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Or how to look like you know what you’re talking about
NAND flash is a type of nonvolatile flash memory that stands for "Not And," which is a reference to the type of logic gate it uses. This is different from NOR flash, which is used in environments where the same program is run over and over again. NAND memory is popular due to its speed, durability, and relatively low cost compared to DRAM, and is commonly found in storage devices such as USB keys, tablets, cell phones, and of course, SSDs. Though there are various types of NAND flash, all SSDs on the market currently use this type of memory.
This is the brains of the SSD and what truly separates one drive from another, as they mostly use very similar NAND flash. Typical controllers today use multiple cores for running the drive, performing data compression, and executing drive optimizations. Before you make any purchasing decisions about an SSD, find out which controller it uses, as some controllers have a checkered history. Currently only Samsung and OCZ have controllers that were designed and manufactured in-house, which theoretically gives them an advantage, while Intel uses SandForce, Corsair uses Link A Media, and Crucial uses a Marvell controller.
This is the most common type of NAND flash used in SSDs today, and it stands for “multi-level cell” memory. Its much more expensive counterpart is SLC, or “single-level cell” memory. In SLC, only one state can be maintained per cell, making it good for one bit of data. In MLC, however, up to four states can be stored per cell, allowing it to hold two bits of data. The proximity of the two states creates the possibility for more errors, though, which is why SLC is so expensive, and rare. Flash memory can only sustain a finite number of read/write operations but modern day SSDs perform wear-leveling in order to allow them to survive for a decade or longer depending on drive activity levels.
This is the good stuff. SLC NAND is very expensive and is only found in enterprise-level storage products due to its cost. It stores one data state per cell, and since there are no other data states nearby, it is extremely accurate and long-lasting. At press time a 256GB SLC SSD costs $2,600, so you won't be seeing them in your home machine any time soon.
Trim is something you'll hear about a lot with SSDs, because it performs the crucial function of helping the SSD optimize itself when it is idle, so not having Trim support is bad, and it needs to be in both the drive and your OS. Essentially, the Trim command is sent from the OS to the drive's controller to tell it which bits of data can be safely deleted, so without Trim the drive could theoretically just fill up and degrade. Since NAND cells cannot be overwritten, they must be erased before new data is written to them. The command also lets the controller reorganize data, similar to defragmenting a hard drive. Trim is supported in Windows 7 and 8, and in all modern SSDs.
You'll see this in an SSD's specs, and the bottom line is that asynchronous flash is not as fast or expensive as synchronous flash, so it's not uncommon to see it in value drives, while synchronous flash is used in high-performance drives. Synchronous flash processes data roughly twice as fast as asynchronous, on both ends of the clock cycle, so you get two outputs per cycle, while asynchronous is not synced to the clock speed of the processor, so you can expect lower performance.
This spec shows how many operations per second the drive is capable of performing. This differs from read/write speeds in that it's not measuring the speed of the writes or reads, but the number of them. This is typically used in situations where heavy random workloads are needed, simply because, in our opinion, it sounds better to say 85,000 IOPS than 30MB/s.
This is how fast a drive can read and write contiguous data, sort of like an elephant inhaling a row of peanuts. This is often used as a metric for benchmarks because it measures "straight-line speeds" but is not indicative of real-world performance, as data is rarely written or read in this fashion.
Old blocks of data on an SSD have to be erased before new blocks can be written to it, which takes time, so the fastest an SSD will ever be is the moment it comes out of the box and is totally empty. Unfortunately, even if you deleted everything on the drive, the data is still there, so it will still need to be erased if you want to write over it (Trim does this to some extent but not completely). The only way to totally wipe a drive of all its contents is a Secure Erase, which completely deletes all data on a drive. This is the most common way to get an SSD back to its fastest possible state, and is accomplished via software included with your drive.
See the next page to read about the downside of using Trim and to learn about different SSD software.