An SSD is the single best and simplest upgrade you can make to any PC or laptop without replacing the processor or graphics card. In this guide, we'll explain the technology, the choices you'll have to make and then run through the best nine (three of each type) choices.
In the very simplest terms, an SSD (solid-state drive) performs exactly the same function as your regular hard disk (or hard drive, if you prefer) but much, much faster. It replaces the mechanical aspects of your hard disk with non-moving transistors. They're more expensive that hard disks, but the performance benefit they offer is absolutely worth it. Read on for even more detail:
SSDs' performance advantage is most acutely felt when it comes to access time. This is the time it takes for the drive to move from one bit of data to another. Traditionally, it's where hard drives struggle the most, since data is stored on a spinning disk with a read head that physically has to move back and forth across the disk to find the data.
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With SSDs there’s no such physical movement, and as a result access times are vastly better. For instance, while a hard drive will have an access time of around 15ms, an SSD will take only 0.1ms.
This advantage is reflected in random read and write speeds, which is what makes SSDs feel so quick. While a hard disk will struggle to achieve 1MB/sec random read, a typical SSD will easily hit 20MB/sec. Whether loading Photoshop or a new section of a game, it's an SSD’s short sharp bursts of data access that make it such a great upgrade.
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When it comes to moving large chunks of data – sequential read and writes – an SSD maintains an advantage but not to the same degree. A typical hard drive can hit around 125MB/sec read and write, while a decent SSD will hit 500MB/sec read and write.
In fact, one area that separates the really fast drives from the lesser ones is sequential write speed, with the cheaper drives managing only around 200MB/sec. Meanwhile, the fastest PCI Express and PCI Express M.2 drives can hit 1,500MB/sec read and write.
You can also buy external USB SSDs, such as the Samsung Portable SSD T3
In this guide, we’ll be exploring three types of SSD: SATA, M.2 and PCI Express. We’ll explain the differences and provide you with the best three in each category that we’ve tested.
SSDs are made from small memory chips called NAND – named after the negative-AND logic gates. They’re broadly similar to the silicon used to build RAM, although the chips used in SSDs can store data after a PC is turned off – a crucial difference between SSDs and more volatile memory.
Drives are made from several of these NAND chips in formation. Over the past few years, SSD firms have experimented with precisely what type of memory to use, but they’ve now largely settled with something called multi-level cell, or MLC.
The three drives in this test all use MLC memory, which makes it the clear winner over single-level cell or SLC chips – even though both types of memory have pros and cons. MLC chips are far cheaper than SLC chips, but their denser data arrangement means their lifespan is poorer and write speeds can be worse.
Whichever way you look at it, there’s a trade-off; and firms are working to combat MLC’s weaker points. SSDs now use wear-levelling techniques to ensure that chips deteriorate at the same speed, and redundant areas on SSDs can be used to replace failed cells.
Those future-proofed features all come from the controller, which is another crucial SSD component. These tiny chips manage the flow of data in and out of the SSD, as well as handling consistency and preservation features. In addition, a high-quality control chip goes a long way to determining the speed and reliability of an SSD.
This is what an SSD looks like on the inside. Data is stored on the larger 'NAND' chips in the centre (image: Samsung)
Controllers are a mixed bag: some are made by the SSD manufacturers themselves – Intel, for example – but some cheaper drives used third-party chips from manufacturers such as Marvell and Phison. No matter the maker, controllers are accompanied by a cache of DDR memory – usually up to 512MB.
What should you look for when buying an SSD?
Your first port of call should be the capacity, since this figure will determine just how much space you’ll have to play with. It’s even more important with SSDs, because most of these drives don’t match hard disks for size versus price.
Most consumer SSDs range between 120GB and 512GB, with pricier drives now available in sizes up to around 1TB. The classic combination of a smaller capacity SSD for loading up with Windows and your games, matched with a large hard drive for all your bulky data such as music, pictures and video, is still likely to be the best option for many users.
However, prices are falling now to the point where one 512GB drive might be affordable and still provide sufficient space.
Also bear in mind that the stated capacity of an SSD won’t be available once it’s installed; formatted capacity will be reduced, as is the case with all forms of storage.
Another consideration is the endurance rating, which is a useful guide to how long the SSD will last. If you’re buying for a home or gaming PC, virtually all consumer drives will last for years. If your new SSD is for a PC, where huge amounts of data will be repeatedly written to the drive (a video-editing machine, for example, where you’ll be loading the files onto the drive for editing then removing them again), then look for a higher rating.
