Gadgetory

solid state drives make a big deal out of their marketing language with different initialisms like MLC TLC v-nand 3d v-nand and other sorts of NAND and that's what we're talking about today this is sort of a special edition feature or analysis where we're just strictly going to define what nand is the different types and how they impact you nand and the nand type used in SSDs ties directly into price performance endurance or longevity as it is often known and understanding what nand is and how different functions on the controller work to further endurance or performance that's important to buying an SSD that makes sense for your needs and important to considering the budget restrictions that you might have versus the wants in terms of performance and endurance let's start with an animation that we made for this video this animation highlights a few of the SSDs core components including electrical components like transistors memory components like flash and the driving controller and this as we cut to a simplified SSD image contains a few basic parts there are eight flash modules a controller and eight channels to connect the modules to the controller the controller is effectively the SSDs CPU equivalent and handles all of the transactional processing and we're leveling and garbage collection to ensure that the memory has a lawn service life and when I say memory I do mean flash memory in this instance for sake of example let's talk about a specific type of NAND so one of those might be 16 nanometer flash nand that is of the mlc variety so we'll dive into each of those things mlc means multi-level cell something we'll dive deep with momentarily and NAND flash is the specific type of memory NAND flash is a non-volatile permanent memory sort of an opposite of system Ram which is temporary and volatile and unlike a hard drive everything is sort of transacted at the electron level and without mechanical parts whatsoever then and prefix na nd indicates the type of logic gate used for the flash these gates control the flow of electricity two components has a dam would do for water and if we cut to another simple SSD image here you can see digging a bit deeper that each flash module could contain multiple flash dyes in this case our imaginary SSD saturates all eight of the controllers channels there are eight maximally with this controller and train maximum throughput and it hosts for 128 gigabit dyes per module with eight modules that's 32 dyes at 128 gigabit or 16 gigabytes each for a total of 512 gigabytes of storage after subtracting over-provisioning which we've talked about in previous videos that comes out to what you'd see as a 480 ka SSD so that's the math that's how you get these 512 gigabyte drives or 480 gigabyte drives it's by having die assortments like you've seen in our sample here but what's going on under the NAND there is SLC mlc TLC they're all associated with different performance and endurance metrics and they're targeted at different parts of the market with mlc sort of filling a gap as the affordable but longer-lasting version of NAND with TLC being the 30% cheaper but more capacity but potentially shorter lifespan and and these very hard and fast rules apply in some ways but aren't 100% correct because there's a lot more going on underneath and the controller does dictate just how long a life you can get out of the NAND NAND is spliced into an organization structure to ensure your drive age as well a flash die consists of a few planes normally - which are then broken into blocks let's say there's 1024 of those blocks contain pages a page is the smallest unit of data storage on the SSD generally 16 kilobytes in size before going down to the cell level which is very small the SSD is split in this way because the controller moves data constantly to ensure all the blocks get worn in equally there's a certain lifespan NAND flash can only tolerate so many programs or rights and so many erases collectively called PE cycles before the nand expires and enters a locked read-only state if any block exhausts its p/e cycles unevenly it could jeopardize the entire drive and this is where we could get tangential and talk about controller technology and garbage collection we're leveling and mitigating endurance concerns but we'll do that in a future video every time you write data to your SSD you're actively killing it but the process of we're leveling and relatively high average PE cycle count does mean that most users will exhaust the system's usable life before that of the SSD alone but there's more let's look at the cells cells work at the bit level there are billions of cells in every SSD each responsible for its own bit or bits of data and SLC stands for single-level cell ml c stands for multi-level cell or 2 levels and TLC stands for triple level cell so here's the NAND type for SLC SLC NAND can contain only one bit of data per cell so it's smaller in capacity but faster there are only two possible voltage states for this cell 1 or 0 and when a charge is sent to the cell it returns either a 1 or a 0 for the voltage check a voltage check sees what data if any currently occupies that cell and because there are only two possible voltage outcomes the device runs with greater stability and performance than the more populated multi-level and triple level cells each of which store exponentially more voltage levels and require greater electrical precision at the time of checking this also means that an SLC SSD which is rare to find on the market now would cost more than MLC because MLC can store twice the bits per cell two bits per cell and it does for voltage checks per cell now this means that SLC which is rare to find these days is more expensive than something like an LC and I'll see per gigabyte is cheaper and that's partly because it can fit two bits of data per cell and corresponding with that it's got four voltage levels per CEL we're SLC only had two one and zero TLC then contains three bits of data per cell so it can hold 33% more data per cell as MLC but uses eight voltage levels cost per gigabyte goes drastically down TLC and mlc but there is a speed and endurance trade-off TLC has seven reed points between its voltage levels mlc has three and SLC has one more Reed points means more space for data but greater granularity required at the electrical level for voltage checks the electrical charge of the device weakens as it ages so that extra granularity for TLC voltage checking does mean it will generally become worn out faster than its mlc and SLC counterparts it can store more data per cell as cheaper but that means the cell is being programmed and erased more frequently which also wears it down it's a bit slower as a result of the same voltage checking process but that's a necessity in having an SSD that's the trade-off though for cost and capacity but there's a lot more to it in future videos and actually in past videos we have previously and will in the future talk about over-provisioning and how it's used to lengthen the lifespan of nand of different types talk about write amplification factor what that is you can actually find that in our SSD dictionary on gamers Nexus net if you can expects dictionary at the top and we'll even talk about some of the other controller technologies like garbage collection we're leveling and things of that nature which are all now changing with the advent and push of Faiz on and Marvel controllers into the market as SandForce somewhat becomes obsolete at least its second gen until the fabled third generation maybe one day ships so that's all for this video check out the video and the post role to learn about how SSDs are made in a previous tour of Kingston's factory that we did actually a couple years ago now but it's still relevant and as always patreon like the post roll video subscribe for more information thank you for watching I'll see you all next time