Storage Devices | CompTIA A+ 220-1001 | 3.4

In this video you will learn about storage devices such as: optical drives, solid-state drives, magnetic hard drives, hybrid drives, flash drives, & various storage device configurations.

Optical Drives

In computing, an optical drive is a disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to or from optical discs by way of continuous spirals of indentations called pits and lands that are burned into the non-label side of the disc from the middle outward to the edge.

There are 3 main categories for optical drives:

  • CDs: such as CD-ROM, CD-R (recordable CD), and CD-RW (rewritable CD).
  • Blu-ray: such as BD-ROM, Combo BD-ROM/DVD Super Multi, BD-R, and BD-RE.

Optical drive capacities:

  • Blu-ray (highest capacity): uses a blue laser with a shorter wavelength than DVD or CD.
  • DVD: uses a red laser with a longer wavelength than Blu-ray but shorter than that of CD.
  • CD (lowest capacity): uses a near-infrared laser with the longest wavelength.

The differences in laser wavelengths for each optical drive determines the storage capacities for Blu-ray, DVD, and CD optical drives.  The shorter the wavelength, the smaller the pits and lands on the disc — and shorter wavelengths enable more data to be stored in the same space.


A CD-R is a compact disc that can be written once and read many times but data cannot be deleted. 80-minute CD-Rs have a capacity of 700MB, whereas the older 74-minute CD-Rs have a capacity of 650MB. A CD-ROM (read-only memory) is a pre-pressed optical compact disc that contains data. Computers can read CD-ROMs but not write to or erase the data on them. A CD-RW is a compact disc that can be written, read, erased, and rewritten to (up to 1,000 times). CD-RWs have a capacity up to 700MB but depending on how the disc is formatted, it can be less.

Four types of CD-RW media:

  • CD-RW 1x-4x
  • High-speed CD-RW 4x-12x
  • Ultra-speed CD-RW 12x-24x
  • Ultra-speed+ CD-RW 32x

Drives compatible with faster media types can usually work with slower media types but not the other way around.

DVD Recordable and Rewritable Standards

A DVD (digital versatile disc or digital video disc) is a digital optical disc data storage medium that can store any kind of digital data and is widely used for software and other computer files as well as video programs watched using DVD players. DVDs offer higher storage capacity than CDs while having the same dimensions.

DVD-R and DVD+R media is recordable but not erasable, whereas DVD-RW and DVD+RW media uses a phase-change medium similar to CD-RW and can be rewritten up to 1,000 times.

DVD media types you need to be concerned with for the CompTIA A+ 220-1001 examination:

  • DVD-ROM: A read-only DVD commonly used for storing large software applications. It is similar to a CD-ROM but has a larger capacity. A DVD-ROM stores around 4.38GB of data, whereas a CD-ROM stores around 650MB of data.
  • DVD-RW: A single-sided rewritable/erasable media similar to CD-RW which has a capacity of 4.7GB. DVD-RW drives can also write to DVD-R media.
  • DVD-R DL:  A single-sided writable/nonerasable media similar to CD-R but with a second recording layer; it has capacity of 8.4GB.

Blu-Ray (BD)

Blue-ray disc is a digital optical disc storage format designed to supersede the DVD format, capable of storing several hours of video in high-definition (HDTV 720p and 1080p). The main application of Blu-ray is as a medium for video material such as feature films and for the physical distribution of video games for gaming systems. The name “Blu-ray” refers to the blue laser (actually violet) used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs.

Blu-ray media types you need to be concerned with for the CompTIA A+ 220-1001 examination:

  • BD-R:  Recordable, not erasable, similar to CD-R, DVD±R, DVD-R; 25GB capacity.
  • BD-RE:  Recordable and rewritable; similar to CD-RW, DVD-RW, DVD+RW.  25GB capacity.

Note that CD & DVD media are also compatible with Blu-ray drives.

Hard Drives (HD)

Solid-State Drive (SSD)

An SSD is a type of mass storage device similar to a hard disk drive.  It supports reading and writing data and maintains stored data in a permanent state even without power.  SSDs are rapidly becoming the system drive of choice for laptops and convertible computers as well as for performance-oriented desktop computers and servers.  These drives use various types of high-performance flash memory to store files, and they can be used for the operating system, apps, and data. Because there is no need to move read-write heads to various storage areas of the drive to locate data, SSDs are faster than mechanical hard drives and are not affected by shock. SSD is currently more expensive with less capacity than HDD, but SSD capacity is improving, and costs are dropping. An SSD is typically 2.5 inches wide, but some made for very small laptops are available in a 1.8 inch wide form factor.  Most SSDs connect to the motherboard with SATA interfaces. When any type of SSD is used, an internal or external hard drive can also be used to provide additional storage for apps and data.

Typical SSD

M.2 Drives

M.2 (pronounced “M-dot-2”) is an SSD (that looks like a RAM chip) that conforms to a computer industry specification and is used in internally mounted storage expansion cards of a small form factor. In layman’s terms, M.2 SSDs can be mounted directly onto a motherboard or an expansion card thereby giving the drive more direct access to the CPU for faster reading than is possible with an SSD. In order to mount an M.2 SSD, the motherboard must be specifically designed to accept an M.2 SSD, meaning, older systems are more than likely not going to be able to utilize an M.2 SSD.