Other attributes are also worth a look if you’re buying for the office. Many SSDs come with encryption and error protection that can help protect vital data. These features significantly increase cost, though, so if they’re not required then stick to the budget options.
SATA SSDs are the most common type of SSD, and probably the ones with which you’re most familiar. They use the SATA 3 standard – also known as SATA 6Gbps – and connect to your motherboard using the same SATA cables as your standard hard disk. This limits their overall speed, but for most people SATA SSDs provide the best bang-for-buck performance, and are always the cheapest option.
The form factor is worth investigation: the vast majority of SATA-based drives are of the 2.5in variety and the majority now adhere to the slimmer 7mm design. However, a few drives – especially older models – adopt the chunkier 9.5mm blueprint. This is unlikely to have an impact on most desktop PCs, but it could mean a drive might not fit inside certain laptops.
Pay attention to what comes in the box, too. Some SSDs don’t come with any extras, but others come with spacers, screws and even kits to adapt them to larger PC drive bays.
Once your drive is installed, first check for any available firmware updates. These can fix bugs and improve performance and reliability, but often can't be done without loss of any data you've already copied over.
These drives exploit the huge bandwidth provided by PCI Express slots to deliver speeds several times quicker than any SATA-based drive. That makes them enormously tempting for anyone with a need for speed: gamers can load the latest titles faster; work applications boot with added speed; and any PC can benefit from lightning-fast loading times.
The speed of PCI Express SSDs isn’t down to the use of faster memory chips; the PCI bandwidth means that silicon can be accessed far more rapidly.
The older SATA interface was designed for slower hard disks and was then retro-fitted to work with SSDs, so it’s no surprise that the burgeoning SSD market has outgrown this archaic connection. SATA connectors are comparatively simple, with a relatively low-bandwidth ceiling.
PCI Express works differently. Each PCI connector is constructed from a number of lanes, each with its own bandwidth for data transfer in both directions. All PCI-based SSDs use connectors with four lanes, which means eight lanes of data flowing back and forward – so there’s ample bandwidth for any SSD drive; far more than a single SATA connector can provide.
It also helps that most motherboards and PCIe SSDs now use the third iteration of PCI Express, because this more modern standard stretches its lead even further over SATA. PCIe drives also benefit from NVMe – a new interface that’s specifically designed for SSDs that connect using PCIe. It’s a standardised option that brings speed and reliability improvements to the fore.
On paper, then, PCI connectors are far more capable and versatile than SATA ports – and the raw numbers do a great job of demonstrating just how much extra bandwidth is available.
A PCI Express 3.0 connector with four lanes can deliver bandwidth of 1GB/sec per lane per direction – so a PCI Express 3.0 4x connector can deliver a maximum bandwidth of 8GB/sec. That’s a far cry from SATA, which tops out at 600MB/sec.
It’s worth bearing in mind that these figures for PCIe SSDs are largely theoretical, because the chips themselves can’t saturate that 4GB/sec throughput figure. But it means there’s more than enough bandwidth for any current SSD and ample headroom for future drives.
The numbers make PCI Express the clear winner – and there are other reasons too why it’s about to supercede SATA. The older connector requires a huge amount of engineering to move beyond single-lane transfers, to the point where a new connector would be required. And if that’s the case, just move to PCI Express – it’s already on most motherboards.
Look beyond the different connector, and the hardware that underpins PCI-based SSDs is the same as SATA-based drives.
The change in interface leads to aesthetic differences between PCI and SATA SSDs. Older drives were hamstrung by their 2.5in form factor, with many drives arriving in bland metal cases.
The PCI Express cards now used for SSDs allow firms a little more creative freedom, although few seem to have exploited this to any significant degree yet. Intel’s drive is a bland metal box, and Kingston’s expansion card shows off the M.2 drive at the heart of the predator. Zotac’s SSD is the best I’ve seen so far – its metal shroud is decorated with neat oval cut-outs.
The emergence of PCIe SSDs has also given rise to a selection of accessories. It’s now possible to buy PCI Express cards with M.2 ports on-board, which means those M.2 drives can be adapted to fit into a PCIe 4x slot.
Buying an adapter card won’t make the M.2 drive any faster, but it remains an option if you have a motherboard that doesn’t have an M.2 connector, or would like to move to a board without one. An adapter card can be used to deploy a lightning-fast drive such as the Samsung 950 Pro, even if you don’t have an NVMe-enabled M.2 port.
