Hardware Laptops

What is an SSD? And how is it different from a hard disk?

what is an ssd
It's easy to be confused by SSD drives, so here goes nothing...

We do love our three-letter abbreviations in technology. In recent years, one particular trio of letters has come to the fore: SSD. So what is an SSD? How does it differ from a hard disk? And which type should you choose when buying a laptop?

Note this isn’t a deep-dive into SSD technologies. There are fabulous sites that go into great detail on this, such as StorageReview. It’s intended to give a helpful overview to aid the non-expert make a buying decision.

What is an SSD? SSD vs hard disk

SSD stands for solid state storage. The key word there is “solid”: nothing moves. That’s in stark contrast to a normal hard disk, which may look pretty solid on the outside, but contains a number of spinning metal plates within. It doesn’t take much imagination to see why this can get damaged, especially in computers that get carried about.

what is an ssd vs hard disk
The inside of a hard disk – the metal plate spins so that the reader (on the arm) can access the data

Reliability is just one of the advantages SSDs hold over hard disks. They’re lighter and much more compact, so you can squeeze them into those lovely thin laptops we all adore.

SSDs are much faster too. That means programs will open more quickly and data – such as the 10MB photo you took yesterday – should load near-instantly. What’s more, operating systems boot much more quickly.

However, just to complicate things, not all SSDs are born equal when it comes to speed. I cover that in a moment. Before we get bogged down in such things, though, a simple rule of thumb holds: SSDs are much, much faster than hard disks. Buy one if you can.

In fact, there’s only one disadvantage: price. You’ll still find that ultra-cheap laptops have 500GB or even 1TB (1,000GB) hard disks, yet more expensive ones only have 128GB or 256GB SSDs inside. That’s purely down to price.

What is an SSD? M.2 vs SATA (form factor)

It’s easy to drown in information when it comes to SSDs. Again, abbreviations abound and confusion always sits around the corner. If you really want to understand SSDs, you need to know about two things: the form they come in, and the way in which they exchange data with your computer.

what is an ssd
On the left, an M.2 SSD; on the right. a 2.5in SATA SSD. And now things get complicated…

There are two main form factors: M.2 and 2.5in SATA. I won’t even go into what those letters and numbers stand for because it doesn’t matter. Above, you’ll see a photo of an M.2 SSD (it looks a bit like a stick of memory) and a 2.5in SATA SSD. Quite different.

Note the pics aren’t to scale; that 2.5in SATA drive would be around 25% wider than the M.2 drive.

SSDs: SATA vs PCIe (interface)

Although the previous heading said M.2 vs SATA, that only relates to their physical type. You can actually have SATA M.2 SSDs – take a closer look at the picture above.

A SATA M.2 SSD is one that works over the SATA bus. To be precise, the SATA III bus.

What do I mean by “bus”? In a way, what it sounds like: the means of transport for the data held on your SSD.

The SATA III bus is getting old; it’s Inter-City to bullet trains. To allow your M.2 SSD to fly, it should ideally connect over PCIe (or NVMe, which I cover separately below).

what is an SSD: SATA SSD vs PCIe SSD
Taken from a blog by Dell, this graph shows the performance difference between a SATA SSD and PCIe SSD

PCIe stands for Peripheral Component Interconnect Express and acts like a direct line into the centre of operations. If you see a PCIe M.2 SSD then you should feel confident it will be fast.

Again, though, you’ll pay for the privilege. For most people, a SATA SSD (whether its physical form is M.2 or SATA) is absolutely fine. Having said that, if I was given the option between a PCIe M.2 SSD and a SATA M.2 SSD, I’d always choose the former.

What is an SSD: NVMe

The final thing to look out for is NVMe, which is the fastest type of SSD connection currently available and becoming popular in high-end laptops. It stands for Non-Volatile Memory Express and is essentially the latest evolution of PCIe.

My Surface Book 2 includes an NVMe SSD and is just one of the reasons I love it.

One final note. In your quest for a laptop, you might find Chromebooks that include storage described as eMMC: that stands for embedded MultiMediaCard. However, eMMC storage isn’t the same as SSD storage: it’s cheaper and slower. You only tend to find it in phones and Chromebooks.

About the author

Tim Danton

Tim Danton is editor-in-chief of PC Pro magazine and has written about technology since 1999. He enjoys playing with gadgets, playing with words and playing tennis. Email tim@bigtechquestion.com

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