# Storage System

As the demand for technology and technology itself continues to excel throughout history, so does user's wants and needs. The user's lifestyle pertaining to computers may revolve around publishing documents, creating presentations, media management, networking on the internet, and much more. In correlation with their wants and needs, there's the need to be able to have access to storage of the data being produced. Storage is also referred to as 'memory', as it can be any type of hardware that's functionality includes, storing data, maintaining downloaded files along with extracting files as well. This can be performed through both permanent and temporary storage along with being internal to a device, or external.
As the spectrum of technology storage is a wide-range and continues to grow, benefits of storage included today are:
* Cost-efficient
* Speed
* Enhanced efficiency
Examples of storage includes:
* Hard Disk Drives / Solid State Drives
* Storage Area Networks
* Network Attached Storage
* Computer Disks
* USB
* Cloud Computing

## Storage Media, Storage Technology, and Volatility

Storage media is the hardware in which information is physically stored. This differs from the storage device which is usually the docking bay for the storage medium. One example of a storage device would be your CD/DVD drive in which you place your disks when inserting them into your computer or your USB flash drive reader. Storage media would be the actual CD/DVD disk itself or the memory within your computer known as RAM (Random Access Memory). Storage media can be internal or external meaning that it can be either hard-wired to the computer (ex. hard drive) or it can be a separate physical storage facility thats meant to be more mobile, (ex USB Flash Drive). Internal storage media is usually faster since it is hard-wired to the desktop or laptop and does not requires any extra space outside of the computer. On the other hand, external media is very mobile, can be transferred from one computer to another rather quickly, and is easily secured in a safe place separate from your main working station. On top of this the Non-Volatility of these storage medias have made them very valuable. Normally when a computer is shut down, any unsaved information is wiped clean from the RAM. Or if the information isn't being used, while the computer is still on, the RAM may delete it to make room for processes being recalled more frequently. Storage media on the other hand, saves data despite the computer being powered down and can only be deleted by the user. From this, storage media such as flash drives and data CD's are more commonly used for the user's wants and needs.
Storage Technology usually comes in three forms; magnetic, optic, and solid state. Some common magnetic storage systems are hard drives, floppy disks, and cassette tapes. Though cassette tapes don't work with computers, they use the same technology. This type of technology stores binary code using polar alignments on the magnetic medium and can change those alignments as needed when information is altered, deleted, or rewritten. The magnet does this by converting the binary code from 1's and 0's to positive and negative charges, respectively, which are recorded on an iron oxide film inside the media. Optics use laser beams which rely on marking the media. In this case, lasers burn in lines of data which represent the binary code it is converting. "Rewritable" media has also become a popular choice for those who want to reuse the same disk. Rewritable media relies on changing the reflectivity of the media instead of scarring it. When the binary number 1 is recognized, the laser alters the reflection of the discs surface in certain spots. Data is then separated by the pits in between reflectivity which represent the binary number 0 so that 1's alter the reflection and 0's leave the reflection of the media as is. This creates a "bouncing-wave" like appearance on the surface of the disk called an Amplified Spontaneous Emission or ASE for short. Solid State Drives, or SSD's as they are called, do not contain any moving parts such as lasers or magnetic heads. They operate electronically by storing the binary code as electrons which are either trapped or not trapped inside the flash memory cells within the unit. These types of media tend to be faster than the other two since they rely on electrical polarity within a cell instead of electronic motors to be read or rewritten. This also makes them more resistant to shock, allows them to run more quietly, and reduces the latency of the media. Typical storage media of this kind are "jump" drives or "thumb" drives, but some computers use this technology in their hardware as well.

## Clusters, Sectors, and Tracks

Hard disks have many circular pieces called platters inside them. These platters have two sides are made up of tracks, sectors, and clusters. A cluster is a group of sectors, and a sector divides tracks into pie shaped sections. Each cluster, sector, and track is numbered in order to help the computer quickly locate where specific stored data is. For example, data can be saved to side 2, sector 1, track 5. A track can be compared to the grooves on a music record, because there are physical indents where the data is actually stored. Data is read and written by a read/write head, also commonly referred to as a “head.” Each platter has a head. When data is to be stored on a hard disk, the heads will align with the same track on every platter, and write the data across each one. There are a few measurements you can take to see how well a hard disk preforms. The most important measurement is calculating seek time. Seek time will tell you how long it takes for a head to move from one track to another. The quicker the seek time the better because that would mean data can be reached faster.

## Random vs. Sequential

When thinking of storage systems, one could presume that all of your data in one folder is located next to each other within the hard drive. This is false when talking about random access. With random access your information can be pulled from any location on the disk. Meaning, your one folder could have its data scattered about the physical hard drive. The benefit of this type of storage is that you could access data in any order. Think of it as your CD player, your favorite song ends and you want to hear it again just hit back and you instantly hear it again. It’s fast and nearly instantaneous, unlike sequential. You could think of sequential access like a cassette within a cassette player. When a song finishes and you want to listen to it again, you must rewind the cassette, or if you want to skip a song you must fast forward the tape. This is used with magnetic tape drives which, are used for backup purposes. Even though in random access media devices may seem like data could be misplaced or somehow lost in the sea of data. When created, every file is given a unique name by the computer system, other wise called addressable media, in order to keep tabs on all the data.
Random access and sequential access of data are two separate ways a computer can access data. Random access is the ability to access data in any given location within the hard drive, quickly and efficiently. Most computers use random access today, because it saves the user time, as well as avoids confusion. Sequential access requires data being accessed in a sequence. Examples of sequential access would be: data on a disk file, or magnetic tape data storage. This can be useful to some users, if they are purposely attempting to process a sequence of data elements in order. However, this can also be time consuming for users who are trying to find a certain file on a disk or tape, which requires skimming through all of the data in a sequence. An example of a comparison between random access and sequential access would be the A-Z method. Sequential access would inquire the user to go through letters A-Z to achieve the goal of meeting point” Z”; whereas with random access, the user is able to jump directly to point “Z”.

