Currently within this category, only the HDD or SSD on which the OS is installed can be considered as main hardware . There are also hybrid applications known as hybrid hard drives or SSHD, but their use is not widespread.
HDDs or hard drives are storage elements that use an electromagnetic data accumulation system. The information is recorded on a rotating disk known as a platter thanks to the action of the read and write head.
HDD capacity is larger than other storage devices. Currently there are 20 terabyte models, although the 4, 6 and 8 TB corresponding to the previous generation are more common.
Apart from capacity, there are other characteristics of HDDs that should be known:
Error rates and firmware correction . The more resistant the system is to the introduction of errors in the accumulated bits, the greater the reliability of the component. Today many hard drives use code to alleviate writing errors. Thus, a protected partition of the hardware is assigned for Error Correction Codes (ECC), Low Density Parity Checks (LDPC), or proprietary software from manufacturers.
Rotational speed . It measures the number of revolutions per minute of the disk. Modern models use engines up to 7200 rpm. At higher rotational speed; faster reading and writing speed, electrical consumption, noise produced and physical wear and tear.
Search time, rotational latency and data transmission speed . They affect the speed of reading and writing. The first two are physical impediments to the hard drive structure; they depend on the position of the platters to be read and the location of the read / write head. The data transmission speed acts as a bottleneck when the connectors are inadequate.
Form factor . This is a ratio of the size of the HDD envelope. We have to choose a form factor that can be docked without problems in our tower or laptop.
Connection interfaces and buses . The buses used by contemporary computers are of the type ATA, Serial ATA (SATA), SCI, Serial Attached SCI (more commonly known as SAS) and Fiber Channel or FC.
Auxiliary equipment . They are components that are an inseparable part of the HDD: temperature sensors, filters, adaptations for demanding atmospheres …
HDDs have been used in desktops, laptops, and consumer electronics not only to accumulate information, but also to install the operating system and software that is used on a daily basis. However, in recent years a new technology based on flash memory has begun to displace this element in its most basic function, that of hosting the OS.
We are talking about SSDs or solid state drives. It is a persistent storage that improves several properties of traditional HDDs : they are silent, they do not have moving parts that can degrade with use, their read and write speed is higher, and their latency is lower. Its only drawback is the price, and it continues to drop.
SSDs are made up of controllers, the memory unit, a cache or buffer, a battery or supercapacitor, and an interface for connection to the computer . The controller is one of the most relevant elements since the number of NAND chips that make it up establishes the speed of reading and writing of the device.
The SSD supports around a million rewrites. Depending on the range accessed, it is equipped with non-volatile NAND flash memory or triple, quad or multi-level cell flash memories (TLC, QLC and MLC) which are cheaper and have worse performance. There are also items on the market with memories based on DRAM, 3D Xpoint (Intel and Micron technology), NVDIMM (Hyper DIMM) and ULLtraDIMM. The speed of the SSD depends on the type of memory used; the best option is DRAM.
The available data transfer interfaces are: SAS, SATA, mSATA, PCI Express, M.2, U.2, Fiber Channel, USB, UDMA (or Parallel ATA), and SCSI.
In general, SSDs are more robust, more durable and faster, hence they are the preferred option today .