How we tested SSDs and others we tested
SSDs make your whole system faster and more pleasant to use. But they matter for gaming, too.
A fast-loading SSD can cut dozens of seconds off the loading times of big games like Battlefield 4, or MMOs like World of Warcraft. An SSD won’t affect framerate like your GPU or CPU, but it will make installing, booting, dying and reloading in games a faster, smoother process. When shopping for a good SSD for gaming, one of the most important factors is price per gigabyte. How much will you have to spend to keep a healthy library of Steam games installed, ready to be played at a moment’s notice?
To find the best gaming SSDs, we researched the SSD market, picked out the strongest contenders, and put them through their paces with several benchmarking tools. We also put in the research to know what makes a great SSD great, beyond the numbers—technical stuff like types of flash memory and memory controllers.
To be clear,
this article only covers 2.5-inch SATA SSDs, the standard internal drives most PC gamers are accustomed to. There are newer, faster SSD form-factors (M.2 and PCie) that can deliver far greater performance than SATA drives. But right now, there are very few of them, motherboard support is limited, and they tend to be far more expensive than SATA SSDs. M.2 will likely be much bigger by 2016, and we’ll update this article when appropriate.
To test the SSDs, we used a PC with a 4GHz Intel Core i7-4790k, 16GB of DDR3 memory, an Nvidia GeForce GTX 970 graphics card, and an Asus Z87 motherboard. Windows 7 was installed on the main system drive, AHCI was enabled, and all the drives were connected to the motherboard’s SATA III ports.
We used a combination of synthetic and trace benchmarks. This included AS SSD, CrystalDiskMark, and PCMark08, which runs a set number of timed traces of popular applications.
The single specific advantage that makes an SSD so much faster than a hard disk is exponentially shorter access time. A hard disk depends on a mechanical arm moving into position to read data from a platter, while in an SSD, data is stored and accessed electronically. Although modern hard disks are astonishingly fast at accessing data, they’re no match for an SSD.
An SSD is a physically simple device. It’s made from an array of flash memory chips and a controller, which comprises a processor, memory cache, and firmware. But like most things in computing, it starts to get complicated when you look at it in more detail. NAND flash chips store binary values as voltage differences in non-volatile memory, meaning they retain their state when power is cut off. In order to change the state of a single cell, in effect, writing to it, a strong voltage is applied to it. But because of the way the cells are laid out, it can’t be done on a cell-by-cell basis: an entire row has to be erased at once.
Each cell is insulated from its neighbours to preserve the value it holds. But every time a cell is written to, the insulator becomes slightly less reliable. Eventually, after a certain number of writes, the cell becomes unable to hold any values, which is why SSDs have a limited lifespan. In the early days of flash memory, this limited number of writes was a concern, but clever tricks, improved technology, and software improvements means it’s no longer a real issue.
If you want further proof, then have a gander at the SSD endurance experiment over on TechReport. In one of the only tests of its kind, they set about continuously writing data to select SSDs, until the drives became completely unusable, in a test that went on for months. Although the odd bad sector crops up relatively early, at 100TB of writes, most of the drives survived until nearly a petabyte of data or more was written to them, far beyond the manufacturers’ rating, and it took months of non-stop writing to reach that point.
The best drives managed 2.5 PB of writes. It’s fair to say endurance for all but the most extreme workload is no longer an issue.
SLC, MLC, and TLC memory
A given quantity of physical flash memory cells can be programmed to hold either one, two or three bits of data. A drive where each cell holds a single bit is known as SLC. Each cell can only be in one of two states, on or off, and only needs to be sensitive to two voltages. Its endurance and performance will be incredible but a large amount of flash memory is needed to provide a given capacity, so SLC drives have never really taken off beyond expensive server and workstation setups.
2-bit MLC memory is currently the most popular kind used in consumer SSDs. Each cell holds two values, with four binary states (00, 01, 10 and 11), so the cell needs to be sensitive to four voltages. The same amount of flash memory provides double the amount of space, so less is needed and the SSD is more affordable.
3-bit TLC memory goes even further, with three values per cell. Now each cell has to hold eight binary states, and performance and endurance begins to really suffer as there are eight distinct voltages that represent data. A TLC cell will be erased more often, and therefore wears out quicker. And since it needs to hold eight voltage values, reading them reliably requires more precision. But you get even more capacity from the same amount of flash memory, resulting in even cheaper SSDs, which is something everyone wants.
As we’ve found from testing some SSDs, manufacturers are using tricks to mitigate these negative effects with TLC flash memory, so prices can continue falling without impacting performance.
