What are SSDs?

Solid State Drives are now becoming popular but more importantly, cheaper. So lets tackle the question, what are SSDs?

An Solid state drive is a type of device that uses flash memory to store data permanently. It usually functions as a secondary memory for PCs and tertiary storage in general. SSDs are used to store data until it is needed.

They are called Solid State Drives because unlike a Hard Disk Drive (HDD) or floppy disk, they have absolutely no moving parts. HDDs and floppies have a spinning disk that saves information. In order to read them, the disk has to be spun so that the read/write head can read them. The entire SSD on the other hand, is a single solid package that can store and retrieve data electronically without any moving parts.

A brief history of SSDs

Flash based Solid State Drives which we all now use were invented in 1991 by SanDisk. Even though flash memory was invented by Toshiba earlier, SanDisk were quick to sniff its potential and quickly commercialized it. The first SSD on offer was a 20MB SSD in 1991.

All that being said, the first SSD that was purpose made for computers (desktops and laptops) was introduced by M-Systems in 1995. SanDisk would buy M-Systems in 2006.

Types of SSDs

Generally speaking, there are two types of: commercial and enterprise. Commercial SSDs are meant for the general public while enterprise SSDs are high end SSDs used by companies and organizations.

Parts of an SSD

Generally speaking, there are three main parts that you should care about.

  1. Controller
  2. Interface/connection
  3. Memory

What are SSDs?


A memory controller is an embedded microprocessor that executes firmware code which helps a solid state drive do its job.

Controllers help to connect (or allow) the host CPUs interface with the flash memory. Controllers are very important for SSD performance. In fact, SSDs are only as good as their controllers. This is why solid state drives with NVMe controllers seems to have been dominating the market.

Other functions of the controller includes:

  1. checking for bad blocks
  2. read/write caching
  3. encryption/decryption of data
  4. wear leveling
  5. garbage collection etc.


The connector or interface is where the SSD plugs into the host computer. It serves two main purposes. The first is to allow data flow in and out of the solid state drive to the host computer. It also to provides the electricity needed for the SSD to run.

There are several types of interfaces used by SSDs today. These include:

  • SCSI (12Gbps)
  • SATA/mSATA (6Gbps)
  • PCIe (31Gbps)
  • M.2, U.2 and fibre (128Gbps)
  • USB (10Gbps)
  • PATA/PSCSI (extinct)


This is the memory that holds all of the stored data on a solid state drive. There are different types of memory used to store data on SSDs, these include: NAND, DRAM, 3D Xpoint, NVDIMM etc. The most popular however is NAND flash.

There are three types of SSDs based on NAND flash. These are SLC, MLC and TLC.

If you want to buy an SSD secondary storage or a laptop, you may come across these terms.

  • SLC stands for single layer cell. These are memory cells that only store one bit of data.
  • MLC or multi layer cell can store two bits of data.
  • TLC can store three bits.

TLC is mostly used because it can store a lot more data cheaply. Most of the 1TB and 2TB SSDs you see around are TLC SSDs. TLC SSDs are cheap but they’re slower than other SSDs because it may take a while for the memory controller to locate data.

MLC SSDs cannot store as much data as TLC SSDs but they can hold a good amount of data and they’re also fairly priced. MLC SSDs offer a good balance between storage, performance and price because they are much faster than TLC SSDs.

Lastly you have SLC SSDs. These ones are the fastest SSDs based on NAND flash memory. They are really fast and have excellent performance but they hold less data and are really really expensive. They are also more reliable and last longer than the other two types.

SSD performance

Another thing you should also know is that when it comes to SSD performance, most companies will throw sequential reads and write speed at you. Those aren’t really important for performance at all.

Seq. read/write are only important for data transfer. Especially when you’re moving huge amounts of data like from a laptop to a phone.

For performance, the right spec to look at is the random read/write speeds. This is how the SSDs handle stuff like CPU data request, CPU data writes, caching etc.

SSD manufacturers

Some of the key companies that manufacture SSDs commercially include Western Digital, Samsung, SanDisk, Seagate, Asus, Dell, SK Hynix, Intel, Kingston, Kioxia, Micron, TDK, Toshiba etc.

SSD specs that you should care about

  • Capacity
  • Controller type
  • Random read/write
  • Sequential read/write
  • Memory type
  • Connection/interface

To put this all together, an ideal SSD should be a 1TB NVMe NAND SSD with random read/writes (400k IOPS), seq. read (10GB/s), seq. write (6GB/s) and a PCIe 4.0 connector.

Still confused? Read the article again. This time, slowly. Cheers.

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