GB, and we haven’t even installed anything other than Windows yet. 

Now it’s possible that you’ll be able to do everything you want to with your PC just with the built-in apps that come with Windows, but chances are that you’ll want to install some more to be able to do what you want. Let’s have a look at how much space some common apps take. 

If you want to use a different web browser, then Chrome needs around 400 MB (a bit less than half a gigabyte) and Firefox uses almost 700 MB. 

Microsoft Office 365 will take up 3-4 GB depending on which components you need, though it’s worth bearing in mind that many Office apps can be accessed online or replaced with web-based alternatives like Google Docs.  

Creativity apps can take up a huge amount of space - Adobe recommend that you have a minimum of 20 GB free before you even install Photoshop, 

And if you want to play games then things can fill up very, very quickly. Modern games designed to run at high resolutions at incredible detail need a vast amount of space. Ark: Survival Evolved with all of its expansions and maps requires a mammoth 400 GB of hard drive space - but even something relatively lightweight like Fortnite needs 26 GB. 

Even drivers for your graphics card can run into hundreds of megabytes. 

Chances are you won’t just want to install apps and games - you’ll want to save your own files too. So let’s have a look at how much space they might take up. 

The good news is that saving text-only Word documents doesn’t take much space at all - a few kilobytes (KB) each. But as soon as you start adding in pictures, that size can balloon to several megabytes very quickly. 

Speaking of pictures, a 16-megapixel jpg taken on your phone could be around 6 MB in size. That doesn’t sound much, but multiply it by several hundred and you’re soon up to gigabytes of storage just for photos. And if you use a modern camera like a DSLR or mirrorless system, and shoot in raw or high-quality TIFF, you’ll find image files can easily be 60-70 MB. 

If you like to shoot video then filesizes can get really big. It will depend on your device, but one minute of full HD footage shot on a phone will be around 130 MB, while 4K footage takes that up to a massive 350 MB per minute. That means a ten-minute video clip could be 3.5 GB. 

So if you want to store your photos and videos on your computer, you’ll need plenty of space. 

If you want to store media - like movies and music - on your PC then you’ll need lots of space for that too. A top-quality 4K movie can be anything from 15 GB to 30GB, while a standard HD movie will be between 4 and 6 GB. 

A decent-quality MP3 song will be around 10 MB, which means you’re looking at around 100 MB for an album, or 1 GB for ten. Songs saved in a lossless compression format like FLAC will be more like 30 MB per song or 300 MB for an album. If you have a big music collection, you’ll need a lot of space to store it. 

Of course, if you use streaming services like Disney+ and Netflix for your movies and Spotify for your music then storage won’t be at such a premium. But bear in mind that streaming services will still need a decent chunk of storage space to cache what you’re watching or listening to. 

Add all those bits together and it’s easy to see how you could soon find your hard drive filling up. 

As we mentioned earlier, there are three distinct types of hard drives on the market today - and all of them have their own pros and cons, depending on how you plan to use them and what you expect. 

Let’s have a look at the different types and find out a little more about them. 

Mechanical HDDs are the oldest tech on the market by far - but that means that they’ve had a long time to be refined into the pinnacle of that technology, and it also means that you can get a lot of storage space for not very much money. 

HDDs are generally available in two sizes - 3.5” for desktop PCs and 2.5” for laptops (although there are plenty of adapters to let you fit a 2.5” drive in a desktop case if you want). Inside is a magnetised platter that can spin at speeds of up to 7,200 RPM depending on the drive, and a read/write head on an arm that can scan back and forth across the surface of the platter incredibly quickly. 

Any drive you buy for your home PC will use a cabled serial advanced technology attachment (SATA) interface. Others are available but tend to be used in servers or older legacy PCs. 

The main advantage of HDDs is the amount of storage space available at a very low cost. You can have 4 TB of storage for under £100, and 6 TB for not much more. 

There are a couple of disadvantages to mechanical HDDs. First and foremost is that they’re slow. The max read/write speed for an HDD is around 150 MB/s. They’re also quite power-hungry due to the spinning platter (although nowhere near as much as your GPU will be) and susceptible to damage from impact and incorrect shutdown if the read/write head is not properly parked. 

SSDs have been gaining in popularity since the early 2000s and most new PCs now come with one for storage. They use similar (but not identical) technology to RAM and USB sticks, but they’re much cheaper than RAM and much better suited to constant rewriting than USB storage. 

Like HDDs, SSDs use a SATA connection to the motherboard and come in a 2.5” case. But instead of a load of moving parts inside, all you’ll find is a series of memory chips. 

SSDs currently offer a great balance between performance, capacity and cost. They’re more expensive than mechanical HDDs - you’ll be looking at a 2 GB drive if you want to keep the cost under £100 - but they’re much faster. A decent SSD using the most recent SATA 3 connection to your motherboard will transfer data at a maximum rate of around 550 MB/s. That’s much faster than an HDD, and you’ll really notice the difference when booting up Windows or opening apps and files. 

