The difference between SLC, MLC, TLC and QLC NAND SSD: which is better?

If you want a top-level system , Especially for game or content creation , that SSD be absolutely necessary . However , Before you go looking , You should know what to look for . There are many different types SSD. Just basic SSD For storage units , Yes SLC、MLC、TLC and QLC. among ,TLC Is the most popular , however ,QLC Will eventually replace them . stay I/O aspect , Yes SATA and NVMe.

Last , Abreast of the times SSD Also based on 3D NAND/VNAND technology . This may make  SSD Choices become very confusing . Let's break down these terms .

SLC、MLC、TLC and QLC： These are storage units

stay HDD in , Tracks are building blocks of memory . stay SSD in , The same functions are provided by the unit , The unit is essentially a gate circuit . How much can be stored in each unit depends on SSD Unit type used . The most popular is SLC、MLC、TLC and QLC, These represent single-layer units 、 Multilayer cell 、 Three layer unit and four layer unit .

seeing the name of a thing one thinks of its function ,SLC SSD Only one bit can be stored in each cell ,MLC Store two ,TLC Store three ,QLC Store four . Although this seems to be a “ The bigger the better ” The situation of , But this is not the case . Use QLC Drive increases capacity （ At the same price ） It's the easiest , Because for the same amount of storage , The number of units they need is SLC The driver's 1/4.

Bigger is not always better

Writing multiple bits to a single cell takes more time , It will also affect SSD The durability of . It means SLC SSD It's actually the fastest and most reliable , But they are much more expensive . Most commercial SSD by  TLC, It's in performance 、 A reasonable compromise is provided between reliability and cost .

The number of times a unit can be read and written before it stops working is limited .  This usually has the scale of hundreds of thousands of reads and writes , be called TBW（ Total bytes written ）. However , It means SSD The availability of is limited , Maybe a few years . Now ,SLC The drive hardly exists ,MLC Limited to a few high-performance data centers .

TLC Is the most popular , And 3D NAND It can be used together in performance 、 There is a very good balance between durability and price .QLC Now it's popular , Although it still lags behind in speed and durability TLC, But it's cheaper . This leads to many OEM In prefabrication PC Use them in , therefore , Before buying , Be sure to check the durability of the drive （TBW Or maximum write TB）, And compare it with others based on TLC Compare the options of . Even if the drive （ Crashed ） During the warranty period , If exceeded TBW value , The supplier may also refuse to replace .

connectivity ：SATA And NVMe： What is? M.2？

You may already be in SSD and HDD Note these terms in the description of . They look terrible , But it's not really terrible . Two of them only refer to the type of input connector used ,SATA It is both a connector and an interface , This is an old legacy standard , All traditions HDD All use it .

The main limiting factor is SATA The maximum transmission rate of is 600 MB/s. This is right HDD It's not a problem , Because their maximum speed is lower than 200 MB/s. however SATA SSD Will be much slower than its theoretical maximum speed . On the other hand ,NVMe SSD Its maximum reading speed easily exceeds 3,500 MB/s, and PCIe Gen 4 The drive reaches 7,000 MB/s. Besides , be based on SATA The drive of can only perform one function at a time , Read or write , Not both . be based on NVMe Of M.2 SSD Sure .

SATA and NVMe Another major difference between is command queuing or parallelism .SATA Depend on Advanced host controller interface (AHCI), It can handle 32 Pending commands . On the other hand ,NVMe Maximum allowed 64,000 A queue , Each queue can have at most 64,000 An order  . meanwhile , Because of its simpler complexity and direct implementation ,NVMe Than SATA Take up less CPU resources .

NVMe It works very similar to multi-core processors , Divide longer tasks into smaller blocks , These blocks require less time and can run in parallel . It can be 32 Queue depth of up to 440,000 Random reads IOPS and 360,000 Random write times IOPS performance .

The downside is , Of every system NVMe SSD Limited number , Because most consumer PC Medium PCIe The number from 16 To 24 Unequal ,GPU Use... At most 16 individual , The network adapter uses a pair . This is a desktop PC Upper 2-3 individual NVMe The drive leaves space . by comparison , Most medium and high-end PC It can easily accommodate up to 8 individual SATA SSD.

M.2 Just a relatively new connection type . It plugs directly into the... On the motherboard M.2 slot , Can be connected to SATA or PCIe Bus .M.2 SATA SSD Smaller and thinner , But it can still provide SATA Speed . meanwhile ,M.2 NVMe SSD Through the... On the motherboard PCIe Channel connection , And smaller 、 Thinner and faster . If you want the fastest storage ,NVMe SSD, adopt M.2 Connection is the way to go .

3D NAND and VNAND： These are layers

What happens when there is no room left around you ？ This is basically 3D NAND What we did . Traditionally ,NAND Unit with 2D Mode arrangement , The more units , The larger the drive capacity （ The memory of each chip increases ）. But as the demise of Moore's law tells us , The extent to which silicon chips can be shrunk is limited .

therefore , because 2D There are no cells in , We began to stack them one by one , This is called 3D NAND. It's not only cheaper , And faster , And more energy-saving . Manufacturers will usually be based on TLC and QLC Of SSD And 3D Stack or VNAND pairing , To further improve the cost performance , Make the drive more affordable .

Samsung VNAND Technology is theirs 3D NAND edition , There are some proprietary modifications .

Higher density SSD Basically, it has a higher number of layers . Now , As many as 96 Layers of units are stacked between consumers and businesses SSD in . expect 100 layer NAND The estimated density of the chip is 1Tb.