Storage is a process through which digital data is saved within a data storage device by means of computing technology. Storage is a mechanism that enables a. Storage devices are one of the core components of any computing device. They store virtually all the data and applications on a computer, except hardware. Data storage is a general term for archiving data in electromagnetic or other forms for use by a computer or device. Different types of data storage play different.
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A bit, or a group of malfunctioning physical bits not always the specific defective bit is known; group definition depends on specific storage device is typically automatically fenced-out, taken out of use by the device, and replaced with another functioning equivalent group in the device, where the corrected bit values are restored if possible.
The cyclic redundancy check CRC method is typically used in communications and storage for error detection. A detected error is then retried. Data compression methods allow in many cases such as a database to represent a string of bits by a shorter bit string "compress" and reconstruct the original string "decompress" when needed. This utilizes substantially less storage tens of percents for many types of data at the cost of more computation compress and decompress when needed. Analysis of trade-off between storage cost saving and costs of related computations and possible delays in data availability is done before deciding whether to keep certain data compressed or not.
For security reasons certain types of data e. 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.
In contemporary usage, "memory" is usually semiconductor storage read-write random-access memory , typically DRAM dynamic RAM or other forms of fast but temporary storage. Historically, memory has been called core memory , main memory , real storage or internal memory.
Primary storage also known as main memory or internal memory , often referred to simply as memory , is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required.
Any data actively operated on is also stored there in uniform manner. Historically, early computers used delay lines , Williams tubes , or rotating magnetic drums as primary storage.
By , those unreliable methods were mostly replaced by magnetic core memory. Core memory remained dominant until the s, when advances in integrated circuit technology allowed semiconductor memory to become economically competitive. This led to modern random-access memory RAM. It is small-sized, light, but quite expensive at the same time. The particular types of RAM used for primary storage are also volatile , i. As shown in the diagram, traditionally there are two more sub-layers of the primary storage, besides main large-capacity RAM:.
Main memory is directly or indirectly connected to the central processing unit via a memory bus. It is actually two buses not on the diagram: The CPU firstly sends a number through an address bus, a number called memory address , that indicates the desired location of data. Then it reads or writes the data in the memory cells using the data bus. Additionally, a memory management unit MMU is a small device between CPU and RAM recalculating the actual memory address, for example to provide an abstraction of virtual memory or other tasks.
As the RAM types used for primary storage are volatile uninitialized at start up , a computer containing only such storage would not have a source to read instructions from, in order to start the computer. Hence, non-volatile primary storage containing a small startup program BIOS is used to bootstrap the computer, that is, to read a larger program from non-volatile secondary storage to RAM and start to execute it.
A non-volatile technology used for this purpose is called ROM, for read-only memory the terminology may be somewhat confusing as most ROM types are also capable of random access. Many types of "ROM" are not literally read only , as updates to them are possible; however it is slow and memory must be erased in large portions before it can be re-written.
Some embedded systems run programs directly from ROM or similar , because such programs are rarely changed. Standard computers do not store non-rudimentary programs in ROM, and rather, use large capacities of secondary storage, which is non-volatile as well, and not as costly. Recently, primary storage and secondary storage in some uses refer to what was historically called, respectively, secondary storage and tertiary storage. Secondary storage also known as external memory or auxiliary storage , differs from primary storage in that it is not directly accessible by the CPU.
Secondary storage does not lose the data when the device is powered down—it is non-volatile. Per unit, it is typically also two orders of magnitude less expensive than primary storage. Modern computer systems typically have two orders of magnitude more secondary storage than primary storage and data are kept for a longer time there. In modern computers, hard disk drives are usually used as secondary storage. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds.
By contrast, the time taken to access a given byte of information stored in random-access memory is measured in billionths of a second, or nanoseconds. This illustrates the significant access-time difference which distinguishes solid-state memory from rotating magnetic storage devices: To reduce the seek time and rotational latency, data are transferred to and from disks in large contiguous blocks. When data reside on disk, accessing them in large blocks to hide latency offers an opportunity to design efficient external memory algorithms.