## Storage Devices and Storage Media

The storage medium is a part of the storage system where the actual data is stored, such as on a DVD or a memory card. This medium can then be put into a storage device like a DVD player or phone to read this data. You usually find these two parts to be separate pieces, making the storage medium removable. Some storage devices can be found inside of the system unit, while others are plugged into an external port. There are letters on the storage device that go along with this that helps the unit to identify them. These letters or words describe where these are and what they are used for. For example, when you plug in a USB into the USB port on the computer, while viewing this USB in “My Computer” you will see a letter next to it verifying what it is used for in the system unit. Storage devices contain primary and secondary memory. Primary memory is volatile memory, which means that when the device is shut off, the information is lost. Secondary is the exact opposite, being non-volatile in that the memory remains even if the computer is turned off. The problem with these devices is you must be cautious with how they are treated, especially if they have important information. Misplacing or mistreating can result in a loss of important data that could be impossible to get back depending on the circumstances.

# Hard Drives

Every computer contains one, if not two, hard drives. There are internal and external hard drives. The internal hard drive is located inside the system unit, and the external hard drive is connected to the computer for extra storage. It is vital that an owner of a computer purchases an external hard drive to backup his or her computer in case it crashed. An external hard drive is extremely convenient to store information; however, one must be cautious of the possibility of "hard drive theft" because it is easy for someone to access a random, external hard drive into their own computer. Many people today use a finger print or password to access to their hard drive because of this reason. Without a hard drive, one could not store the countless amount of information contained to a computer. The hard drive holds a port to connect to the motherboard. There are a wide range of capacity for hard drives, depending on the computer owner's preference. Magnetic hard drives and solid-state hard drives are two common hard drives used for computers. A magnetic hard drive is the term computer users mean when they say hard drive, and solid-state hard drives cause flash memory technology. Without hard drives, many information and data would be lost and forgotten.
Hard drives are used as primary storage units to store most data and computer programs to operate on a computer. The two types of hard drives available for purchase are: internal hard drives, and external hard drives. There are many things to consider if you are a consumer seeking these storage devices. The internal hard drive, which can be included in the computer before purchase, is directly connected to the motherboard, (A.K.A the brain of the computer), as well as other components inside the tower or casing of the computer/laptop. An external hard drive is commonly used among users who are either portably transporting data/programs from device to device, or seeking extra storage space for their files. External hard drives can be very small, and convenient for traveling with data. There are multiple different options to explore while considering a hard drive: speed, consistency, and durability. The types of hard drives offered include either of the following: magnetic storage, optical storage, and electrons which use flash memory media.
* Magnetic hard drive
* Solid-state hard drive

## Hard drive interface standards

A hard drive interface (or hard disk interface) refers to "the logical and physical means by which the hard disk connects to the PC." For over a decade, the most common hard drive interface was by a wide margin AT Attachment/ATA, also known as Parallel ATA or PATA. ATA is still used in modern PCs, but it is not as significant as the more modern interface, Serial ATA, or SATA. The more modern SATA uses smaller cables, is more reliable, and possesses greater bandwidth than the now-obsolete PATA. SATA and ATA are not compatible, but there exist adapters to connect ATA interfaces with SATA drives (or SATA interfaces with ATA drives). Another common interface is SCSI (or Small Computer System Interface), which is especially useful for multitasking where multiple hard drives are used, such as in a workplace environment. Essentially, the difference between these three interfaces can be summarized as follows:
* ATA interfaces are cheaper and are still fairly common, but they are slower and outdated.
* SATA interfaces are the most useful: the only problem is that you need to buy additional adapters for them to interact with older systems, but they are still relatively cheap, they have high speed, and their wires are small, which frees up more room in the computer and helps prevent overheating.
* SCSI interfaces are very fast and can handle a wide range of applications and amount of data, but they are quite inexpensive and impractical for home use; SCSI is used more for networks than personal use.

