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Standard Disk Interconnect
The Standard Disk Interconnect (SDI, sometimes Standard Disk Interface) was used by Digital Equipment Corporation for its line of RAxx disks, for example the RA90. There were two bi-directional serial communications paths between the controller and the drive. One path was for messages (from the controller to the drive) and responses (from the drive to the controller); messages controlled seeking, setting drive parameters, reporting errors, etc. This path was also used to transmit data to and from the drive. The other path consisted of a continuously transmitted set of control (controller-to-drive) or status (drive-to-controller) bits. There were about 6 bits in each direction, and they served the same purpose as having six dedicated lines in each direction. By encoding control signals serially they could be AC-coupled (with a transformer) to prevent ground loop problems and EMI issues between the controller and the drives, which could be connected by long cables, even to differen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until forced to resign in 1992, after the company had gone into precipitous decline. The company produced many different product lines over its history. It is best known for the work in the minicomputer market starting in the mid-1960s. The company produced a series of machines known as the PDP line, with the PDP-8 and PDP-11 being among the most successful minis in history. Their success was only surpassed by another DEC product, the late-1970s VAX "supermini" systems that were designed to replace the PDP-11. Although a number of competitors had successfully competed with Digital through the 1970s, the VAX cemented the company's place as a leading vendor in the computer space. As microcomputers improved in the late 1980s, especially wit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
External Memory Interface
An external memory interface is a bus protocol for communication from an integrated circuit, such as a microprocessor, to an external memory device located on a circuit board. The memory is referred to as external because it is not contained within the internal circuitry of the integrated circuit and thus is externally located on the circuit board. The external memory interface enables the processor to interface with third level caches, peripherals, and external memory. Some common external memory interfaces include: * DDR * DDR2 * GDDR Graphics DDR SDRAM (GDDR SDRAM) is a type of synchronous dynamic random-access memory (SDRAM) specifically designed for applications requiring high bandwidth, e.g. graphics processing units (GPUs). GDDR SDRAM is distinct from the more widely kn ... References {{reflist Computer memory ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disk Sector
In computer disk storage, a sector is a subdivision of a track on a magnetic disk or optical disc. Each sector stores a fixed amount of user-accessible data, traditionally 512 bytes for hard disk drives (HDDs) and 2048 bytes for CD-ROMs and DVD-ROMs. Newer HDDs use 4096-byte (4 KiB) sectors, which are known as the Advanced Format (AF). The sector is the minimum storage unit of a hard drive. Most disk partitioning schemes are designed to have files occupy an integral number of sectors regardless of the file's actual size. Files that do not fill a whole sector will have the remainder of their last sector filled with zeroes. In practice, operating systems typically operate on blocks of data, which may span multiple sectors. Geometrically, the word sector means a portion of a disk between a center, two radii and a corresponding arc (see Figure 1, item B), which is shaped like a slice of a pie. Thus, the ''disk sector'' (Figure 1, item C) refers to the intersection of a ''t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disk Read-and-write Head
A disk read-and-write head is the small part of a disk drive which moves above the disk platter and transforms the platter's magnetic field into electrical current (reads the disk) or, vice versa, transforms electrical current into magnetic field (writes the disk). The heads have gone through a number of changes over the years. In a hard drive, the heads ''fly'' above the disk surface with clearance of as little as 3 nanometres. The flying height has been decreasing with each new generation of technology to enable higher areal density. The flying height of the head is controlled by the design of an air bearing etched onto the disk-facing surface of the ''slider''. The role of the air bearing is to maintain the flying height constant as the head moves over the surface of the disk. The air bearings are carefully designed to maintain the same height across the entire platter, despite differing speeds depending on the head distance from the center of the platter. If the head h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mass Storage Control Protocol
The Mass Storage Control Protocol (MSCP) is a protocol that was designed by Digital Equipment Corporation of Maynard, Massachusetts for the purposes of controlling their high-end mass storage options. First implemented in the HSC50 hierarchical storage controller, the protocol quickly spread throughout the entire line of mass storage controllers built by DEC. The UDA50 is an implementation of MSCP built on a Unibus card; other implementations (for example, the RQDX) stretch down to the Q-bus and small, 5 megabyte disk drives and even diskettes. Designed to minimize the amount of CPU involvement, the protocol depends upon two queues. Into one queue are placed packets which fully describe the commands to be executed by the mass storage subsystem. To initiate an I/O request, the CPU has only to create a small data structure in memory, append it to a "send" queue, and if that is the first packet in the send queue, wake the MSCP controller. After the command has been executed, an app ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unibus
