SSD compared to HDD – Things you must know. Which is best? Depends on your needs

Today with increasing popularity of SSD drives it is important to understand what they are compared to old HDD drives that have served well for decades and if we really need them. In this article we will dive deep into the world of computer drives and have a look at both SSD drives and HDD drives, including their characteristics, working principles and a little bit more.

The primary application of an SSD drive is exactly the same as of an conventional HDD drive – to store and retrieve the digital information. The difference is in a way how this data is stored.

What is HDD and how they work?
Before we start to look at SSD drives let’s review what is a HDD drive. The hard disc drive (HDD), is a data storage device, that stores data on one or more rotating discs also called platters, that have a coating of magnetic material. By the way the mechanical parts of the drive are the ones that generate the most noise. But the disc is just one part of the whole complex mechanism, there are also other important mechanical components involved in reading and writing process such as: a head, an actuator arm, and an actuator by itself.

How the data is stored to HDDs?
The data is written by changing the magnetization of the specific sections on the disc, where the sequential changes in the direction of the magnetization represent data bits, the digital information is read by measuring the magnetic polarization on the specific sections on the disc. The key thing in reading and writing is the tremendous provisional positing of the head. The head by itself is composed out of the ferromagnetic material wrapped in the wire. The capacity of the HDD drive is greatly depended on the distance between the head and the disc, the closer it is positioned to the drive, the less space is covered by the magnetic field of the head, resulting in more space for digital data. In older drives the head stayed as close as 100nm to the disc, nowadays this distance is around 10nm !

Main properties of HDD
HDD drives can be further characterized by the following primary properties that affect the data transfer rate, they are: seek time, rotating latency, data transfer rate. Other HDD considerations include power consumption, price, noise generated and shock resistance. During reading and writing operations the information is gathered from the specific sections of the disc as previously discussed, but during rotation there is a delay as the reading or writing operation cannot start straight away, because the disc should be at the specific angular position for the operation to be performed.

Seek time is the time taken for the head to travel to the specific location at which the data reading or writing method can be performed. The most common seek time for home desktop computers is somewhere between 9ms-15ms. 

What is Solid State Drive (SSD) and how they work?
What is Solid State Drive (SSD) and how they work?And finally we have reached the part of the article about the Solid State Drives (SSDs), they are drive types that don’t have mechanical parts involved in reading and writing data processes, but instead they use complicated integrated circuits. The technology of that was firstly introduced in the 1950s, and extensively is developed nowadays. Now more and more HDD drives are replaced with SSD drives, with their super fast data transfer rates, with more silent operation, and that is not all, they are also much more resistant to physical shock, a perfect thing for a laptop, isn’t it ? But despite all of these fancy features there are some disadvantages, the main one, of course, is the price, even in the latest 5 years it has been dramatically reduced, the price of SSD drives remain six to seven times higher than HDDs one.

Main parts of SSDs
There are three main parts of a SSD drive: NAND cells, NAND controller, and a HostInterface.
The digital data in SSDs is stored in a large arrays of cells, every single cell might store even more data, depending on drives technology. If it is a single level cell (SLC), then each cell can store only one bit, if it is a multi level cell (MLC), it might store either 2 bits or even more, there are drives that are able to store 3 bits per cell, sometimes they are called a triple level cell (TLC), more commonly found on SSD drives that use PCI connection. The more cells there are, the higher densities can be achieved, but this comes with the decrease in writing and reading speeds.

NAND controller communicates with the host device and manages the flash life system, it also does some error correction, bad block mapping, encryption and other essential things. Wear leveling is also done by the controller, as NAND cells have a limited number of write cycles, it is important to perform some manipulations to prolong the SSD drive service life.

An SSD drive is definitely a great thing for a computer, as it won’t just speed it up, but also provide a safe place where to store your precious data.

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