Solid-State Drive (SSD)

Dennis Faas's picture

A solid-state drive (SSD) is a data storage device that uses solid-state memory to store persistent data. SSDs are distinguished from traditional hard disk drives (HDDs), which are electromechanical devices containing spinning disks and movable read / write heads.

SSDs, in contrast, use microchips which retain data in non-volatile memory chips and contain no moving parts.

Solid State Drive (SSD) Compared to a Hard Disk Drive (HDD)

Today's solid state hard drives are considerably faster than a standard (spinning) hard drive.

For example: read / write speeds on a standard HDD are roughly 40-60 megabytes per second sustained. On an SSD using a Sandforce-1200 controller such as an OCZ Vertex 2 SSD, read speeds are 6 times that of a traditional hard drive at blistering 250 megabytes per second. In short, SSDs can dramatically improve upon the speed of a computer's boot and load time.

Compared to traditional HDDs, SSDs are typically less susceptible to physical shock, quieter, and have lower access time and latency. SSDs use the same interface as hard disk drives, thus easily replacing them in most applications.

As of 2010, most SSDs use NAND-based flash memory, which retains memory even without power. SSDs using volatile random-access memory (RAM) also exist for situations which require even faster access, but do not necessarily need data persistence after power loss, or use external power or batteries to maintain the data after power is removed.

A hybrid drive combines the features of an HDD and an SSD in one unit.

Early SSDs using RAM and Similar Technology

The origins of SSDs came from the 1950s using two similar technologies, magnetic core memory and card capacitor read-only store (CCROS).

These auxiliary memory units, as they were called at the time, emerged during the era of vacuum tube computers. But with the introduction of cheaper drum storage units, their use was discontinued.

Later, in the 1970s and 1980s, SSDs were implemented in semiconductor memory for early supercomputers of IBM, Amdahl and Cray; however, the prohibitively high price of the built-to-order SSDs made them quite seldom used.

In 1978, Texas Memory Systems introduced a 16 kilobyte (KB) RAM solid-state drive to be used by oil companies for seismic data acquisition.

The following year, StorageTek developed the first modern type of solid-state drive. The Sharp PC-5000, introduced in 1983, used 128 kilobyte solid-state storage cartridges, containing bubble memory.

In 1984 Tall grass Company had a tape back up unit of 40 MB with a solid state 20 MB unit built in. The 20 MB unit could be used instead of a hard drive.

In September 1986, Santa Clara Systems introduced BatRam, 4 megabyte (MB) mass storage system expandable to 20 MB using 4 MB memory modules. The package included a rechargeable battery to preserve the memory chip contents when the array was not powered.

1987 saw the entry of EMC Corporation into the SSD market, with drives introduced for the mini-computer market. However, EMC exited the business soon after.

Flash-based Solid State Disks

In 1995, M-Systems introduced flash-based solid-state drives. They had the advantage of not requiring batteries to maintain the data in the memory (required by the prior volatile memory systems), but were not as fast as the DRAM-based solutions.

Since then, SSDs have been used successfully as HDD replacements by the military and aerospace industries, as well as other mission-critical applications. These applications require the exceptional mean time between failures (MTBF) rates that solid-state drives achieve, by virtue of their ability to withstand extreme shock, vibration and temperature ranges.

BiTMICRO made a number of introductions and announcements in 1999 around flash-based SSDs including an 18 gigabyte 3.5 in SSD.

Fusion-io announced a PCIe-based SSD with 100,000 input/output operations per second (IOPS) of performance in a single card with capacities up to 320 gigabytes in 2007.

At Cebit 2009, OCZ demonstrated a 1 terabyte (TB) flash SSD using a PCI Express x8 interface. It achieves a maximum write speed of 654 megabytes per second (MB/s) and maximum read speed of 712 MB/s.

In December 2009, Micron Technology announced the world's first SSD using a 6 gigabits per second (Gbit/s) or 768 (MB/s) SATA interface.

SSD Form Factor

The size and shape of any device is largely driven by the size and shape of the components used to make that device. Traditional HDDs and optical drives are designed around the rotating platter or optical disc along with the spindle motor inside.

If an SSD is made up of various interconnected integrated circuits (ICs) and an interface connector, then its shape could be virtually anything imaginable because it is no longer limited to the shape of rotating media drives.

Some solid state storage solutions come in a larger chassis that may even be a rack-mount form factor with numerous SSDs inside. They would all connect to a common bus inside the chassis and connect outside the box with a single connector.

This document is licensed under the GNU Free Documentation License (GFDL), which means that you can copy and modify it as long as the entire work (including additions) remains under this license.

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