Secondary Storage

= Storage devices =

Introduction
A computer is a programmable machine that receives input, stores and manipulates data, and provides output in a useful format.

While a computer can, in theory, be made out of almost anything (see misconceptions section), and mechanical examples of computers have existed through much of recorded human history, the first electronic computers were developed in the mid-20th century (1940–1945). Originally, they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs). [1] Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space. [2] Simple computers are small enough to fit into mobile devices, and can be powered by a small battery. Personal computers in their various forms are icons of the Information Age and are what most people think of as "computers". However, the embedded computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robots

Computer data storage
1GB of SDRAM mounted in a personal computer. An example of primary storage. 40GB PATA hard disk drive (HDD); when connected to a computer it serves as secondary storage. 160 GB SDLT tape cartridge, an example of off-line storage. When used within a robotic tape library, it is classified as tertiary storage instead.

Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data used for computing for some interval of time. Computer data storage provides one of the core functions of the modern computer, that of information retention. It is one of the fundamental components of all modern computers, and coupled with a central processing unit (CPU, a processor), implements the basic computer model used since the 1940s. In contemporary usage, memory usually refers to a form of semiconductor storage known as random-access memory, typically DRAM (Dynamic-RAM) but memory can refer to other forms of fast but temporary storage. Similarly, storage today more commonly refers to storage devices and their media not directly accessible by the CPU (secondary or tertiary storage) — typically hard disk drives, optical disc drives, and other devices slower than RAM but more permanent.[1] Historically, memory has been called main memory, real storage or internal memory while storage devices have been referred to as secondary storage, external memory or auxiliary/peripheral storage. The contemporary distinctions are helpful, because they are also fundamental to the architecture of computers in general. The distinctions also reflect an important and significant technical difference between memory and mass storage devices, which has been blurred by the historical usage of the term storage. Nevertheless

Storage device
A storage device is a hardware device capable of storing information. There are two types of storage devices used in computers; a primary storage device such as computer RAM and a secondary storage device such as a computer hard disk drive. In the picture to the right, is an example of a Drobo external secondary storage devise

Purpose of storage
Many different forms of storage, based on various natural phenomena, have been invented. So far, no practical universal storage medium exists, and all forms of storage have some drawbacks. Therefore a computer system usually contains several kinds of storage, each with an individual purpose. A digital computer represents data using the binary numeral system. Text, numbers, pictures, audio, and nearly any other form of information can be converted into a string of bits, or binary digits, each of which has a value of 1 or 0. The most common unit of storage is the byte, equal to 8 bits. A piece of information can be handled by any computer whose storage space is large enough to accommodate the binary representation of the piece of information, or simply data. For example, using eight million bits, or about one megabyte, a typical computer could store a short novel. Traditionally the most important part of every computer is the central processing unit (CPU, or simply a processor), because it actually operates on data, performs any calculations, and controls all the other components. Without a significant amount of memory, a computer would merely be able to perform fixed operations and immediately output the result. It would have to be reconfigured to change its behavior. This is acceptable for devices such as desk calculators or simple digital signal processors. Von Neumann machines differ in that they have a memory in which they store their operating instructions and data. Such computers are more versatile in that they do not need to have their hardware reconfigured for each new program, but can simply be reprogrammed with new in-memory instructions; they also tend to be simpler to design, in that a relatively simple processor may keep state between successive computations to build up complex procedural results. Most modern computers are von Neumann machines. In practice, almost all computers use a variety of memory types, organized in a storage hierarchy around the CPU, as a trade-off between performance and cost. Generally, the lower a storage is in the hierarchy, the lesser its bandwidth and the greater its access latency is from the CPU. This traditional division of storage to primary, secondary, tertiary and off-line storage is also guided by cost per bit

Primary storage devices
Decades of intensive research into integrated circuits has produced classes of electronic devices with amazing performance. Consider a music player the size of a deck of cards that can store all the works of Beethoven—with enough room left over to store a set of encyclopedias. At the heart of this success story are two technologies: processors and storage. This article examines two key storage technologies in modern electronic devices: random access memory (RAM) and read only memory (ROM). Because they provide high-speed storage, they enable the performance we expect in modern computers. Memory chips are everywhere: in your car, television, and phone. They come in many different flavors, although they all perform essentially the same function—to store data and provide for its retrieval. The economic driver for the development of these chips has historically been the computer industry. However, as the price has plummeted, the consumer electronics industry has embraced them wholeheartedly. Two of the most successful gadgets in the last decade (the digital camera and the portable music player) are built around memory chips. Both types of memory are normally packaged as integrated circuits, which are small electronic circuits that consist mostly of semiconductors. These are referred to as microchips, ICs, memory chips, or chips. Beyond that point, the differences between the two systems begin to become important. Random access memory is examined in the next section, and then it is followed with a discussion of read only memory.

