Data Storage Systems Information
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Data storage systems are used to store, protect and manage computer data. There are many different types of products. Examples include hard drives, tape drives, floppy drives, and removable cartridge drives. Hard drives (hard disks, fixed disk drives) are located inside the computer case and use either integrated drive electronics (IDE) or small computer system interface (SCSI) circuitry. Tape drives are used to copy data from a computer onto tape cartridges. External tape drives are more expensive than internal data storage systems, but can be used with more than one computer. Floppy drives store data on 3.5 in. floppy disks. Removable cartridges have a metal or plastic housing and can be inserted and removed like floppy disks. Although removable cartridge drives are relatively fast, their speeds are usually slower than those of fixed hard disks.
Data storage systems include optical storage devices such as compact-disc (CD) drives and digital versatile disk (DVD) drives. There are three main CD drive technologies: CD-ROM, CD-R and CD-RW. Compact disk, read-only memory (CD-ROM) drives can read, but not record data. Compact disk, recordable (CD-R) drives are write-once, read-many (WORM) devices that can record data one time and retrieve data multiple times. Compact disk, rewritable (CD-RW) drives can both write and erase data multiple times. The digital versatile disk (DVD) specification supports disks with capacities ranging from 4.7 GB to 17 GB and access rates between 600 Kbps and 1.3 Mbps. Most DVD drives are backwards-compatible with older CD-ROM drives and can play different types of CDs.
Specifications for data storage systems include width, height and length; capacity; internal and external transfer rate; and mounting style. Width, height and length are measured in English units such as inches (in) or metric units such as centimeters (cm) or millimeters (mm). Capacity is the amount of available space for data storage. Transfer rate is the speed at which bits of data are sent. The internal transfer rate is the speed at which bits of data are read from the disk and sent to the drive’s controller. The external transfer rate is the speed of the data exchange between the controller and the central processing unit (CPU). In terms of mounting styles, some data storage systems attach to a chassis or panel. Others are rack-mounted or free standing. Integrally mounted drives are soldered or hard-wired in place.
There are many different interfaces for data storage systems. Fibre Channel allows 2 Gbps data transfers and maps several common transport protocols to merge high-speed input/output (I/O) capabilities with network functionality. FireWire® is a cross-platform implementation of the high-speed serial data bus defined in IEEE 1394, a standard from the Institute of Electrical and Electronic Engineers (IEEE). FireWire is a registered trademark of Apple Computer, Inc. Universal serial bus (UBS) is the serial bus standard for low-to-medium speed peripheral device connections between PCs and peripherals. Data storage systems that use IDE and SCSI interfaces are also available.
Data storage systems may be manufactured, tested, and used based upon guidelines laid out in various standards. In addition to standards specific to data storage systems, guidelines for the use of general information technology equipment often cover use of these products as well. Example standards include:
IEC 60950-23 (IT equipment safety - large data storage equipment)
ISO 16963 (Test method for the estimation of lifetime of optical media for data storage)
ADA 1021 (Data integrity, redundancy, storage and accessibility)