Sequential or block access on disks is orders of magnitude faster than random access, and many sophisticated paradigms have been developed to design efficient algorithms based upon sequential and block access. Some other examples of secondary storage technologies are flash memory e.
The secondary storage is often formatted according to a file system format, which provides the abstraction necessary to organize data into files and directories , providing also additional information called metadata describing the owner of a certain file, the access time, the access permissions, and other information. Most computer operating systems use the concept of virtual memory , allowing utilization of more primary storage capacity than is physically available in the system.
As the primary memory fills up, the system moves the least-used chunks pages to secondary storage devices to a swap file or page file , retrieving them later when they are needed. As more of these retrievals from slower secondary storage are necessary, the more the overall system performance is degraded. Tertiary storage or tertiary memory  provides a third level of storage.
Typically, it involves a robotic mechanism which will mount insert and dismount removable mass storage media into a storage device according to the system's demands; such data are often copied to secondary storage before use. It is primarily used for archiving rarely accessed information since it is much slower than secondary storage e. This is primarily useful for extraordinarily large data stores, accessed without human operators. Typical examples include tape libraries and optical jukeboxes.
When a computer needs to read information from the tertiary storage, it will first consult a catalog database to determine which tape or disc contains the information. Next, the computer will instruct a robotic arm to fetch the medium and place it in a drive. When the computer has finished reading the information, the robotic arm will return the medium to its place in the library.
Tertiary storage is also known as nearline storage because it is "near to online". The formal distinction between online, nearline, and offline storage is: For example, always-on spinning hard disk drives are online storage, while spinning drives that spin down automatically, such as in massive arrays of idle disks MAID , are nearline storage. Removable media such as tape cartridges that can be automatically loaded, as in tape libraries , are nearline storage, while tape cartridges that must be manually loaded are offline storage.
Off-line storage is a computer data storage on a medium or a device that is not under the control of a processing unit. Are the items you wish to store sensitive to cold, heat, moisture or dust? If you are storing valuable items such as documents, furs, electronics, computer equipment, stereos or television sets you may want to opt for a climate-controlled unit.
Many storage facilities also offer dust-free storage for your sensitive electronics. Will want to switch out the storage contents seasonally?
Often you will want to store your summer wardrobe or seasonal household items such as swimming pool equipment or patio furniture during the winter months. Space may vary for these items and perhaps even the need for climate or dust control. Make sure that you consider all your possible needs before renting your unit.
Do you need 24 hour tenant access? Be aware that not all facilities will allow you access to the unit during any given time of the day or night. Rules vary from one facility to the next.
While some units are accessible 24 hours a day, other facilities have limited hours of operation that limit access to your belongings. Check the rules before signing a contract if round-the-clock access is important to you. Do you need to store large items such as cars, campers or other motorized vehicles? Self storage can be a great option for storing vehicles. If needed, you can rent a climate-controlled unit to help preserve these items. You will want to be sure that you rent from a company with an established reputation.
Safety is another factor to consider. You will rest easier knowing that your valuables are properly secured. Learn the difference between your device and iCloud storage, ways to manage your space, and where to buy more if you run out.
The music you buy, the apps you download, the photos you take, and all of the other content that you enjoy on your device uses its storage.
And depending on the size of your capacity and how much content you have, your device can fill up and run out of storage. But you can free up space. Tap an app's name for more information about its storage. Or you can remove content from your apps—like photos, music, and Podcasts—or delete the apps that you're not using.
When you set up iCloud , you automatically get 5GB of free storage.
Computer data storage
This definition explains the meaning of data storage, also known as enterprise storage or storage, and the methods and technologies applied to capture. Storage at the edge is an expression that refers to data storage and backup routines used in portable and mobile computing. The term applies especially to. Computer storage is measured in bytes, kilobytes (KB), megabytes (MB), gigabytes (GB) and increasingly terabytes (TB). One byte is one.