Solid-state drive

A solid-state drive or solid-state disk (abbreviated SSD; borrowed from English), more rarely also called a semiconductor drive or solid-state memory, is a non-volatile data storage device in computer technology. The term drive refers to the original and common definition for this medium of computers. The design and electrical connections may or may not conform to the standards for drives with magnetic or optical disks. They can, for example, also be designed as PCIe plug-in cards. If a magnetic hard disk drive HDD) is combined with a solid-state memory to form a device, this is known as a hybrid hard drive (HHD; also solid state hybrid drive, SSHD).

Solid-state drives were developed in the course of the second half of the 20th century until they became capable of mass use beyond individual applications. Their costs were initially very high in relation to the storage capacity, but just like the sizes, they quickly decreased in accordance with Moore's Law for the same performance, so that they also became economically viable for special uses around the turn of the millennium. Nevertheless, the prices for SSDs (in euros per gigabyte) were still several times the price of a conventional magnetic storage drive in July 2018. At the beginning of 2021, the price was still around four times that of a commercially available hard disk of the same capacity.

SSDs have no moving parts and are therefore insensitive to shocks, jolts and vibrations. They also have shorter access times and operate silently. Unlike hard disks, an SSD does not need any start-up time after start-up. It requires less power and produces less waste heat. SSDs can be built much smaller than equivalent storage with magnetic disks. Failures and errors of SSDs are often caused by errors in the firmware, which always comes to the market immature and is only later improved by updates. SSD memory cells also have a limited number of write cycles.

Term

In electronics, the English term "solid state" means that semiconductor components are used. This distinguishes them from other storage technologies such as core memories, punched cards or memories with moving mechanical parts such as rotating magnetic disks. In analogy to drive technologies such as HDDs, FDDs and ODDs, the medium is referred to as a "drive".

Development and history

Early SSDs

Solid-state drives originated in the 1950s with two similar technologies, magnetic core memory and Charged Capacitor Read-Only Storage (CCROS), an early form of read-only memory. These supporting forms of storage appeared in the era of electron tube computers, but were then abandoned by the advent of less expensive drum storage.

In the 1970s and 1980s, SSDs were implemented in semiconductor memories of the early supercomputers from IBM, Amdahl and Cray, but were rarely used due to their very high price. In the late 1970s, General Instruments introduced Electrically Alterable ROM (EAROM, another form of read-only memory), which had close similarities to later NAND flash technology. However, since the lifespan of this memory was less than ten years, the technology was abandoned by many companies. In 1976, Dataram started selling a product called Bulk Core, which delivered up to 2 MB of solid-state memory compatible with Digital Equipment Corporation (DEC) and Data-General (DG) computers. In 1978, Texas Memory Systems introduced a 16-kilobyte RAM solid-state drive to be used by oil production companies to record seismic data. The following year (1979), StorageTek developed the first RAM solid-state drive.

The Sharp PC-5000, introduced in 1983, used 128-kilobyte solid-state cartridges that used magnetic bubble memory. In 1984, Tallgrass Technologies Corporation introduced a 40-MB backup unit with an integrated 20-MB SSD that could alternatively be used as a disk drive. In September 1986, Santa Clara Systems announced the BatRam: a 4 MB mass storage system that could be expanded up to 20 MB. The system included rechargeable batteries to provide power to the chip when the power supply was interrupted. In 1987, EMC Corporation installed SSDs in mini-computers for the first time, but discontinued this development in 1993.

flash-based SSDs

In 1983, the Psion MC 400 Mobile Computer shipped with four slots for removable memory in the form of flash-based solid-state disks. These slots were of the same type used on the Psion Series 3 for flash memory cards. These modules had the major disadvantage that they had to be formatted each time in order to free memory from deleted or modified files. Old versions of files that were deleted or edited continued to take up memory until the module was formatted.

In 1991, SanDisk introduced a 20MB solid-state drive that sold for $1000. In 1995, M-Systems introduced for the first time a flash-based solid-state drive that did not require batteries to retain data. However, it was not as fast as DRAM-based solutions. From that point on, SSDs were successfully used as HDD replacements by military and aerospace organizations.

In 1999, BiTMICRO introduced several products in the field of flash-based SSDs, including an 18 GB 3.5-inch SSD. In 2007, Fusion-io introduced a PCIe-based SSD with a performance of 100,000 IOPS in a single card with a capacity of up to 320 GB. In 2009, OCZ Technology unveiled a flash SSD at Cebit that had a maximum write speed of 654 MB/s and a maximum read speed of 712 MB/s with a capacity of one terabyte (using a PCIe-x8 interface). In December of the same year, Micron Technology announced an SSD that would use a 6 Gigabit SATA interface.

enterprise flash memory

Enterprise flash drives (EFDs) are designed for applications that require high IOPS performance, reliability and efficiency. In most cases, an EFD is an SSD with a richer set of specifications compared to a standard SSD. The term was first used by EMC in January 2008 to identify SSD vendors that provided products with these higher standards. However, there are no standards or rules that distinguish EFDs from SSDs, which is why in principle any manufacturer can state that they produce EFDs.

In 2012, Intel introduced the SSD DC S3700 - an EFD designed to deliver consistent performance. This field had previously received little attention.