Many PCI Express SSDs also arrive with a half-height blanker that replaces the full-size piece of metal at the end of the drive. It’s a crucial part if any PCIe SSD is going to be installed into a smaller enclosure.
Most of these drives plug and play without much fuss, but there are a couple of points worth bearing in mind when running NVMe hardware. Not all motherboards properly support booting from NVMe drives, so check if you’d like a PCIe SSD to be your main drive. Check drivers, too – Microsoft’s operating systems from Windows 8.1 forward have pre-installed NVMe drivers, but some firms provide better proprietary software.
The M.2 standard replaces the mSATA connections that had previously found favour in Ultrabooks, laptops and even some desktop PC motherboards. The new M.2 specification is far more versatile, as modules can support a wider variety of hardware: Wi-Fi cards, NFC add-in modules, satnav cards and, of course, SSDs are all popular.
Cards that use this interface can be different sizes too: full-length 80mm boards are most frequently used for storage, while squat 42mm cards usually contain wireless chips. That means they can fit in the tiniest of spaces and laptops – and that they’re always smaller than traditional SSDs.
The M.2 interface is versatile because it supports three interfaces: PCI Express 3.0, SATA 3.0 and USB 3.0. That PCI interface is important, because it unlocks far faster speeds than any SATA drive can manage – and it’s further bolstered by NVMe, which is a new interface specifically designed for SSDs, bringing a large boost in performance.
How to use an M.2 SSD
Installing an M.2 SSD is easy, as simple as slotting the drive into the connector and attaching one screw. However, getting to the drive on a laptop can be more complicated and it’s important to make sure a new drive is compatible with existing hardware.
For a desktop PC, you’ll need a motherboard with either Intel’s Z97 or X99 chipset – but even then, there could be restrictions. The Intel Z97 chipset – which is used on mainstream motherboards with the LGA 1150 socket – reserves only two PCI lanes for M.2 drives, which means that bandwidth tops out at 1GB/sec.
That’s ample for M.2 drives based on SATA, since they won’t get near that figure, but it’s enough to bottleneck PCI-based drives. Only a few motherboards have got around this problem, but they do so by borrowing PCI lanes from elsewhere, which means some PCI slots don’t work to their full potential – in particular, dual-graphics is less viable.
The best way to ensure the full PCI M.2 experience right now is to use a PC with an Intel X99 chipset. That means an LGA 2011-v3 processor and an expensive Haswell-E part, with prices ranging from £260 for the i7-5820K to a whopping £690 for the i7-5960X.
That’s a lot of money to spend, but it does mean that you’ll be able to use the fastest PCI-based M.2 SSDs, since the X99 chipset gives the drives four PCI lanes with enough bandwidth to avoid bottlenecking any current M.2 SSDs.
Many laptops – especially gaming notebooks – are now deploying M.2 drives, and larger models often come with spare slots for future upgrades. Laptop chipsets don’t have as many PCI lanes as their desktop counterparts, though, so check a model before buying; it’s no good investing in an expensive drive that can’t run at its full speed.
The drawbacks of M.2 SSDs
Support for M.2 drives on Intel boards is restricted to recent, high-end hardware, but it’s still a better picture than AMD. The new storage standard isn’t supported natively by AMD, so motherboard manufacturers have to reroute PCI or SATA lanes from elsewhere in order to offer M.2 sockets – and, even then, they usually only get two lanes rather than four.
Most Intel and AMD hardware involves compromise unless you drop plenty of cash – and that’s not going to change in the immediate future. AMD hasn’t announced future plans involving M.2, but we’d bet that superior support is included in its future chipsets. Intel’s Skylake platform and its Z170 chipset will support up to four M.2 interfaces, but it isn’t scheduled to appear until the autumn.
If you have an older machine, or a motherboard that doesn’t support fast M.2 drives, then there’s hope for you yet since PCI cards can be used to add M.2 support for older machines. Some of these can be bought as standalone products, but others – such as the Kingston HyperX Predator drive we’ve reviewed in this group – arrive with cards in the box.
Benchmark applications AS SSD and CrystalDiskMark run each drive through a variety of tests. Their sequential read and write routines test the raw file-copying pace of each drive, while a variety of random read and write tests demonstrate how responsive the drive is to the more random use a drive is put through during day to day use – the “snappy” feel of an SSD is all about its random read access performance.
ATTO’s benchmark also tests the read and write pace of each drive, but it uses an even larger variety of file sizes, which adds further detail to the picture of how each SSD will perform.
All the prices used here are accurate at the time of writing.