A SATA SSD will also use less power than a mechanical HDD due to the complete lack of moving parts. It will also be less likely to be corrupted by an incorrect shutdown or impact (though we wouldn’t recommend testing this). In the early days, flash memory technology in SSD drives had a shorter lifespan than mechanical HDDs. But the technology has improved since then, and for the home user longevity is no longer really a concern.

As SSD technology improved, it wasn’t long before it outpaced the ageing SATA connection standard, which was initially developed for slower mechanical HDDs and optical drives like CD and DVD ROMs. This led to the introduction of the M.2 form factor and the nonvolatile memory express (NVMe) interface, which runs on the peripheral component interconnect express (PCIe) bus. 

That sounds complicated, but don’t worry - there are only a few things you really need to know. 

M.2 refers to the size and shape of the drives, which is reflected in the naming. They can be between 16 and 30 mm wide, though almost all are 22 mm. The length varies more, especially in laptop drives and devices like the Steam Deck, with sizes between 16 and 110 mm available. You’ll see this when a drive has something like M.2 2280 in the title - referring to a width of 22 mm and a length of 80 mm, which is fairly common. A longer length doesn’t necessarily mean more capacity, but it can allow more physical space for memory modules. 

To confuse matters a little, drives in the M.2 format can use either a SATA or an NVMe PCIe interface. A SATA M.2 drive will be limited to speeds of around 550 MB/s as with SATA SSDs. So what you really want is an NVMe M.2 drive, which can have transfer speeds of up to 5,000 MB/s depending on the drive. Even budget devices will have speeds of as much as 3,500 MB/s, which is a huge increase from a SATA SSD. 

The biggest benefit of M.2 NVMe drives is their speed. They’re also much smaller than any other option, which makes them great for slimline laptops, and they only sip tiny amounts of power. 

So what are the disadvantages? 

Well, the biggest one was the cost. But recently the price gap between SATA and M.2 NVMe drives has closed considerably, and you can currently pick up 2TB for under £100. You’ll also need to be sure that your motherboard has the right connection, which it might well not if it’s an older model.

You could - but it’s not recommended. 

USB drives are brilliant for the applications they’re designed for - like transferring files between computers or storing photos on your camera. What they’re not great at - because they’re not designed for it - is the constant high-speed writing and rewriting that hard drives are subjected to. 

Even if you buy a good quality one from a reputable retailer the controller and memory chips won’t be designed for use as a hard drive, plus you’ll be limited to the speed of the USB interface which is much slower than an NVMe drive. You’ll also be paying more per GB of storage than you would with a dedicated hard drive.

If you don’t buy a good quality one from a reputable retailer then you’re taking a big gamble with your data. Certain online selling sites are saturated with what appear to be big-name USB sticks with enormous capacities for next to no money. Not only are these almost certainly fake, made with much lower quality parts than genuine ones, they usually lie about their capacity too. 

Sure, the ad might say you’re getting a 2 TB drive for a few quid. Windows might even believe it when you pop it in too. But actually, you’re getting a much smaller capacity drive (usually 8 GB - 32 GB) with some minor modifications made to the way it works so it looks like a much bigger drive. When you try to write more than the real capacity of the drive to it, Windows will think that it’s working - but as soon as you remove it, your files will disappear. 

Cheap USB drives are not worth the risk regardless of your planned use. If it seems too good to be true - it probably is. 

Well, as ever, that depends on what you want to use your PC for. 

First up, whatever you plan on using your computer for, it’s worth having either a SATA or NVMe drive for your operating system and most used applications. It will give you a huge speed boost over a mechanical HDD and make your computer much nicer to use. If you’re on a tight budget and you need more storage space than you can afford in an SSD then you could then extend your space with a secondary mechanical HDD. If you have a desktop you can add a second internal drive; in a laptop or AIO PC, you’re probably limited to a single internal drive. But you can always use an external USB HDD or SSD for extra space. 

Which takes us back to the question of exactly how much space you need. 

If you’re planning on very basic usage - a bit of web browsing, some emails and word processing - then you might get away with a small 120 GB drive. But there’s a good chance that you’ll find yourself running out of space after not too long, especially if you want to try out some of the other amazing things that you can do with a PC. If you can afford it, it’s really worth trading up to at least 240 GB, or 500 GB if you can stretch. 

If you want to get stuck into some content creation, with photo or video editing, then you’re going to need much more space. You should consider 1 TB the minimum to get started, with 2 TB or more being a better option. You might also want to consider a bigger HDD as a backup drive to archive your old projects, where the decrease in speed won’t be such a disadvantage. 

If you’re a gamer and you want to play modern games then at least 1 TB of fast SSD should be the minimum you’re aiming for, and even then you might find yourself having to juggle game installs when you run out of space. 2 TB or even more would be great if your finances can stretch. You don’t really want to have a second slower drive as any games you install on there will always feel slow and compromised. 

The nice thing about storage is that it’s rarely difficult to add more. If you have a desktop, then there should be room for a few drives in there, so it can grow with you. If you have a laptop or AIO PC, plugging in an external hard drive can be a great solution if you need more space. 

It’s worth over-speccing your main drive as much as you can, in terms of both speed and space. You’ll really notice a difference in how responsive your computer is, and how quickly it completes tasks.