What is SSD (Solid State Drive)?

What actually is SSD? SSD itself is a modern and quick hard-disk technology. However, precursors of SSDs have existed since the 1950s, and the actual SSD storage has been around since 1970. The solutions at that time were extremely expensive, had a low life expectancy, and lost their contents when run without power supply (volatile data storage).

It was not until the 1990s that the first flash-based SSD came onto the market, which retained the data once stored independently of the power supply, i.e., it was non-volatile. In addition to flash modules, SDRAM memory modules were also used – primarily as intermediate storage – which were volatile but significantly faster than conventional RAM. Industrial SSDs currently achieve storage capacities of up to 100 terabytes with 5 million write cycles and a guaranteed data retention of up to 10 years. They are used, for example, on servers with SSD.

The abbreviation ‘SSD’ stands for ‘Solid State Drive’. The term ‘solid state’ refers to the semiconductor components; ‘drive’ is the term for the drive – in other words, ‘drive made of semiconductor components’. The term ‘solid state drive’ isn’t really used much. An SSD is therefore an arrangement of loads of semiconductor elements that are used by a file management system to store digital data. For organising data on a SSD, the file management systems FAT32 and NTFS are used – how this is done is explained in separate articles.

In an SSD, the information stored is written to semiconductor cells. These cells retain their status even when there is no power supply – the principle of flash memory. A single memory cell can only have two states: charged or uncharged. This method is called Single Level Cell (SLC) and is mainly used in very expensive, industrial SSDs. One cell corresponds to one bit which illustrates how many such cells are needed to realise one gigabyte (1 GB), for example 10⁹ = 1 billion memory cells (exact value: 2³⁰ = 1,073,741,824). A single letter in ASCII coding alone consumes 8 bits. That might give you an idea of how much memory is needed for a text document or for images.

However, it is also possible to use different voltage sizes in one cell so that more than 1 bit can be stored per memory cell. This type of storage is called Multi Level Cell (MLC) and usually allows 2 bits per cell. So, more data can be accommodated in the space and it works out more cost-effective. Its disadvantage is the lower number of write cycles. Another compression step is called Triple Level Cell (TLC), which further reduces manufacturing costs.

Semiconductors have a limited lifespan. To counteract this, an SSD has internal monitoring that detects worn memory cells. This Bad Block Management marks cell blocks with declining memory cells as faulty and replaces them with cells from a reserve stock. Depending on the SSD design, this comprises two to seven percent of the total storage capacity and considerably extends the usage life of an SSD.

Hybrid hard disks (HHD), however, shouldn’t be forgotten. This is a combination of an HDD hard drive and SSD. The fast flash memory of the SSD can increase the overall speed of such a hybrid compared to normal HDDs but doesn’t come close to that of single SSDs.

The good comes with the bad, but there aren’t many bad sides to SSDs.

A striking advantage of SSDs are their short data access times, which are around one hundredth of the time of HDDs. In addition, there are much higher data transfer rates for reading and writing. A SSD requires no start-up time and has no mechanical components (apart from the connectors for connection). In addition, this technology is shock and vibration resistant, has a low energy requirement which means there is less inherent heat. The volume-to-storage space ratio is also better and SSD operation is quiet which lots of people will appreciate.

SSD hard drives are (still) significantly more expensive than conventional hard drives and the number of read-write cycles is limited due to the properties of the semiconductors used. SSD drives are also sensitive to very high temperatures.

You can find more information about the advantages and disadvantages of the conventional hard drive and the SSD in our guide SSD vs. HDD. You can find out more about the Shingled Magnetic Recording process for increasing the storage density in magnetic storage media in our article on SMR.

In the private sector, ever more devices are equipped with SSDs. These include laptops, PCs, digital cameras, or digital music players. In PCs, SSDs are often installed as system disks for the operating system and programs, while a (often much larger) HDD stores work data. Smartphones and tablets usually have a shorter use life than non-mobile devices, so these are ideal candidates for the use of SSDs. All these devices benefit from the low weight, speed, and shock resistance of the SSD. The lower pricing of SSDs suggests that all storage solutions in the private sector will be equipped with SSDs in the future.

Professional or industrial applications are mainly high-performance servers like the IONOS server with SSD, as future-orientated storage solutions. However, high-end laptops or desktops are also equipped with SSDs. In addition, this storage technology is used where large amounts of information have to be provided in (near) real-time. This includes aerospace – flight recorders, for example – but also military settings.