## "The Cloud"

Cloud storage, also referred to as "The Cloud", is simply the use of a remote storage device that is accessed by means of the internet. Cloud storage has seen a massive increase in popularity over the last few years, and the industry for it has grown substantially to the point where there are now hundreds of companies that offer a variety of cloud storage services. More specifically, some cloud services focus only on digital pictures or email messages, while other systems store all kinds of digital data. Some services, like Google Drive, allow users to save their files in one of many massive data centers Google operates where, for instance, multiple users can collaborate on projects by having access to the same file.
As the cloud’s popularity is growing, more and more businesses are transferring over to its storage capabilities. Many businesses are using the application as a back up program for their software and documents. By scheduling a set time for the computer to automatically transfer documents over, businesses can be sure that their information lies safely in the hands of the Internet without having to spend the tedious amount of time and cost of backing it up manually. Though the different applications of the cloud do sometimes have a monthly fee to pay, it is a small price to pay for the time and convenience it lends you. By utilizing these applications, anybody is able to access their documents anywhere worldwide. An individual is no longer tied down to just one electronic device in one set area, but can instead revise a version of a document on their laptop and then pull it up at work for a presentation the next day. This is just one example of the hundreds of ways that the application can be used conveniently to meet your day-to-day needs. The cloud is connecting electronic devices all across the globe and making every day processes just a little bit easier.
Despite of the fact, that a Cloud storage term has appeared in use quite recently, people and businesses actuality use online storages for a long time. For example saving copies of letters on mail server or retrieving network configuration files from TFTP server. These days Cloud storage term should be considered is one of many other Cloud computing services. It could be provided as separate product – “Storage-as-a-Service”, and also be a part of others, for example: Infrastructure-as-a-service, Platform-as-a-service or Software-as-a-service. As was mentioned above, the rapidly growing popularity is primarily due to quite low cost for a service itself (Storage-as-a-Service) when users pay only for the volume of data they stored, and if we are talking about the Infrastructure or Platform services which are great opportunity for business to reduce an IT expenses as well. With all advantages are given by online storing, there are few things users should be aware deciding entrust the care of their data to the provider. It might be as purely technical concerns (reliable internet connectivity, provider’s backup algorithm, disaster recovery, security of access, etc.) and legal aspects as well (ownership of data, jurisdiction, rights to audit).

## Disk Access Time

Disk access time is a measurement that calculates the amount of time it takes before for a drive to read and write data. Disk access time involves three major steps: seek time, rotational delay (or rotational latency), data movement time. Seek time is the amount of time it takes for the head to move to the disk to prepare for reading. Rotational delay is the delay that occurs when waiting for the disk to begin rotating. Data movement time involves the movement of data from the disk to memory of the computer or the movement of data from the memory of the computer to the disk. Maximum rotational latency is the time it takes for the disk to perform a full rotation excluding any acceleration time. There are two types of ways in which a disk rotates: constant linear velocity and constant angular velocity. Constant linear velocity occurs when the rotational speed of the disk is dependent upon the location of the head. Constant angular velocity occurs when the disk is spun at the same speed regardless of the location of the head, like vinyl records. Certain low-noise disks utilize a slower disk access time to reduce noise created by the hard drive. Slower rotational speeds and seek speeds are purposefully installed to make sure that audible clicks and crunching sounds don’t interfere with recordings.

# Flash Memory
### Flash Memory and How It Works

Flash memory is a type of storage device that uses electronic memory. Flash memory comes in a variety of ways and is known as a solid state storage device, meaning “there are not moving parts – everything is electronic instead of mechanical.” Flash memory is used in many different devices, such as, computers, digital cameras, and mobile phones. Flash memory is a type of EEPROM chip. EEPROM stands for Electronically Erasable Programmable Read Only Memory. Inside of a flash memory chip is a grid of columns and rows with a cell. There are two transistors at each intersection and a thin oxide layer separates them. One transistor is known as a floating gate and the other one is known as the control gate. An electrical charge comes through the columns to the floating gate, which is called tunneling. The electrical charge causes the floating gate transistor to act like an electron gun. When the electrons get trapped on the other side of the thin oxide layer, closer to the control gate transistor, they act like a barrier between the two transistors. A cell sensor monitors the level of the charge. If the flow is above the 50% threshold, it has a value of 1 and if it is less, the value changes to 0. This is how information/data is being read on the flash memory device. Nowadays, flash memory has become the “dominant memory type wherever a system requires a significant amount of non-volatile, solid state storage.”

### Embedded Memory

Embedded memory is becoming an increasingly popular type of flash memory due to its small, convenient size. In today's society these types of memory can be found in phones, cameras, gaming devices, and even handheld devices like a GPS. In July 2013, Samsung announced that they developed the world's fastest embedded memory. These new products will be available in the 16, 32, and 64 GB sizes and feature an interface speed of 400 MB/s. This will increase user's abilities to multitask and perform tasks such as file transferring, browsing, and gaming. It also decreases the amount of time it takes to boot and load applications. This is a key factor in mobile devices where the physical space for additional storage or memory is limited. Memory cards are being used less and less when manufacturing mobile devices and smartphones. One limitation of the chip is the amount of memory it could store. The larger the chip, the more expensive the device is going to cost. Something else to consider is the problem that arises if the device breaks. Any valuable information that was stored on it is virtually irretrievable. That is one advantage of having a removable memory as discussed below.

### Flash Memory Cards and Readers

If you want a fast and easy method of storing various types of media, you can't get much better than a flash memory card. Most modern portable devices contain a flash memory card because of its versatility and ease of use; cellphones, mp3 players, and digital cameras are but just a few examples of products that benefit from flash memory cards. However, just like how not all electronic devices can use the same type of battery, not all flash memory cards are compatible with every electronic portable device. That's why it's always important to read your user manual for instructions on the right card to purchase if you ever need a replacement.
Although the devices themselves can only use a specific flash memory card model, most modern desktop and notebook computers come with a flash memory card reader. The reader typically supports a number of different cards so you're able to organize and transfer the data from card to computer. If you aren't one of the fortunate few to have this reader built in to your computer, external models are sold at most stores that sell computer components and they're inexpensive.
Although a general-purpose flash memory card is used for most applications, there are other special memory cards that are made only for one unique purpose. For example, a professional compact flash memory card is designed for professional photographers for improved speed, quality, and storage capacities, taking telling a story through a picture to the next level. Also, special gaming flash memory cards are used for all game consoles, like Nintendo Wii and Sony PlayStation, to hold saved game data. Other special flash memory cards include HD memory cards for capturing high-definition videos; netbook memory cards to expand the storage of a netbook computer; and Wi-Fi enabled flash memory cards used to wirelessly upload photos from a camera.