The Unibus was the earliest of several computer bus and backplane designs used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation (DEC) of Maynard, Massachusetts. The Unibus was developed around 1969 by Gordon Bell and student Harold McFarland while at Carnegie Mellon University. The name refers to the unified nature of the bus; Unibus was used both as a system bus allowing the central processing unit to communicate with main memory, as well as a peripheral bus, allowing peripherals to send and receive data. Unifying these formerly separate busses allowed external devices to easily perform direct memory access (DMA) and made the construction of device drivers easier as control and data exchange was all handled through memory-mapped I/O. Unibus was physically large, which led to the introduction of Q-bus, which multiplexed some signals to reduce pin count. Higher performance PDP systems used Fastbus, essentially two Unibusses in one. The syst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid-state Drive
A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is also sometimes called a semiconductor storage device, a solid-state device or a solid-state disk, even though SSDs lack the physical spinning disks and movable read–write heads used in hard disk drives (HDDs) and floppy disks. SSD also has rich internal parallelism for data processing. In comparison to hard disk drives and similar electromechanical media which use moving parts, SSDs are typically more resistant to physical shock, run silently, and have higher input/output rates and lower latency. SSDs store data in semiconductor cells. cells can contain between 1 and 4 bits of data. SSD storage devices vary in their properties according to the number of bits stored in each cell, with single-bit cells ("Single Level Cells" or "SLC ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tape Drive
A tape drive is a data storage device that reads and writes data on a magnetic tape. Magnetic tape data storage is typically used for offline, archival data storage. Tape media generally has a favorable unit cost and a long archival stability. A tape drive provides sequential access storage, unlike a hard disk drive, which provides direct access storage. A disk drive can move to any position on the disk in a few milliseconds, but a tape drive must physically wind tape between reels to read any one particular piece of data. As a result, tape drives have very large average access times. However, tape drives can stream data very quickly off a tape when the required position has been reached. For example, Linear Tape-Open (LTO) supports continuous data transfer rates of up to 360 MB/s, a rate comparable to hard disk drives. Design Magnetic tape drives with capacities of less than one megabyte were first used for data storage on mainframe computers in the 1950s. , capaci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ground Loop (electricity)
In an electrical system, a ground loop or earth loop occurs when two points of a circuit are intended to have the same ground reference potential but instead have a different potential between them. This is typically caused when enough current is flowing in the connection between the two ground points to produce a voltage drop and cause two points to be at different potentials. Current may be produced in a circular ground connection (ground loop) by electromagnetic induction. Ground loops are a major cause of noise, hum, and interference in audio, video, and computer systems. Wiring practices that protect against ground loops include ensuring that all vulnerable signal circuits are referenced to one point as ground. The use of differential signaling can provide rejection of ground-induced interference. Removal of safety ground connections to equipment in an effort to eliminate ground loops also eliminates the protection the safety ground connection is intended to provide. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RA90
The RA90 disk drive was the first Digital Equipment Corporation drive to be based on "thin film" technology. Prior to the RA90 all Digital disk drives used "oxide" disks, which were an aluminum disk coated with a polyurethane binder resin containing gamma ferric oxide particles as the recording medium. The 1988-released RA90, which held 1.2GB, was used with controllers implementing the Mass Storage Control Protocol. Overview The RA90 disk drive, in addition to being DEC's first step into ''thin film'' technology, also introduced another first for ''DEC''": ''Storage Arrays''. Their first was the ''SA600 Storage Array'', which had 4 or 8 drives. Other models were the SA550 and SA650 ''Mixed Storage Array''s, combining RA70s with RA82s (SA550) or RA90s (SA650). The SA482 used just RA82s instead of RA90s. Replacing the 1.2GB RA90s with 1.5GB RA92s, an ''SA800 Storage Array'' held 12GB. History The technology was pioneered by Ampex Corporation in Redwood City, California based on a s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Capacitive Coupling
Capacitive coupling is the transfer of energy within an electrical network or between distant networks by means of displacement current between circuit(s) nodes, induced by the electric field. This coupling can have an intentional or accidental effect. In its simplest implementation, capacitive coupling is achieved by placing a capacitor between two nodes. Where analysis of many points in a circuit is carried out, the capacitance at each point and between points can be described in a matrix form. Use in analog circuits In analog circuits, a coupling capacitor is used to connect two circuits such that only the AC signal from the first circuit can pass through to the next while DC is blocked. This technique helps to isolate the DC bias settings of the two coupled circuits. Capacitive coupling is also known as ''AC coupling'' and the capacitor used for the purpose is also known as a ''DC-blocking capacitor''. A coupling capacitor's ability to prevent a DC load from interfe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signal
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' includes audio, video, speech, image, sonar, and radar as examples of signal. A signal may also be defined as observable change in a quantity over space or time (a time series), even if it does not carry information. In nature, signals can be actions done by an organism to alert other organisms, ranging from the release of plant chemicals to warn nearby plants of a predator, to sounds or motions made by animals to alert other animals of food. Signaling occurs in all organisms even at cellular levels, with cell signaling. Signaling theory, in evolutionary biology, proposes that a substantial driver for evolution is the ability of animals to communicate with each other by developing ways of signaling. In human engineering, signals are typi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