Typical M.2 SSD


A solid-state hybrid drive (SSHD) is a logical or physical storage device that combines a faster storage medium such as solid-state drive (SSD) with a higher-capacity hard disk drive (HDD).  The intent is adding some of the speed of SSDs to the cost-effective storage capacity of traditional HDDs. The purpose of the SSD in a hybrid drive is to act as a cache for the data stored on the HDD, improving the overall performance by keeping copies of the most frequently used data on the faster SSD.  A SSHD resembles a standard HDD, but it also includes up to 8GB of high-speed flash memory. An SSHD is a combination HDD and SSD, offering up to 4TB of storage that can be accessed several times faster than with an HDD. SSDs are more expensive than spinning disk drives, however, they have many advantages over their rivals such as:  SSDs use smaller form factors so they can fit into smaller spaces, they run cooler, and they are much faster than spinning disk drives.

Comparison of Various types of Hard Drives


NVM Express is an open logical-device interface specification for accessing non-volatile storage media attached via the PCIe bus. The acronym NVM stands for non-volatile memory, which is often NAND flash memory that comes in several physical form factors, including SSDs, PCIe add-in cards, M.2 cards, amongst other forms. NVMe, as a logical-device interface (not a physical form factor like M.2 nor an interface like PCIe; but can be used with both M.2 & PCIe), has been designed to capitalize on the low latency and internal parallelism of SSDs. The biggest reason SSDs are much faster than HDDs is due to the lack of moving parts, however this benefit created another issue: data transfer bottlenecks due to SSD using the much slower HDD infrastructure. This lead to the inception of NVMe, which is designed to allow SSDs to transfer data between the motherboard and the SSD at much higher rates. NVMe uses a process called command queuing to send requested data to the controller of the motherboard. Command queuing allows for NVMe to process more than 65,000 queues at one time, with each queue containing up to 65,000 commands.

SATA 2.5

SATA 2.5 refers to an HDD with 2.5 inch form factor where they are typically found in laptops, and the larger 3.5 inch HDDs are found in desktops.  The 2.5 inches refers to the size of the spinning platters inside the HDDs.  They are connected to the motherboard with a SATA cable internally.

3.5 inch form factor HDDs have capacities that can range from 500GB to 2TB, and in some cases as high as 8TB. SATA 2.5 inch form factor SSDs for laptops can have capacities that range from 500GB to 1TB, and in some cases as high as 3TB.


Magnetic Hard Disk Drives

A hard drive (HD) is an electro-magnetic data storage device that uses magnetic storage to store and retrieve digital data using one or more rigid rotating platters (aluminum or glass) coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. These platters are coated with a durable magnetic surface divided into sectors.  Each sector contains 512 bytes of storage, along with information about where the sector is located on the disk medium. Sectors are organized in concentric circles from the edge of the media inward toward the middle of the platter.  These concentric circles are called tracks. HDs are also the most important storage devices used by personal computers in which they store the operating system & loads it into the computer’s memory (RAM) at startup. HDs also store applications, system configuration files used by applications and the operating system, and data files created by the user.

Typical Hard Drive

Spin Rate

The speed at which hard disk media turns, its spin rate, is measured in revolutions per minute (rpm).

Hard Disk Spin Rate Comparison

Flash Drives

A flash drive is a small, ultra-portable storage device, which, unlike an optical drive or a traditional hard drive, it has no moving parts and it can retain its contents without electricity. Flash drives are often referred to as pen drives, thumb drives, or jump drives, but it can also be referred to as memory cards that are used for digital cameras, camcorders, and other types of digital media players.

Common Flash Memory Card Types

Flash Card Reader

A memory card reader is a device for accessing the data on a memory card such as a CompactFlash (CF), Secure Digital (SD), MultiMediaCard (MMC), microSD card, miniSD card, & xD card. Most card readers assign a separate drive letter to each slot on a PC. Memory card readers can come as separate external devices, some printers & multifunction devices also include card readers, as well as some computers have slots built in for card readers.

Typical Flash Card Reader

Storage Device Configurations

A common reason for adding storage is to create a fault-tolerant set of drives that will protect data in case a drive fails.

RAID Types

RAID (Redundant Array of Inexpensive (or independent) Disks) is a data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both. The most common RAID levels include:

  • RAID Level 0 (RAID 0):  Also known as a “stripe set” or “striped volume” splits (“stripes”) data evenly across 2 or more disks, without parity information, redundancy, or fault tolerance. The drives are treated as a single drive, and the drives are used to simultaneously store different portions of the same file. Striping boosts performance, but if either drive fails, all data is lost.  Don’t use striping for data drives.
  • RAID Level 1 (RAID 1):  Consists of an exact copy (or mirror) of a set of data on 2 or more disks and changes to the contents of one drive are immediately reflected on the other drive(s). This configuration offers no parity, striping, or spanning of disk space across multiple disks, since the data is mirrored on all disks belonging to the array, and the array can only be as big as the smallest member disk. This layout is useful when read performance or reliability is more important than write performance or the resulting data storage capacity. The array will continue to operate so long as at least one member drive is operational.
  • RAID Level 5 (RAID 5):  Consists of block-level striping with distributed parity. Three or more drives are treated as a logical array, and parity information (used to recover data in the event of a drive failure) is spread across all drives in the array.  Suitable for use with program and data drives.
  • RAID Level 1+0 (RAID 10):  Four drives combine striping plus mirroring for extra speed plus better reliability.  Suitable for use with program and data drives.  RAID 10 is a striped set of mirrors.
RAID 1+0 (RAID 10)

Most PCs with RAID support include support for Levels 0, 1, and 10. Some high-performance desktop systems also support RAID 5.  Systems that lack the desired level of RAID support can use a RAID add-on card.

Hot-Swappable Drives

Hot-swappable drives are drives that can be removed safely from a system or be connected to a system without having to shut the system down first.  The following drives can be hot swapped in Windows:

  • USB drives
  • eSATA drives
  • SATA drives
  • Flash memory drives

In most enterprise systems, the RAID drivers are hot swappable.