### USB Flash Drives

The USB storage device is one that has been growing rapidly in popularity. It is a very user friendly form of storage. To save information to a USB flash drive, one simply must plug in the USB drive into the USB port (usually on the side or back of the computer), click the "save as" option on their project, then select the drive on their computer which represents the USB. Then one can eject the USB and take the saved information anywhere they need. USBs are quickly advancing as well. There are now ways that you can create an entire mobile computer, a fingerprint enabled secure file, and secure the use of your computer all with the use of a single USB flash drive. These new advances are sure to be hot on the market. USBs are high in demand right now, not just because of their technical abilities but also because of how you can choose a USB to fit into any lifestyle or match any personality. There are thousands of custom USBs available in stores and online. These range in colors, sizes, amounts of memory, and even shapes. USB flash drives are something that will definitely be here to stay for a while longer, even with the ever emerging cloud. USB flash drives are also very secure ways to store information. Since they are not connected to the Internet, they cannot be hacked, and some can be encrypted to prevent unauthorized access. The one down side to this use is the possibility of the flash drive being lost or stolen, but with proper precautions and organization, this can be avoided. Flash drives also preserve data and documents in a non-volatile state. As some specialized computers (such as theatre control boards) are prone to crashes and glitches, saving information on a flash drives prevents is from being corrupted or lost in the event of a system crash or other glitch. In simpler systems, flash drives can be used as the central storage point for a computer. While this may be inefficient on most machines, those that are single use and do not require large amounts of memory can benefit from this, as the system is flexible, and more memory space can be added as needed. However, the primary benefit of flash drives remains the mobility. Flash drives are an inexpensive and more secure alternative to the cloud and other means of Internet storage.
USB drives are the perfect devices for transporting data and files. They are easy to use and their portability makes them incredibly convenient. In addition to storing files, they can also be used to run portable apps. Certain applications can be turned into portable versions of themselves. You can have access to various software applications to use on any computer. Free programs exist to convert applications to portable ones to, in essence, create a portable PC on a thumb drive. USB drives range in storage capacity from 2 GB to 4 TB. With 4 TB of storage in such a portable size, the limits to their use are virtually endless.
USB drives can be password protected, or some can even be secured using biometric features, like a finger print. There are some concern related to USB drive security. They can contain large amounts of information, and given their portability, they can be used for transporting files secretly. Anyone with access can simply plug a USB drive into a computer, copy files onto it, and remove them from the premises. USB drives carry an additional security risk in that they can contain malware that can be automatically launched using AutoPlay (which can be disabled) as soon as they are plugged in.

### Solid State Drives

SSDs serve the same purpose as HDDs: they store data and files for long-term use. The difference is that SSDs use a type of memory called “flash memory,” which is similar to RAM—but unlike RAM, which clears its data whenever the computer powers down, the data on an SSD persists even when it loses power. SSDs use a grid of electrical cells to quickly send and receive data. These grids are separated into sections called “pages,” and these pages are where data is stored. Pages are clumped together to form “blocks.” SSDs are called “solid-state” because they have no moving parts. SSD's are much faster than traditional hard disks (especially during random reads/writes) as they do not rely on mechanics to locate data (which becomes slow when data is located at different ends of a hard drive).
However, as with flash memory, SSD's can last only a finite amount of writes. As an SSD is used, the electrical charges within each of its data cells must be periodically reset. Unfortunately, the electrical resistance of each cell increases slightly with every reset, which increases the voltage necessary to write into that cell. Eventually, the required voltage becomes so high that the particular cell becomes impossible to write to. While SSD's include extra capacity (which cannot be seen by the user) solely to replace cells which become damaged this way, after a lot of writes (usually over 150 TB), the drive will fail. However the volumes of writes (reading alone isn't affected) required to do so is far out of the reach for most users.
The main drawback of a SSD as compared to a HDD is price; SSD's cost significantly more than a HDD, but the price difference is rapidly falling, and more and more computers now include a SSD by default.

## Remote Storage

Remote storage is there to expand the disk space without hard disks and isn’t connected to the computer directly but accessed through internet. That way you can access your files wherever you are, whenever you want, on your laptop or Smartphone or even a different computer. This is the basic concept of cloud storage. When you need to access a file, you open the file as usual but if the data isn’t on your local volume, Remote Storage retrieves the information from a media library. When data is removed from a file, the logical size of the file remains but the physical size is reduced.
Being much faster and reliable than storage devices like CDs, DVDs, hard disks, and flash drives, an online remote storage provides protection against system errors like viruses, and enables one to recover lost data from any potential system crashes. Being critical to not only businesses, but home computer users as well, an online storage provides low-cost and easily accessible security for data management and storage. To assure maximum security, many online companies automatically backup systems on a daily, weekly, or monthly basis, to an “electronic vault.” Also, unlike CDs or DVDs, using remote storage diminishes its vulnerability to damage and data loss. Living in today’s high-tech society, the online remote storage system is definitely a very essential, yet affordable tool to assure that the countless amounts of data being saved on devices is still remediable after a computer failure.

