Best SSD 2015 - The top SSDs for speed and price

Installing an SSD into your laptop or PC can bring it a big new lease of life. SSDs are far faster than traditional hard disks, so programs and even your operating system will load much quicker. Affordable drives are getting bigger and bigger too, so you don't have to sacrifice a lot of storage space in order to switch your old hard disk for a fast SSD in your laptop. In a PC you can keep your current drive for long-term storage and backup, while installing and running all the most important programs off your new SSD. 

The SSDs here were cherry-picked from our recent group test of 25 drives and we've listed prices that are correct at the time of publishing. It's worth shopping about though as prices do vary over time. There are brief reviews of the best SSDs here and below you'll find graphs that compare their overall performance to the other drives in the test.

Crucial MX100 - The Crucial MX100 is a fantastic-value and fast SSD

£90 inc VAT (256GB), £172 inc VAT (512GB) from uk.crucial.com

The MX100 is from Crucial’s budget SSD range, and when it comes to solid performance for a low price, it’s tough to beat. The MX100 is available in 256GB and 512GB capacities, with a low cost per gigabyte of around 35p.

The MX100 uses 16nm 126Gbit/s 2-bit MLC NAND flash sourced from Crucial’s parent company Micron. The smaller 16nm manufacturing process allows Crucial to pack more flash chips into a tighter area, lowering production costs and paving the way for even larger-capacity SSDs, which goes some way to explain how Crucial is able to price the MX100 so competitively. The MX100 uses a Marvell 88SS9189 controller with custom Micron firmware.

Although the MX100 isn’t available as part of an upgrade kit, with all the extras required to fit the SSD inside your PC or laptop, it does come with a couple of extras we wouldn’t expect for a budget model. There’s a spacer for fitting the 7.5mm-thick SSD in a laptop with a 9.5mm drive bay included, as well as a free downloadable copy of Acronis True Image HD 2014. The only critical missing feature, compared to the full retail version of Acronis TrueImage, is the ability to back up only those files that have changed since the last backup instead of all files, which would reduce the time it takes to do a backup. Even so, the included software is useful for copying files from your old hard disk to the MX100.

All Crucial’s MX100 SSDs are rated at 550MB/s read speeds, but write speed performance increases with each higher capacity; the 256GB drive is rated at 330MB/s and the 512GB model at 500MB/s.

We tested the two higher-capacity models and found both performed excellently for the price. The 256GB model had large file read speeds of 457MB/s and write speeds of 454.4MB/s. The faster 512GB model saw read speeds of 467.5MB/s and write speeds of 679.3MB/s. In our small-file tests, the 256GB disk managed a read speed of 81.9MB/s and a write speed of 98.9MB/s. Running the 512GB model through the small-file tests made only a marginal difference to small-file performance.

The 512GB model is worth going for if your budget allows, not only thanks to its better capacity but also its better performance. It’s definitely the sweet spot in the MX100 range. Overall, the MX100 is astonishingly cheap for such a quick SSD, but just loses out to the Sandisk Ultra II for a Best Buy award, due to the Ultra II's similar performance and lower cost per gigabyte.

Crucial M550 - The Crucial M550 has exceptional performance for the money

£110 inc VAT (256GB), £208 inc VAT (512GB), £335 inc VAT (1TB) From uk.crucial.com

The MX100 is Crucial’s budget-friendly SSD, but the M550 exists for those who value extra performance. Unlike Crucial's cheaper model, the M550 is available with up to 1TB of storage. The M550 is the successor to the M500, one of our favourite SSDs. As its name suggests, the M550 is a relatively minor update, but any drive that improves on the excellent M500 is fine by us.

Along with the 1TB drive, you can also buy 256GB and 512GB versions. All except the 1TB model are available as standard 2.5in SATA3 disks and as mSATA DIMM-style chips for use in Ultrabooks. We stuck to testing the 2.5in SATA3 version, but there shouldn’t be any performance differences between the two form factors.

Like the MX100, the M550 isn’t available as part of an upgrade kit with cloning software, a USB to SATA adapter or other accessories. All these bits are widely available elsewhere, though, and a bracket for mounting the 7mm-thick SSD in laptops with 9.5mm disk bays is at least included.

The M550 uses 20nm Micron NAND flash, much like the M500, but with a new Marvell 88SS9189 controller with custom Micron firmware. All the different M550 capacities performed comparably in our file transfer speed tests.

With the 1TB model, large files were written at 617MB/s and read at 618.2MB/s, which are very fast speeds indeed. Small files were written at 100.1MB/s and read at 83.5MB/s, which is above average.  When testing the 256GB model, we saw large-file speeds of 628.5MB/s write and 610MB/s read and 100MB/s write and 81MB/s read in the small files test, so there is little performance difference between the capacities.

The 1TB drive is the best-value drive per gigabyte, costing 38p per GB, but £382 is a considerable amount of money to part with. The 512GB drive is 42p per GB and the 256GB model is 46p per GB, making them both good value for such quick drives.

The M550 isn’t the cheapest SSD, but is still good value and has excellent file transfer performance. It wins a Best Buy award.

