Storage Devices
HARD DRIVES
The term hard drive refers to the large-capacity onboard storage found in either desktop or laptop computers. Magnetic hard drives are also known as hard disk drives (HDDs). HDDs have one or more magnetized platters mounted on a spindle and spin at high speeds past read/write heads Speeds The speed at which the magnetic media spins has a great deal to do with drive performance and its suitability for a specific task. Table 16.1 compares the common speeds found in recent internal HDDs and what each speed is best used for.
Speed Form factors Interface Best Use
5,400rpm 2.5 in, 3.5 in SATA General computing
7,200rpm 2.5 in, 3.5 in SATA High-performance PCs; NAS; enterprise network storage
3.5 in SAS Enterprise network storage
10,000rpm 3.5 in SATA High-performance PCs
2.5 in, 3.5 in SAS SCSI* Enterprise network storage
15,000rpm 2.5 in, 3.5 in SAS SCSI* Enterprise network storage
rpm=revolutions per minute
SATA=Serial Advanced Technology Attachment
NAS=Network Attached Storage
SAS=Serial Attached SCSI
SCSI=Small Computer System Interface (parallel)
* Parallel SCSI drives have capacities of 300GB or less, making them suitable primarily for maintaining legacy network storage
Small Computer System Interface (SCSI) is a series of standards for connecting multiple devices (HDDs, tape drives, printers, scanners, and others) to a single host adapter. SCSI devices use parallel connections.
Serial Attached SCSI (SAS) is a modern version of SCSI that uses high-speed serial connections while continuing to use SCSI protocols. SATA drives can be connected to SAS ports.
HDD Form Factors
In computers, form factor refers to the physical shape and dimensions of a component such as a hard drive, power supply, or motherboard. There are two form factors used in HDDs.
2.5-inch drives
3.5-inch drives
The dimensions refer to their width (see Figure 16.2). Each size is optimized for different uses. Let’s take a closer look, focusing on SATA (internal) and USB (external) interface drives.
SSDs
Solid-state drives (SSDs) use high-speed, high-capacity nonvolatile memory, typically NAND, and are designed for use as a system or data drive in place of HDDs. SSDs have largely replaced HDDs as system drives in laptops. SSDs are also used as system drives in midrange and high-end desktop computers.
Solid-state
drives have much faster boot times, faster read speeds, and faster write speeds than HDDs. However, SSDs are more expensive per gigabyte, so HDDs continue to be useful for data storage. Consequently, many systems use SSDs for boot drives and HDDs for data drives.
SSD Form Factors
SSDs are available in three form factors.
▶ SATA
▶ M.2
▶mSATA
Let’s learn about the differences among them next.
SATA
SATA SSD drives connect to the same power and data cables as SATA HDDs but use smaller
2.5-inch
drive bays (adapters enable these drives to fit into 3.5-inch
drive bays as well).
These drives are faster than SATA HDDs, but the M.2 form factor (next section) drives are
much faster than any SATA interface drive.
M.2
M.2 drives, originally known as next-generation
form factor (NGFF) drives, are about the
same size as a memory module but have contacts on one end instead of on one side. An
M.2 drive slides into a small surface-mounted
connector on a laptop (or desktop) motherboard
and is held in place by a set screw at the opposite end of the drive.
M.2 drives are available in various form factors, the most common of which are as follows:
2280 (22mm wide, 80mm long)
2242 (22mm wide, 42mm long)
2230 (22mm wide, 30mm long)
M.2 is an interface that is also used by various types of communication cards, and the
M.2 interface connectors on motherboards are keyed according to the device types they
accept. M.2 drives use either SATA or NVMe communications interfaces. Figure 16.6 compares
an M.2 SSD card with a wireless M.2 card.
Quiz to practice