## Floppy Disk

The floppy disk drive was invented at IBM by Alan Shugart in 1967. The first floppy drives used an 8-inch disk that was later called a "diskette" as it got smaller, which evolved into the 5.25-inch disk that was used on the first IBM Personal Computer in August 1981. The 5.25-inch disks were dubbed "floppy" because the diskette packaging was a very flexible plastic envelope, unlike the rigid case used to hold today's 3.5-inch diskettes.
The floppy disk is an archaic physical external storage device that is now obsolete. There might be some banks that still use this storage medium, but any business or person who is considered computer literate does not use this system to store information. The down sides to floppy disks are that they are not compatible with any device that is contemporary, their security is non-existent, and the storage capacity is low - usually with a maximum of 1.44MB. The last version of a floppy disk was released in 1987 by IBM.

## Holographic Storage

Holographic storage utilizes photo-sensitive media and innovative laser beam technology as a means of computer storage. This new storage method has the ability to store 1,000 DVD's into this 4 square inch storage device. This is unlike previous methods of data recording, such as magnetic and optical hard drives, which involve a rotating disk or simple 2D lasers. Instead, holographic storage begins with a single laser that is split into two separate parts -- the signal beam (carries data), and the reference beam (reconstructs hologram when prompted). A spatial light modulator is used to encode data for the signal beam, followed by a conversion of electronic data into binary code. It is then arranged into a specific pattern of dark and light pixels (representing zeros and ones), consisting of >1 million bits each. The signal and reference beams intersect, and a holographic image is created through a 3D refraction that is etched into the media. Advantages include a safe, fast, reliable, and portable system of storage. Disadvantages include expense, limited capacity, and recording fails. UV rays can also erase the data, which makes this method unstable in the long-term. Since the concept is still in its infancy, however, problems are expected to diminish greatly over time.

## Storage area network

Storage area networks are clusters of high performance computers used to transfer huge amounts of data. SANs are also used for distributed processing applications requiring fast local network performance and designed specifically for data management. SANs move storage resources off the common user network and into an independent network. What this does is allow each server too access any shared storage extremely quickly, as if it was already attached to the server. Typically, a SAN is assembled using three components: cabling, host bus adaptors, and switches.
What makes a good storage area network? A SAN definitely needs to be indestructible and have a built-in protection against any potential harmful failure. If a SAN is vulnerable to failures and is unable to recover lost data, an enterprise may even go out of business! Secondly, a vast amount of storage capacity is another essential to a valuable storage network; since the number of devices connected to one host system may increase by time, the organization’s storage and processing also needs to expand accordingly. A big advantage of using a good storage area network is the fact that even if all of one’s system servers crash, the SAN remains online and provides disaster recovery.

## Network Attached Storage

NAS is a type of dedicated file storage device typically connected by a wired networking connection, therefore only providing local area network users with storage. NAS supports file transfers, in which it will back up any data that appears in the form of files, such as email boxes, web content, remote system backups. The main advantage of a network attached storage is that network storage is no longer limited to the amount the computing device can hold. NAS devices typically look very box-like, without a keyboard or display. NAS products come in levels of capable storage space, drive capacity and drive scalability, often placed into one of 3 categories: Desktop NAS, devices aimed at small businesses and home users; Mid-market NAS, devices capable of running several hundred terabytes but not clustering; Enterprise NAS, devices that can store huge amounts of files, including virtual images, and being able to NAS cluster.

## NAS vs SAN

Both systems of storage serve different purposes for their clients. The main difference between SAN storage and NAS storage is the way that the systems interact with the network. A NAS network will behave in a way that makes it similar to any other network component. In contrast, the storage devices of a SAN network are found in a separate network but connected to the main one. Overall though, both systems are used for storage and over time the performance offered by both is becoming harder to distinguish. For example a SAN uses Fibre Channel interconnects while NAS makes Ethernet and TCP/IP connects, but now many SAN systems are switching over to those connection routes NAS systems use.

# Optical Discs
## Characteristics

An optical disc is a flat, circular disc that stores data and is made out of a very strong plastic called polycarbonate substrate. This helps to protect the disc with many layers of coating. Data on these discs are read optically, which means that they store data using laser beams. Data can be stored on one or both sides of the disc. The track, which is a single spiral around the disc, spins from inside the center track (or groove) to the outermost track for the data to be read. Most people today have already switched from VHS movies to DVD movies, and now to Blu-ray DVDs. The advancement in technology has made viewing and burning capabilities for DVDs and CDs much more beneficial. These optical discs do not degrade, like VHS and magnetic media do. Optical discs are used in our every day lives for storage, backing up, photos, movies, music, and much more.
Read only discs are molded and stamped to show the data so that it can only be read (and not over written). This happens with most CDs for music and software, and DVDs for movies. A recordable or rewritable optical disc with a CD or DVD uses a laser to represent the data. An example of this would be burning a CD for music, or an iMovie project to a DVD. There is a complex process that takes place when writing the data on the optical disc. To mold or stamp the discs, bumps (called pits) are formed on the disc’s surface. The places that are not changed on the optical discs are called lands. Switching from a pit to a land represents a 1 (like discussed in the system unit). CD discs use infrared lasers, DVDs use red lasers, and Blu-ray discs use blue-violet lasers. These different types of lasers are used to store different amounts of data at a more compact size.
Optical drives are the machines that read the discs of CDs, DVDs, and BD drives. Many households have switched to Blu-ray DVD players. However, users are upset because only BD discs can be played on BD drives which is considered a hassle to some. These drives are also used to burn data on the discs.

