Storage Devices: Magnetic Storage Devices, Optical storage Devices, Flash Memory
Magnetic Storage Devices
The most common type of storage device is magnetic storage device. In magnetic storage devices, data is stored on a magnetized medium. Magnetic storage use different patterns of magnetization to in a magnetizable medium to store data.
There are primarily 3 types of Magnetic Storage Devices as follows,
- Disk Drives:
Magnetic storage devices primarily made of disks are Disk Drives. Hard Disk Drive is a Disk Drive. HDD contains one or more disks that runs in a very high speed and coated with magnetizable medium. Each disk in a HDD comes with a READ/WRITE head that reads and write data from and onto the disk.
- Diskette Drives:
Diskette drives or floppy disks are removable disk drives. The discs in Hard Disk Drives are not meant to be removed, but in case of Floppy disks, the disks are removable from the drive which is called Floppy Disk Drive or FDD. Floppy disks comes with very little storage capacity and meant to be used as portable storage to transfer data from one machine to another. The FDD reads and writes data from and to the floppy disk. The floppy disk itself is covered with plastic and fabric to remove dust. Floppy disk does not contain any read and write head, the FDD contains the head.
- Magnetic Tape:
Magnetic tapes are those reels of tapes which are coated with magnetizable elements to hold and server written on it in one of the many magnetizing data storage pattern. Tape drives come with very high capacity of storage and still in use though personal computers, server etc. uses hard disk drives or other modern type of storage mechanism, tape drives are still in use for archiving hundreds of terabytes of data.
Operating Storage Types
Optical storage refers to recording data using light. Typically, that’s done using a drive that can contain a removable disk and a system based on lasers that can read or write to the disk. If you’ve ever used a DVD player to watch a movie, put a CD in a player to listen to music or used similar disks in your desktop or laptop computer, you’ve used optical storage.
Compared to other types of storage such as magnetic hard drives, the disks used in optical storage can be quite inexpensive and lightweight, making them easy to ship and transport. They also have the advantage of being removable, unlike disks in typical hard drive, and they’re able to store much more information than previous types of removable media such as floppy disks.
Among the most familiar types of optical storage devices are the CD, DVD and Blu-ray disc drives commonly found in computers. Initially, many of these drives were read-only, meaning they could only access data on already created disks and couldn’t write new content to existing or blank disks. Still, the read-only devices called CD-ROM drives revolutionized home and business computing in the 1990s, making it possible to distribute multimedia material like graphically rich games, encyclopedias and video material that anyone could access on a computer. Now, most drives can both read and write the types of optical disks they are compatible with.
Disks are available that can be written once, usually marked with the letter “R” as in “DVD-R,” or that can be written multiple times, usually marked with the letters “RW.” Similar drives are also found in most modern home video game consoles in order to read game software. Drives in computers and gaming systems can typically play movies and music on optical disks as well. Make sure you buy disks that are compatible with your drives and players.
Standalone players for audio CDs and TV-compatible players for Blu-ray discs are also widely available. Drives and players for older formats like HD-DVD and LaserDisc are still available as well, although they can be more difficult to find.
Flash memory (Known as Flash Storage) is a type of non-volatile storage memory that can be written or programmed in units called “Sector” or a “Block.” Flash Memory is EEPROM (Electronically Erasable Programmable Read-Only Memory) means that it can retain its contents when the power supply removed, but whose contents can be quickly erased and rewritten at the byte level by applying a short pulse of higher voltage. This is called flash erasure, hence the name. Flash memory is currently both too expensive and too slow to serve as main memory.
Flash memory (sometimes called “Flash RAM”) is a distinct EEPROM that can read block-wise. Typically the sizes of the block can be from hundreds to thousands of bits. Flash Storage block can be divided into at least two logical sub-blocks.
Flash memory mostly used in consumer storage devices, and for networking technology. It commonly found in mobile phones, USB flash drives, tablet computers, and embedded controllers.
Flash memory is often used to hold control code such as the basic input/output system (BIOS) in a personal computer. When BIOS needs to be changed (rewritten), the flash memory can be written to in block (rather than byte) sizes, making it easy to update. On the other hand, flash memory is not usedas random access memory (RAM) because RAM needs to be addressable at the byte (not the block) level.
Flash memories are based on Floating-Gate Transistors. Floating gate transistors are used in memory to store a bit of information. Flash memories are used in the device to store a large number of songs, images, files, software, andvideo for an extended period,etc.
History Flash Memory
In 1980’s Flash memory as invented by Fujio Masuoka, while working in Toshiba. In 1988, Intel introduced NOR flash memory chip having random access to memory location. These NOR chips were a well-suited replacement for older ROM chips. In 1989, with more improvement, NAND flash memory was introduced by Toshiba. NAND flash memory is similar to a Hard disk with more data storage capacity. After that, there has been a rapid growth in flash memory over the years passes.
Flash memory is an electronic chip that retains its stored data without any power. Flash memory is different from RAM.RAM is volatile memory, needs electricity and power to maintain its content. However, flash memory does notrequire the power for holding data. Flash memory was used in many devices like in form SD card, Pen-drive (moveable storage), camera card and video card, and so forth. Flash memory gives faster access to data content ascompared to hard disk. In hard-disk, disk rotation takes time to move on the particularcylinder, track orsector.However,in a flash, no rotating time dischas created abarrier for fast access.
Types of Flash Memory
Flash memory is available in two kinds NAND Flash and NOR Flash Memory. NAND and NOR flash memory both have different architecture and used for specific purpose.
NAND Flash Memory
In today is an environment where all devices require high data density, faster speed access and cost-effective chip for data storage. NAND memory has needed less chip area hence more data density. NAND Memory used the concept of the block to access and erases the data. Each block contains thedifferent size of pages various from bytes. MMU (Memory Management Unit) helps NAND to the first page the content or copied into RAM and then executed.
NOR Flash Memory
In the circuit of flash memory, memory cells are connected in parallel. It provides random or sequentially access memory. Data Reading process for NOR and RAM are similar. We can execute the code directly from NOR without copying into RAM. NOR memory ideal for runs small code instructions program. It referred to Code-storage applications. It used for low-density applications.
NOR flash provides support to bad block management. Bad block in memory is handled by controller devices to improve functionality.
We can use the combination of both NOR and NAND memory. NOR (software ROM) used for instruction execution,and NAND used for non-volatile data storage.
Limitation of Flash Memory
Although Flash memory gives many advantages, yet it has some flaw.
1) We can quickly read or programmed a byte at a time, but we cannot erase a byte or word. It can delete data in blocks at a time.
2) Bit flipping: Bit Flipping problem is more occur in NAND memory as compare to NOR. In Bit Flipping, a bit get reversed and create errors. For checking and correcting the bit error (EDC/ECC) detection and error correction code are implemented.
3) Bad block: Bad block are the blocks which can’t be used for storage. If scanning system gets fails to check and recognize badblock in memory. Then reliability of system gets reduced.
4) Usage of NOR and NAND memory: NOR is easy to use. Just connect it and use it. However, NAND not used like that. NAND has I/O interface and requires adriver for performing any operation. Read operation from NOR do notneedany driver.