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.