A hard
disk drive (HDD), is an electro-mechanical data storage device
that stores and retrieves digital data using magnetic storage with one or more rigid rapidly
rotating platters coated
with magnetic material. The platters are made from a non-magnetic material,
usually aluminum alloy, glass,
or ceramic. The platters are paired with magnetic heads,
usually arranged on a moving actuator arm, which read and
write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data
can be stored and retrieved in any order. HDDs are a type of non-volatile storage,
retains stored data when powered off. Modern HDDs are typically in the form
of a small rectangular box.
The two most
common form factors for modern HDDs are 3.5-inch, for desktop computers, and
2.5-inch, primarily for laptops. HDDs are connected to systems by standard interface cables
such as PATA (Parallel ATA), SATA
(Serial ATA), USB or SAS (Serial Attached SCSI)
cables, and Fibre Channel.
Introduced
by IBM in 1956, HDDs were the dominant secondary storage device for general-purpose
computers beginning in the early 1960s. HDDs maintained this
position in the modern era of servers and personal computers, though personal computing
devices produced in large volumes, like mobile phones and tablets, rely on flash memory storage devices.
In the 2000s
and 2010s, NAND flash-based SSDs began supplanting HDDs in applications
requiring portability or high performance. NAND performance is improving faster
than HDDs, and applications for HDDs are eroding. The highest-capacity HDDs
shipping commercially in 2022 are 26 TB, while the largest capacity SSDs
had a capacity of 100 TB. HDD unit shipments peaked at 651 million units
in 2010 and have been declining since then to 166 million units in 2022.
Advantages of SSDs
over Traditional spinning platters
A solid-state
drive (SSD) is a solid-state storage
device that uses integrated circuit
assemblies to store data persistently,
typically using flash memory and
functions as secondary storage
in the hierarchy of computer
storage. It is also sometimes called a semiconductor storage
device, a solid-state device, or a solid-state disk, even
though SSDs lack the physical spinning disks and
movable read-write heads
used in hard disk drives
(HDDs) and floppy disks. SSD also
has rich internal parallelism for data processing. Solid-state drives (SSDs) have higher
data-transfer rates, higher areal storage density, somewhat better reliability,
and much lower latency and access times.
Flash-based
SSDs store data in metal–oxide–semiconductor
(MOS) integrated circuit
chips which contain non-volatile floating-gate memory cells.
Flash memory-based solutions are typically packaged in standard disk drive form
factors (1.8-, 2.5-, and 3.5-inch), but also in smaller more compact form
factors, such as the M.2 form factor, made possible by the small size
of flash memory.
The key
components of an SSD are the controller and the memory to store the data. The
primary memory component in an SSD was traditionally DRAM
volatile memory, but since 2009, it has been more
commonly NAND flash non-volatile memory.
Every SSD includes a controller
that incorporates the electronics that bridge the NAND memory components to the
host computer. The controller is an embedded processor
that executes firmware-level code and is one of the most important factors of
SSD performance.
In
comparison to hard disk drives and similar electromechanical media which use
moving parts, SSDs are typically more resistant to physical shock, run
silently, and have higher input/output rates and lower latency. SSDs
based on NAND flash will slowly leak charge over time if
left for long periods without power. This causes worn-out drives (that have
exceeded their endurance rating) to start losing data typically after one year
(if stored at 30 °C) to two years (at 25 °C) in storage; for new
drives, it takes longer. Therefore, SSDs are not suitable for archival storage. SSDs have a limited lifetime
number of writes and also slow down as they reach their full storage capacity.
Due to the
extremely close spacing between the heads and the disk surface, HDDs are
vulnerable to being damaged by a head crash – a failure of the disk in which the head scrapes
across the platter surface, often grinding away the thin magnetic film and
causing data loss. Head crashes can be caused by electronic failure, a sudden
power failure, physical shock, contamination of the drive's internal enclosure,
wear and tear, corrosion, or poorly
manufactured platters and heads.
Most of the
advantages of solid-state drives over traditional hard drives are due to their
ability to access data completely electronically instead of
electromechanically, resulting in superior transfer speeds and mechanical
ruggedness.