Sequential Transfer Speeds
Whenever you read about an SSD, or look at a review, the first figure you’ll usually see is a headline-grabbing transfer rate. Read and write speeds up to around 500MB/sec, or even faster in the case of a PCI-Express SSD. These numbers always look really impressive. This will certainly be referring to sequential file transfer rates, which means the speed a storage device can read or write a file if all the blocks are laid out one after the other.
In the real world, most software applications deal with both large and small files, while at times, a program might be waiting for input before it carries on, so you’ll never be getting the maximum sequential speed of your SSD all the time. You might see these speeds when writing a large 10GB movie file, but things will be a lot slower when copying a folder full of 10,000 jpeg images, or HTML documents. These smaller files could be spread all over the disk, and will be slower to transfer.
In the case of a hard disk, that entails moving the disk head over the correct position on the platter, which adds a really long delay. SSDs are far quicker to do this, which is where the real improvement in overall responsiveness comes from.
To further complicate things, some SSDs handle uncompressed data much faster than compressed data. Specifically, there has been a big difference in performance with these two types of data with SSDs that use older SandForce controllers. If there’s a difference, the faster speeds when dealing with uncompressed data are the ones that are quoted. Therefore, although faster sequential speeds are always better to see, it’s best not to judge an SSD on these figures alone, as you’ll never get these speeds all the time.
IOPS is another term that is often used in relation to performance of storage products, usually quoted with SSD specifications, but its direct application to real-world use isn’t simple. Put simply, IOPS means input-output operations per second. The more a device can manage, the faster it is. Except, not all IO operations are the same. Reading a tiny 512-byte text file isn’t the same thing as writing a 256KB block from a 10GB movie.
There’s no standard for how figures should be advertised, but the general agreed format is that companies quote the QD32, 4KB block size figure, that is the IOPS when 32 4KB read or write commands are queued. In the real world, applications won’t be constantly queuing up 32 4KB blocks. It will likely be a random mixture of block sizes, reads, writes, and times when the storage device is idle.
Much effort goes into measuring IOPS for patterns that simulate databases, web servers, file servers and so on. For gaming, it really depends on the application, since no two games will be identical. Some might involve huge textures being loaded from disk, while others might be structured differently. Although the 4K QD32 IOPS figure is relevant, it’s best thought of as an indicator of SSD performance rather than a definitive, comparable benchmark for overall performance.
We narrowed our testing down to 9 SSDs by researching the most popular and competitive drives around. Of course, there are plenty of other SSDs out there, and new ones arriving regularly, like the OCZ Vector 180, which may end up being a good competitor for the high-end Samsung 850 Pro. We focused on SSDs known to be reliable, consistent performers, and the best value options.
Looking at the benchmark results, and particularly the PCMark08 traces, it’s not exactly obvious that one SSD seriously outperforms another in real-world tests. Even the differences between drives in synthetic benchmarks are fairly narrow, with differences of ten percent or so. Even if you buy an SSD that’s not included in our testing, it will be far faster than a mechanical hard drive—it just might not quite match the speed and endurance of a drive like the Samsung 850 EVO.
At the high end, it seems clear that the SATA bus is now the serious limiting factor in SSD performance. Fortunately, SSD manufacturers can take advantage of the PCI-Express bus, and much faster speeds, with a new standard called M.2, which I’ll explain in a moment.
But even the affordable SSDs are really good. Sure, they might be a bit slower in synthetic benchmarks, but in real-world tests, you’ll find little reason to complain about their performance.
For the entry-level choice, it was a close call between Crucial’s BX100 and the SanDisk Ultra II. As of this writing, the Ultra II has a lower retail price, but it’s based on TLC flash, and it came out ever so sightly lower in the benchmark results. We went with Crucial’s offering, but if you end up with an Ultra II in your PC, you won’t be disappointed. OCZ’s Arc 100 is also absolutely fine, but its retail price pushes its price per GB slightly above Crucial and SanDisk’s SSDs.
Intel’s 730 series SSD has been on the market a while, and has been surpassed by the firm’s PCI-Express 750 series drive, which is a lot more up to date, but frankly, we’d ignore the 730, for its pricing is just not good value for money, and its write speeds suffer compared with Samsung, Crucial, or Plextor’s drives.
Similarly, Kingston’s V300 is a bit old now, and it too has similarly poor synthetic write results and wasn’t quite as good, despite its affordability.