## History

Optical disks were invented in 1958 by David Paul Gregg, he patented them. James T. Russell was then the first person to have made a recording audio digitally to an optical disk. Later Sony and Phillips research physicists made the CD’s we know today that can store large amounts of data. For this first generation of CD’s they could hold up to 75 minutes of audio with 650Mb of storage. The purpose of the first generation was only for audio and computer software. They were capable of making a CD video but the VHS cassette was more popular at the time and it cost too much to produce them. These CD’s were read with an infrared laser. Later the second generation could store even more data and was used for video. They were read with a visible laser light which allowed the lands a pits to be smaller thus creating more space to for more data. They allowed 4.7 GB of storage on a standard single disc. The third generations are being developed to create even more storage available, like a Blu-ray disc. The Blu-ray disc use blue-violet lasers. There is even a fourth generation to be discovered that could hold up to one terabyte of storage.

## CDs, DVDs, and BDs

Read-only optical discs include CD-ROM, DVD-ROM, and BD-ROM discs. These are CDs or DVDs that come with something already prerecorded on them and they cannot be cleared. This is because the pits that are molded into the surface of the disc are permanent. There are also read-only discs for video games and different software.
Recordable optical discs are also sometimes referred to as write-once discs. This means that these can be written to but the discs cannot be reused or erased. These include CD-R, DVD-R, DVD+R, and BD-R discs. The difference between the DVD-R and the DVD+R is the standard being used. There is also a DVD-R DL and a DVD+R DL, which indicates whether or not it is dual layer. Using DVD+R will allow you to instantly eject the DVD without having to wait for the finalized version. It also allows you to record some of the DVD on a personal computer and some of it on the TV. Another feature is that is it 100% compatible with all DVD players. Recordable CDs are often used for backing up files, making music CDs, or sending large files to other people. BD-R discs are used for even larger back ups that need even more storage and they are used for high-definition multimedia files.
Rewritable optical discs include CD-RW, DVD-RW, DVD+RW, and BD-RE discs. These can be written on and then erased and rewritten on. To rewrite on these types of discs they use phase change technology. So basically the rewriteable disc is coated with a metal alloy compound. They then use heating and cooling to write on the disc without making it permanent. These are used for backing up files but they are more convenient than recordable optical discs because they can be used multiple times.

### Details about CDs

Compact Disc (CD) is used to store video, audio, and data in different formats classified in the Rainbow Books. It includes formats like CD-ROM (Compact Disc Read-Only Memory), CD-R (Compact Disc- Recordable), CD-RW (Compact Disc-ReWritable), VCD (Video Compact Disc), photo CD, and Enhanced Music CD. Compact Disc comes in standard 12 cm (120mm) or 8 cm (80mm) in diameter. The most popular is the 12 cm type with a 74- or 80-minute audio capacity and a 650 or 700 MB (737,280,000 bytes) data capacity. The 8 cm type is used in electronic devices like portable compressed digital audio players or data storage products like miniature CD recorders. CD-Rs were invented by Philips and Sony and together with CD-ROM there were about 30 billion CDs sold worldwide in 2004. The high-capacity recordable CDs can hold 90 or 99 min of audio on a 12 cm disc and 30 minutes of audio on a smaller disc (8 cm). The ability to write beyond the manufacturer’s declared capacity on a CD-R or CD-RW disc is called oversizing or overburning. However, Overburning might affect product warranties and result in lost data so it is not recommended. However, it might affect product warranties and result in lost data so it is not recommended. These days, more and more compact discs are being replaced by flash drives or downloading.

### Details about BDs

The newest form of optical disk is the Blu-ray disk (BD), which was officially announced on February 19, 2002, and was first available to consumers on April 10, 2003. Blu-ray gets its name from the blue laser that reads it (as opposed to the red laser that reads DVDs). BDs have more storage capability than its predecessor and also has a variety of new functions that DVDs did not have, such as the following: record high-definition television without losing quality, record one program while watching another at the same time, automatically search for an empty space on the disc to avoid recording over a program, and access the Web to download subtitles and other features. The way BDs achieve this is by having smaller pits, so more data can be stored, and having a laser with a shorter wavelength, a blue laser, that can read more precisely. DVDs could not fit more information because a red laser is not precise enough to read pits that are packed together as close as the pits on a BD. Pits on a DVD could be a minimum of 0.4 microns, while BDs pit minimum is 0.15 microns. Also, the track pitch on BDs has been reduced from 0.74 microns to 0.32 microns. Because of all these improvements, a BD can hold more than 25 GB of information, which is five times the amount that a DVD can hold.