Flash
memory as a replacement for hard drives
The size and
shape of any device are 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(s)
or optical disc along with the spindle motor
inside. Since an SSD is made up of various interconnected integrated circuits
(ICs) and an interface connector, its shape 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. As of 2014, mSATA
and M.2 form factors also gained popularity,
primarily in laptops.
M.2
form factor, formerly known as the Next Generation Form Factor (NGFF), is a
natural transition from the mSATA and physical layout it used, to a more usable
and more advanced form factor. While mSATA took advantage of an existing form
factor and connector, M.2 has been designed to maximize usage of the card
space, while minimizing the footprint. The M.2 standard allows both SATA and PCI Express SSDs to be fitted onto M.2 modules. The
SSD was designed to be installed permanently inside a computer.
Due to their
generally prohibitive cost versus HDDs at the time, until 2009, SSDs were
mainly used in those aspects of mission-critical applications where the speed of
the storage system
needed to be as high as possible. Since flash memory has become a common
component of SSDs, the falling prices and increased densities have made it more
cost-effective for many other applications. For instance, in the distributed computing
environment, SSDs can be used as the building block for a distributed cache layer that temporarily absorbs
the large volume of user requests to the slower HDD-based backend storage
system. This layer provides much higher bandwidth and lower latency than the
storage system and can be managed in a number of forms, such as distributed key-value databases
and distributed file systems. On
supercomputers, this layer is typically referred to as a burst buffer. With this fast layer, users often
experience shorter system response times. Organizations that can benefit from
faster access to system data include equity trading
companies, telecommunication
corporations, and streaming media and
video editing firms. The list of applications
that could benefit from faster storage is vast.
Flash-based
solid-state drives can be used to create network appliances from general-purpose
personal computer
hardware. A write-protected flash
drive containing the operating system and application software can substitute
for larger, less reliable disk drives or CD-ROMs. Appliances built this way can
provide an inexpensive alternative to expensive router and firewall hardware.
SSDs based on
an SD card with a live SD
operating system are easily write-locked. Combined with
a cloud computing
environment or other writable medium, to maintain persistence,
an OS booted from a write-locked SD card is robust,
rugged, reliable, and impervious to permanent corruption. If the running OS
degrades, simply turning the machine off and then on returns it back to its
initial uncorrupted state and thus is particularly solid. The SD card installed
OS does not require removal of corrupted components since it was write-locked
though any written media may need to be restored.
One source
states that, in 2008, the flash memory industry included about US$9.1 billion
in production and sales. Other sources put the flash memory market at a size of
more than US$20 billion in 2006, accounting for more than eight percent of the
overall semiconductor market and more than 34 percent of the total
semiconductor memory market. In 2012, the market was estimated at $26.8
billion, it can take up to 10 weeks to produce a flash memory chip. Samsung
remains the largest NAND flash memory manufacturer as of the first quarter 2022.
Technology
assessment (TA,
German: Technikfolgenabschätzung, French: Évaluation des choix scientifiques
et technologiques) is
a practical process of determining the value of a new or emerging technology in
and of itself or against existing technologies. This is a means of assessing
and rating the new technology from the time when it was first developed to the
time when it is potentially accepted by the public and authorities for further
use. In essence, TA could be defined as "a form of policy research that
examines short- and long-term consequences (for example, societal, economic,
ethical, legal) of the application of technology."
TA is the
study and evaluation of new technologies. It is a way of trying to forecast and
prepare for the upcoming technological advancements and their repercussions on society, and then make decisions based on the judgments. It is based on the
conviction that new developments within, and discoveries by, the scientific
community are relevant for the world at large rather than just for the
scientific experts themselves and that technological progress can never be
free of ethical implications. Also, technology assessment recognizes the fact
that scientists normally are not trained ethicists themselves and accordingly ought to be
very careful when passing ethical judgment on their own, or their colleagues,
new findings, projects, or work in progress. TA is a very broad phenomenon
that also includes aspects such as "diffusion of technology (and
technology transfer), factors leading to rapid acceptance of new technology,
and the role of technology and society."
Technology
assessment assumes a global perspective and is future-oriented, not
anti-technological. TA considers its task as an interdisciplinary approach to
solving already existing problems and preventing potential damage caused by the
uncritical application and commercialization of new technologies.