At the high end, Samsung’s competition comes from Plextor’s M6 Pro and SanDisk’s Extreme Pro (which we unfortunately didn’t get a sample of for testing). 3D NAND is definitely the future, as it makes a big difference to performance and endurance, and Samsung certainly has an advantage here. The Magician software helps too: it’s the best SSD software going, and its Rapid Mode feature works well. Samsung might not have this advantage forever. Just recently, Intel and Micron announced a partnership to develop 3D NAND, with 48-layer chips coming soon, although products might not be with us until 2016. Intel promises SSDs with up to 10TB of capacity, thanks to this extra chip density, which admittedly sounds quite amazing, and is likely to cause serious concern for hard disk manufacturers.
For the best choice for an SSD, we chose Samsung’s SSD 850 EVO because it both performs superbly and is excellent value for money. In fact, the price per GB of the 500GB 850 EVO model works out better value than any of the 256GB drives. Being based on TLC flash memory doesn’t seem to hold it back at all, and 3D NAND clearly makes a big difference to performance.
However, it’s worth pointing out that Crucial’s MX200 gives it a run for its money, and is better value too for the 256GB model. It certainly qualifies as a close runner up.
Now that an SSDs are such good value, there’s simply no reason not to have one for your PC. If you were an early adopter with a 64GB or 128GB drive and find that capacity to be rather limiting, it might be time to consider an upgrade. A 512GB SSD now costs a lot less than a 128GB model did a few years ago.
Future testing: M.2, PCI-Express and NVMe
Standard 2.5-inch SSDs are fundamentally limited by the speed of the SATA III bus, which has a maximum theoretical throughput of 6 Gbit/sec. In real world terms, the performance ceiling is around 550 MB/sec for an SSD, and it’s becoming obvious that this is imposing a serious limit on flash memory technology.
The solution is to switch to the PCI-Express bus, which offers 500 MB/sec per lane, with a x4 card allowing for up to 2 GB/sec. But unfortunately, all PCI-Express SSDs to date are really expensive, and being in a PCI card format is quite limiting. You may have issues fitting one in a tiny case, and you can’t transfer it to a laptop if you upgrade your desktop PC in the future, for example.
There are alternatives: SATA Express runs at 10 Gbit/sec, a small improvement, and for ultra-thin laptops, there’s mSATA, which runs at the same speed as SATA III but reduces the size of the SSD.
What’s on the horizon looks promising: a new format called M.2, which can use either the PCI-Express, USB or SATA bus and squeezes the size of SSDs down even further. If you have an up-to-date motherboard with an Intel Z97 or X99 chipset, you’ll probably have one of these slots. It’s less probable that you actually own an M.2 device though.
The size of M.2 devices is denoted with a number, specifying the card’s width and length. For SSDs, this is normally 22mm wide and either 60mm, 80mm or 110mm long. Unfortunately, the number of M.2 SSDs on the market is quite slim right now. And many of them use the old SATA bus rather than take advantage PCI-Express.
But times are changing, and there are some really promising new models on the horizon. One example is Kingston’s Hyper X Predator, which runs at PCI-Express x4 speeds, and comes in an interesting package. A PCI card is supplied with an M.2 connector on it, so you can just plug it into any old desktop PC motherboard. If you have an M.2 slot, or a computer (like a laptop) without PCI-Express slots, the SSD can be removed from the card and plugged in. A neat idea. Plextor’s M6e is one of the only affordable current x2 PCIe models, and Plextor will have a follow-up x4 drive in 2015, too.
There’s another old standard that’s holding back SSD performance: AHCI. The original host protocol for communicating with storage devices was designed at a time when everyone used hard disks, and certain assumptions were made regarding latency and performance. It limits what can be done with SSDs. AHCI has now been replaced by NVMe, which lifts those limits. For example, the maximum number of IO commands has gone from 32 to 65536. Booting from NVMe is not supported by the vast majority of motherboards, however. Only newer boards enable it, again based on Intel’s latest chipsets.
Some NVMe SSDs are starting to hit the market. Intel’s brand new PCI Express 750 series is one such SSD, and from early reviews it seems to be a lot faster than any 2.5-inch SATA SSD. We’ll be checking out PCIe and M.2 SSDs as they become available.
In another 10 years, solid state technology may make today’s SATA SSDs look like floppy disks. But for now, SATA SSDs still offer the best performance you’re going to get for your dollar, and the Samsung 850 EVO is currently the best choice for a great gaming SSD.
A note on affiliates: some of our stories, like this one, include affiliate links to stores like Amazon. These online stores share a small amount of revenue with us if you buy something through one of these links, which helps support our work evaluating PC components.