##### How to Repair a Scratched CD or DVD

Compact Discs (CDs) and Digital Video Discs (DVDs) both store their data externally on a disk. Unfortunately, as we all have experienced, these disks often times get scratched, making the CD or DVD skip, or sometimes not work at all. Depending on where the scratch is located, the disc may or may not be able to be repaired. It seems scratches on the top, shiny part of the disc are harder to repair than if the scratch is on the lower plastic part of the disc. Although some companies are developing scratch resistant discs, their efforts may be in vain due to technology moving fast past these forms of storage. For those people still utilizing CDs and DVDs, scratches on them can be annoying and frustrating. There are a few simple remedies consumers can try to repair their discs and attempt to get more life out of them. The first step is to clean the disc with a mild soap and water. This can help by removing any finger prints that may be hindering the disks’ functionality. Users then want to dry the disc with lint free cloth, as even the smallest fibers can scratch and damage the disc further. After the disc is dry, the user can then apply toothpaste to it, smoothing it out in a straight direction from the disc’s center. After this, the disc should be rewashed to remove any excess paste. If this procedure is successful, the toothpaste will fill in the scratches so the disc can again be played with little or no skipping. Often times, scratches to these discs are too severe for this method to help. If that is the case, companies advise consumers to discard the disc altogether. Luckily, as technology continues to advance, the reliance on these forms of storage is decreasing, and with it, the annoyance and frustration that comes from their malfunctioning.

##### Are Optical Discs Becoming Obsolete?

While Optical Discs may be excellent media of storage, their necessity has now come into question with the ever advancing of technology. Floppy disks used to be what everyone used to store information and that soon became obsolete. As the cycle of technology inevitably catches up to optical discs, they may no longer be as useful as before. First, there’s the rise of technologies that no longer make use of optical discs because of the size. Most tablets and laptops no longer having optical drives because they take up space and may make the device less portable. Next is the fact that there are many more storage options that have become available that are much more convenient. Cloud storage has been on the rise as well as regular flash drives have had an increase in storage capacity as compared to optical discs. Then there’s the fact that many media companies have moved to a disc free environment. Streaming services have made renting CDs and DVDs obsolete. Gamers no longer buy physical discs but rather just download a digital copy. Even music has moved to a streaming service that makes buying physical albums and LPs more of a novelty. Finally, there is the fact that consumers want what’s convenient and optical discs are no longer as convenient as they used to be. However which way you look at it, the advancement of technology will eventually make anything obsolete. The future holds many possibilities for other forms of storage and that too will eventually become obsolete.

## Smart Cards

A smart card is a credit card-sized piece of plastic that contains computer circuitry, like a processor, memory, and storage. Smart cards can only store low amounts of data, around 8 kilobytes of RAM or 346 kilobytes of ROM. The processor is actually a microprocessor, and it is situated under a gold contact pad on one side of the card. The processor in the card has the capability to encrypt the data so that only authorized access is allowed. The purpose of a smart card is to store sensitive data securely, usually identification or digital cash. Unlike a credit card where all of the information on it can be read easily and identity theft is more common, the smart card cannot be physically read and it puts up a difficult fight against a hacker trying to access the data. To make it even more secure, some smart cards actually store biometric data to even further ensure that only the correct user can use it. A smart card is used by sliding it through, placing it in, or placing it in front of a smart card reader. This allows for the smart card reader to interact with the smart card by transferring the data on the card. An example of this is having a smart card reader on a locked door. The authorized user, a government official, places their smart card in front of the smart card reader on the door and the data on the card would be read by the reader. Once the reader acknowledges that the government official is allowed in, the reader would unlock the door and the official could walk in. All in all, the smart card is a great new technology that is making transactions and equipment safer.

## Large Computer Storage Systems

Major companies and organizations require large computer systems that can store their massive amounts of data. The amount of data that the world needs to store is growing at a phenomenal rate, predicted to increase by half in 2014 alone. Regulations have been put in place by the government to make companies keep data and information about clients and customers. This information is stored in the same types of hardware that everyday consumers would use but on a much larger scale. Many hard drives are connected and used together to increase the amount of data that can be saved. A leader in the industry, IBM, is currently at work on the largest storage server ever with an incredible 120 petabytes of space. This server is going to be comprised of over 200,000 standard hard drives connected in a large warehouse. Some companies may also use a system called RAID, or redundant arrays of independent disks. This method uses two or more hard drives which contain redundant copies of the same data in order to process and access it faster. This can be done one of two ways. The first method, disk striping, actually separates and spreads the files out over multiple hard drives while the second method, disk mirroring, has an exact duplicate of the information on the first.

# Review

* Read Computer Data Storage

## Review Questions

* True or False; A magnetic hard drive uses flash memory.
* True or False; A Blu-ray disc offers a larger storage capacity than a DVD disc.
* True or False; Folders are places on a storage medium that hold files.
* True or False; Holographic storage uses lasers to produce three dimensional representations of data.
* True or False; NAS and SAN technologies refer to the same type of storage setup.
* A _____ is anything that is stored on a storage medium.
* A _____ _____ _____ is a type of flash memory device that is inserted into a USB port.
* Music and software typically use a _____ disc.
* Most computers use a _____ _____ as the primary storage system.
* A drive that uses optical discs is known as an _____ _____.

### Answers

* False
* True
* True
* True
* False
* file
* USB flash drive
* CD
* hard drive
* optical drive