RAM(Random Access Memory)
The name random access memory is an artifact of hardware evolution. Random access means that the stored data can be accessed in any order, which is in contrast to the more restricted access provided by other memory systems, such as tape and disk drive. The access time to any piece of data stored on in RAM is essentially the same. RAM is normally used in computer systems for main memory or primary storage. This is where running programs and the data they use are stored. Moving data from primary storage to the processor requires only a few cycles, although retrieving data from a hard drive can take considerable longer. For this reason, modern operating systems run primarily in RAM, and as they load and run additional applications, they move these programs and their data into RAM for faster processing. RAM can be categorized as volatile or non-volatile. Volatile means that all data is lost when the chip is powered down. Historically, non-volatile RAM was a tiny part of the market, although consumer electronics have changed that situation. When referring to computer systems, most RAM remains volatile. Non-volatile RAM and its uses are discussed later in this essay

ROM(Read Only Memory)
Non-volatile memory retains data even when not powered. The two common types of non-volatile memory are read only memory and flash memory. There are several types of read only memory (ROM), although most are obsolete. These ROMs are called read only because they cannot be modified by the casual user (and some types cannot be modified at all). ROMs have traditionally been used in computer systems to store configuration data, such as bootstrap or BIOS code, which requires fast access. The first ROMs were mask-programmed ROMs, which had 1s and 0s actually burned into the integrated circuit. This technique was simple but inflexible, and it was often used to contain the startup code (bootstrap) for early microcomputers. Mask ROM is now obsolete. The Programmable Read Only Memory (PROM) was the next step. The PROM is a memory array consisting of a grid of fuses. Typically, the blank PROM comes with all bits set to 1. During programming, the fuses that represent the zero bits are blown by the programming device, which sends high voltage pulses to destroy individual fuses. The PROM is a cheaper and more flexible approach than mask ROM, although each PROM can still be programmed only once. PROMs are reliable, permanent, and relatively fast. They are still in limited use; however, they have largely been supplanted by erasable versions of ROM.

Secondary Storage
Secondary storage technology refers to storage devices and storage media that are not always directly accessible by a computer. This differs from primary storage technology, such as an internal hard drive, which is constantly available.

Examples of secondary storage devices include external hard drives, USB flash drives, and tape drives. These devices must be connected to a computer's external I/O ports in order to be accessed by the system. They may or may not require their own power supply.

Examples of secondary storage media include recordable CDs and DVDs, floppy disks, and removable disks, such as Zip disks and Jaz disks. Each one of these types of media must be inserted into the appropriate drive in order to be read by the computer. While floppy disks and removable disks are rarely used anymore, CDs and DVDs are still a popular way to save and transfer data.

Because secondary storage technology is not always accessible by a computer, it is commonly used for archival and backup purposes. If a computer stops functioning, a secondary storage device may be used to restore a recent backup to a new system. Therefore, if you use a secondary storage device to backup your data,

Also known as external memory and auxiliary storage, secondary storage is a storage medium that holds information until it is deleted or overwritten regardless if the computer has power. For example, a floppy disk drive and hard disk drive are both good examples of secondary storage devices. As can be seen by the below picture there are three different types of storage on a computer, although primary storage is accessed much faster than secondary storage because of the price and size limitations secondary storage is used with today's computers to store all your programs and your personal data. Finally, although off-line storage could be considered secondary storage, we've separated these into their own category because these types of media can be easily removed from the computer and stored elsewhere.

Different Storage Devices for Computers
Computers have the capability to store your information in a variety of different ways. All of these different ways require a specific storage device. More than likely, you have used a variety of different storage devices on your computer. You just may not have realized it at the time. Storage by way of zip drives and floppy discs is now a thing of the past. There are many new solutions for computer users to store large amounts of data.

Hard Drive (Internal)
You computer's hard drive is the first most important type of storage. Anything that you download, applications that you install, your pictures, videos and music are all stored directly to your hard drive. Basically, anything that is on your computer is stored to your internal hard drive. Internal hard drive capacity is measured in gigabytes. For example, you may have a 500GB SATA hard drive on your computer. Also, internal computer hard drives have different speeds such as 5400RPM and 7200RPM. This reading is the speed that the hard drive disk spins. A faster hard drive will have higher RPM. The faster the hard drive spins, the faster your hard drive can read data, as well as write data.

External Hard Drives
External hard drives are exactly the same as internal drives, with one exception. Rather then being enclosed inside your computer, external hard drives have their own separate casing and sit externally to your computer. External hard drives can connect to your computer in a variety of ways. Some common connection types are: USB 2.0, ESATA, Firewire 400 and Firewire 800. External hard drives measure capacity in gigabytes and have different speeds as well. For the most part, external hard drives are used for backup and storing files that a computer user may want to transport.

Network Attached Storage/NAS Server
Another common form of computer storage is network attached storage or NAS. Network attached storage is a method commonly used by businesses to share files between computers. A NAS is simply a storage device connected to a computer network. This is beneficial because many computers can read and write to a NAS. Network attached storage capacity is measured in gigabytes. Also, NASs are available with different hard drive speeds.

Many at home computer users often create their own NAS devices by connecting an external hard drive to their router. This allows them to access it wirelessly, as well as share it with other computers.

Optical Media Storage/Optical Drive
Optical media storage is basically writing data to a CD or DVD. When your burn a CD, you are storing songs and music on the CD so that you can listen to it later. If you are burning a DVD, you are storing a video on it so that you can watch it later. CD-RW and DVD-RW media has the capability to be recorded on and erased later if necessary. This makes optical media storage ideal for transporting relatively small amounts of data.

Flash Drives
Flash drives, or thumb drives, are one of the newest forms of computer storage. These drives connect to any computer by way of USB. Often times, students as well as business professionals, use flash drives as a simple way to transport text documents to and from work, and to and from school. When flash drives were first released, storage capacity was rather limited. However, companies are now manufacturing flash drives with huge storage capacities, up to 64GB.