Samsung 850 Evo - Samsung’s 3D V-NAND technology makes the 850 Evo a top performer

£110 inc VAT from www.ebuyer.com (250GB)

We were fans of the Samsung 840 Evo series of solid-state drives, as these were the first SSDs we saw to provide capacities up to 1TB. The 850 Evo is the follow-up, and uses Samsung’s new 3D V-NAND technology.

3D V-NAND refers to how the manufacturer stacks the cells in its NAND flash chips both vertically and horizontally, allowing for greater-capacity SSDs without having to shrink the manufacturing process, which is becoming increasingly difficult to achieve. 3D V-NAND chips use a 40nm process rather than the 20nm process more commonly seen in other manufacturers' SSDs.

Although 3D V-NAND should pave the way for higher-capacity SSDs, the 850 Evo range still tops out at 1TB; a similar maximum to rival ranges from Crucial and SanDisk. Samsung does claim that 3D V-NAND has less cell-to-cell interference, which will help the cells last longer, and the technology should lead to higher-capacity SSDs in the future.

The disks in the 850 Evo range all use Samsung MGX controllers, save for the 1TB model, which has a Samsung MEX model. We tested the 250GB, 500GB and 1TB versions of the 850 Evo and performance was almost identically impressive across all the drives.

With the 250GB drive we saw large file write speeds of an astonishing 713.5MB/s. Large file read speeds were less impressive, but still above average at 464.7MB/s. Similarly, the 1TB drive managed a write speed of 712.9MB/s and 465.3MB/s in the large file read test. In our small file test the 1TB drive was the quickest model, with 95.5MB/s write and 99.8MB/s read speeds. Overall small file speeds were around average for all three drive capacities.

There’s no upgrade kit supplied with the drive, nor is one available as an optional bundle. Samsung also hasn’t included a spacer to help fit the drive in 9.5mm-high laptop drive bays, which is a shame. Samsung does provide Samsung Data Migration and Samsung Magician software. The former will make it easy to clone from an existing drive, but you might have to use your own SATA to USB cable if you don’t have a spare SATA cable. Samsung Magician provides a number of useful tools for optimising the disk drive, upgrading the firmware and monitoring the drive's health. The software is straightforward and easy to use.

The 850 Evo’s large-file write speeds are seriously impressive, making this drive a rival for the Crucial M550. The various disks in both drive ranges are a similar price per gigabyte, but the Crucial drive is a faster drive overall, and so just wins out at current pricing.

SanDisk Ultra II - The SanDisk Ultra II is a fast and great-value SSD

£95 inc VAT (240GB), £180 inc VAT (480GB), £340 inc VAT (960GB) From www.mobymemory.co.uk

There aren’t many SSDs that can rival Crucial’s MX100 for value, but the SanDisk Ultra II manages just that, at just 38p per GB for the 240GB drive, 32p per GB for 480GB and an astonishing 30p per GB for the 960GB version. This makes the Ultra II incredible value.

The Ultra II uses a Marvell 88SS9190 controller for the 240GB disk and a Marvell 88SS9189 for the larger capacities. The latter controller is also used by Crucial for its MX100 and M550 SSDs. All the Ultra II drives use SanDisk’s 19nm TLC flash memory, with each cell able to store three bits of data per cell instead of the two in MLC NAND. This means more data can be stored in the same area, allowing for bigger SSDs.

The Ultra II has a SATA3 connector and is 7.5mm thick, so it’ll fit in laptops with slim drive bays designed for single-platter hard disks. A spacer is included for fitting the drive in laptops that require thicker 9.5mm drives.

You don’t get any data migration software bundled explicitly with this SSD, but SanDisk’s SSD Dashboard software is available as a free download. This helps you to monitor and maintain your drive’s health and performance as well as install any firmware upgrades.

We tested the 240GB model, and found its transfer speeds were excellent considering the drive's low price. In our large file read test we saw a 454.4MB/s, which is average, but the drive could write large files at a highly impressive 617.7MB/s, making the Ultra II a top performer for a budget drive. Small file performance was reasonable, with 77MB/s read and 97.5MB/s write. This isn’t quite up there with Crucial's MX100, but it's not far off.

For a long time, the Crucial MX100 was the SSD to beat for those on a tight budget, but the SanDisk Ultra II has stolen its crown. The 240GB model is reasonably priced, but the 960GB version is the best value at just 30p per gigabyte.  

TRANSFER SPEED GRAPHS

To test the read and write speeds of each disk drive, we use a script that copies files to and from the drive and measures the time taken. We copy the files to the disk from memory rather than from another disk drive, because RAM is faster than any hard disk or SSD so won’t act as the limiting factor in the tests. In our large-file tests, we copy a 100MB file to and from each disk 100 times to see how fast a drive is when dealing with big files such as video clips. We repeat this test using a selection of smaller files totalling 100MB, to see how well a drive copes with the many smaller files needed when loading an operating system or application. 

LARGE FILE TEST - READ/WRITE AVERAGE in MB/S

SMALL FILE TEST - READ/WRITE AVERAGE in MB/S