## Glossary

* BD-R a Blu-ray disc that is recordable
* BD-RE a Blu-ray disc that is rewritable
* BD (Blu-Ray disc) a disc with a high storage capacity of approximately 25 or 50 GB. Commonly used in HD movies
* CD a disc with a low storage capacity of approximately 650 MB. Commonly used in music and software
* CD-R a CD disc that is recordable
* CD-ROM a CD that can only be read from but not able to write over
* CD-RW a CD that is rewritable
* cluster a sector that is the smallest addressable area of a disk
* cylinder a collection of hard drive tracks
* disk access time how long it takes to locate and read data from some storage medium
* disk cache memory that improves the time it takes to read from or write to a hard disk
* DVD a disc with a medium storage capacity of approximately 4.7 GB or 8.5 GB. Commonly used in software, movies and games
* DVD-R/DVD+R a DVD that is recordable
* DVD-ROM a DVD that can only be read from but not able to write over
* DVD-RW/DVD+RW a DVD that is rewritable
* embedded flash memory flash memory chips used in products
* file anything stored on a storage medium
* filename the name given to the file
* flash memory nonvolatile memory that can be found in a computer or used in a storage medium
* flash memory card a flash memory medium often found in digital cameras and other small devices
* folder a named place on a storage medium where files are kept
* hard drive a storage system found in most computers
* holographic storage a medium that stores data in three dimensions using multiple blue laser beams
* hybrid hard drive a hard drive with both flash memory and magnetic components
* magnetic hard drive a hard drive with one or more metal magnetic disks, an access mechanism and read/write heads
* magnetic tape storage media that stores data as a series of magnetic spots
* network attached storage (NAS) a high-performance storage device individually connected to a network to provide storage for computers on that network
* online storage remote storage devices accessed via the internet (i.e. cloud storage)
* optical disc a storage medium that reads and writes using a laser beam
* optical drive a drive used with optical discs (e.g. CD, DVD, BR)
* RAID (redundant arrays of independent disks) the configuration of several hard drives working together to improve performance and/or reliability
* remote storage a storage device that not directly connected to the computer that uses it (e.g. cloud storage)
* sector a small piece of a track
* smart card a small card-sized circuit piece that can store data
* solid-state drive (SSD) a hard drive that uses flash memory (rather than metal magnetic hard disks)
* storage area network a network of hard drives or other devices that provide storage for a computer network
* storage device hardware in which a storage medium is inserted to be read from or written to
* storage medium the part of a storage system where the data is stored (e.g. CD)
* track a circular path on the surface of a disk where data is recorded
* USB flash drive a storage device, that uses flash memory, that is inserted in a USB port

# References

* ↑ https://www.inkling.com/read/dummies-comptia-aplus-clarke-tetz-3rd/chapter-5/understanding-hard-drive
* ↑ http://kb.sandisk.com/app/answers/detail/a_id/8150/~/difference-between-sequential-and-random-access-operations
* ↑ http://www.dineshbakshi.com/igcse-gcse-ict/storage-devices-and-media>
* ↑ http://www.computerhope.com/jargon/h/harddriv.htm
* ↑ http://it.med.miami.edu/x929.xml
* ↑ http://www.pcmag.com/article2/0,2817,2404258,00.asp
* ↑ https://www.ifixit.com/Wiki/Hard_Drive_Interfaces
* ↑ http://www.newegg.com/product/CategoryIntelligenceArticle.aspx?articleId=209
* ↑ http://www.adrc.com/interfaces.html
* ↑ http://computer.howstuffworks.com/cloud-computing/cloud-storage1.htm
* ↑ http://www.theguardian.com/media-network/media-network-blog/2013/jun/19/how-businesses-using-cloud
* ↑ http://www.thesecurityadvocate.com/2013/03/20/cloud-service-contracts-breaking-down-the-all-important-service-level-agreement-sla/
* ↑ http://computer.howstuffworks.com/flash-memory1.htm
* ↑ http://smithsonianchips.si.edu/ice/cd/MEMORY97/SEC11.PDF
* ↑ http://www.pcmag.com/article2/0,2817,2388408,00.asp
* ↑ http://www.newegg.com/product/CategoryIntelligenceArticle.aspx?articleId=220
* ↑ http://www.usbgeek.com/search?q=USB&search-button.x=0&search-button.y=0
* ↑ http://www.howtogeek.com/203061/don%E2%80%99t-panic-but-all-usb-devices-have-a-massive-security-problem
* ↑ https://www.makeuseof.com/tag/solidstate-drives-work-makeuseof-explains/
* ↑ https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2003/cc759742(v=ws.10)
* ↑ http://www.spamlaws.com/online-remote-storage.html
* ↑ https://computer.howstuffworks.com/floppy-disk-drive1.htm
* ↑ http://www.vibrant.com/blog/holographic-storage-101.html
* ↑ http://searchstorage.techtarget.com/definition/storage-area-network-SAN
* ↑ http://compnetworking.about.com/od/networkstorage/g/storage_san.htm
* ↑ http://www.snia.org/education/storage_networking_primer/san/what_san
* ↑ http://compnetworking.about.com/od/itinformationtechnology/l/aa070101a.htm
* ↑ http://searchstorage.techtarget.com/definition/network-attached-storage
* ↑ http://compnetworking.about.com/od/networkstorage/f/san-vs-nas.htm
* ↑ http://www.thefreedictionary.com/compact+disc+read-only+memory
* ↑ http://netforbeginners.about.com/cs/multimedia/a/DVD_explained_3.htm
* ↑ http://www.osta.org/technology/cdqa7.htm
* ↑ http://www.osta.org/technology/cdqa7.htm
* ↑ http://electronics.howstuffworks.com/blu-ray1.htm
* ↑ http://electronics.howstuffworks.com/how-to-fix-scratched-dvd.htm
* ↑ http://compreviews.about.com/od/cddvd/a/Death-of-PC-Optical-Drives.htm
* ↑ http://computer.howstuffworks.com/question332.htm
* ↑ http://phys.org/news/2011-08-petabytes-ibm-largest-storage-array.html
* Wikipedia Computer Data Storage