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Dd (Unix)
dd is shell command for reading, writing and converting file data. Originally developed for Unix, it has been implemented on many other environments including Unix-like operating systems, Windows, Plan 9 and Inferno. The command can be used for many purposes. For relatively simple copying operations, it tends to be slower than domain-specific alternatives, but it excels at overwriting or truncating a file at any point or seeking in a file. The command supports reading and writing files, and if a driver is available to support file-like access, the command can access devices too. Such access is typically supported on Unix-based systems that provide file-like access to devices (such as storage) and special device files (such as /dev/zero and /dev/random). Therefore, the command can be used for tasks such as backing up the boot sector of a drive, and obtaining random data. The command can also support converting data while copying; including byte order swapping and conve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Ken Thompson
Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science. Thompson worked at Bell Labs for most of his career where he designed and implemented the original Unix operating system. He also invented the B (programming language), B programming language, the direct predecessor to the C (programming language), C language, and was one of the creators and early developers of the Plan 9 from Bell Labs, Plan 9 operating system. Since 2006, Thompson has worked at Google, where he co-developed the Go (programming language), Go language. A recipient of the Turing award, he is considered one of the greatest computer programmers of all time. Other notable contributions included his work on regular expressions and early computer text editors QED (text editor), QED and ed (text editor), ed, the definition of the UTF-8 encoding, and his work on computer chess that included the creation of endgame tablebases and the chess machine Belle (chess machine), Belle. He won ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Computer File
A computer file is a System resource, resource for recording Data (computing), data on a Computer data storage, computer storage device, primarily identified by its filename. Just as words can be written on paper, so too can data be written to a computer file. Files can be shared with and transferred between computers and Mobile device, mobile devices via removable media, Computer networks, networks, or the Internet. Different File format, types of computer files are designed for different purposes. A file may be designed to store a written message, a document, a spreadsheet, an Digital image, image, a Digital video, video, a computer program, program, or any wide variety of other kinds of data. Certain files can store multiple data types at once. By using computer programs, a person can open, read, change, save, and close a computer file. Computer files may be reopened, modified, and file copying, copied an arbitrary number of times. Files are typically organized in a file syst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Typographical Error
A typographical error (often shortened to typo), also called a misprint, is a mistake (such as a spelling or transposition error) made in the typing of printed or electronic material. Historically, this referred to mistakes in manual typesetting. Technically, the term includes errors due to mechanical failure or slips of the hand or finger, but excludes ''errors of ignorance'', such as spelling errors, or changing and misuse of words such as "than" and "then". Before the arrival of printing, the copyist's mistake or scribal error was the equivalent for manuscripts. Most typos involve simple duplication, omission, transposition, or substitution of a small number of characters. "Fat finger" typing (especially in the financial sector) is a slang term referring to an unwanted secondary action when typing. When a finger is bigger than the touch zone, with touchscreens or keyboards, there can be inaccuracy and one may hit two keys in a single keystroke. An example is '' buckled'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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EBCDIC
Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight- bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding six-bit binary-coded decimal code used with most of IBM's computer peripherals of the late 1950s and early 1960s. It is supported by various non-IBM platforms, such as Fujitsu-Siemens' BS2000/OSD, OS-IV, MSP, and MSP-EX, the SDS Sigma series, Unisys VS/9, Unisys MCP and ICL VME. History EBCDIC was devised in 1963 and 1964 by IBM and was announced with the release of the IBM System/360 line of mainframe computers. It is an eight-bit character encoding, developed separately from the seven-bit ASCII encoding scheme. It was created to extend the existing Binary-Coded Decimal (BCD) Interchange Code, or BCDIC, which itself was devised as an efficient means of encoding the two ''zone'' and ''number'' punches on punched cards into six ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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ASCII
ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control characters a total of 128 code points. The set of available punctuation had significant impact on the syntax of computer languages and text markup. ASCII hugely influenced the design of character sets used by modern computers; for example, the first 128 code points of Unicode are the same as ASCII. ASCII encodes each code-point as a value from 0 to 127 storable as a seven-bit integer. Ninety-five code-points are printable, including digits ''0'' to ''9'', lowercase letters ''a'' to ''z'', uppercase letters ''A'' to ''Z'', and commonly used punctuation symbols. For example, the letter is represented as 105 (decimal). Also, ASCII specifies 33 non-printing control codes which originated with ; most of which are now obsolete. The control cha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Byte Order
'' Jonathan_Swift.html" ;"title="Gulliver's Travels'' by Jonathan Swift">Gulliver's Travels'' by Jonathan Swift, the novel from which the term was coined In computing, endianness is the order in which bytes within a word (data type), word of digital data are transmitted over a data communication medium or Memory_address, addressed (by rising addresses) in computer memory, counting only byte significance compared to earliness. Endianness is primarily expressed as big-endian (BE) or little-endian (LE), terms introduced by Danny Cohen into computer science for data ordering in an Internet Experiment Note published in 1980. Also published at The adjective ''endian'' has its origin in the writings of 18th century Anglo-Irish writer Jonathan Swift. In the 1726 novel ''Gulliver's Travels'', he portrays the conflict between sects of Lilliputians divided into those breaking the shell of a boiled egg from the big end or from the little end. By analogy, a CPU may read a digital word b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Boot Sector
A boot sector is the disk sector, sector of a persistent data storage device (e.g., hard disk, floppy disk, optical disc, etc.) which contains machine code to be loaded into random-access memory (RAM) and then executed by a computer system's built-in firmware (e.g., the BIOS). Usually, the first sector of the hard disk is the boot sector, regardless of sector size (512 or 4096 bytes) and partitioning flavor (Master boot record, MBR or GUID Partition Table, GPT). The purpose of defining one particular sector as the ''boot sector'' is inter-operability between firmware and various operating systems. The purpose of chain-loading, first firmware (e.g., the BIOS), then code in the boot sector, and then, for example, an operating system, is maximal flexibility. The IBM PC and compatible computers On an IBM PC compatible machine, the BIOS selects a boot device, then copies the first sector from the device (which may be a master boot record, MBR, Volume Boot Record, VBR or any exec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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/dev/random
In Unix-like operating systems, and are special files that provide random numbers from a cryptographically secure pseudorandom number generator (CSPRNG). The CSPRNG is seeded with Entropy_(computing), entropy (a value that provides randomness) from environmental noise, collected from device drivers and other sources. Users can obtain random numbers from the CSPRNG simply by reading the file. Not all operating systems implement the same methods for and . In older operating systems, typically Blocking (computing), blocked if there was less Entropy (computing), entropy available than requested; more recently (see below for the differences between operating systems) it usually blocks at startup until sufficient entropy has been gathered, then unblocks permanently. The device typically was never a blocking device, even if the pseudorandom number generator seed was not fully initialized with entropy since boot. This special file originated in Linux in 1994. It was quickly adopted b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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/dev/zero
is a special file in Unix-like operating systems that provides as many null characters (ASCII NUL, 0x00) as are read from it. One of the typical uses is to provide a character stream for initializing data storage. Function Read operations from return as many null characters (0x00) as requested in the read operation. Unlike , may be used as a source, not only as a sink for data. All write operations to succeed with no other effects. However, is more commonly used for this purpose. When is memory-mapped, e.g., with mmap, to the virtual address space, it is equivalent to using anonymous memory; i.e. memory not connected to any file. History was introduced in 1988 by SunOS-4.0 in order to allow a mappable BSS segment for shared libraries using anonymous memory. HP-UX 8.x introduced the MAP_ANONYMOUS flag for mmap(), which maps anonymous memory directly without a need to open . Since the late 1990s, MAP_ANONYMOUS or MAP_ANON are supported by most UNIX versions, removing the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Device File
In Unix-like operating systems, a device file, device node, or special file is an interface to a device driver that appears in a file system as if it were an ordinary file. There are also special files in DOS, OS/2, and Windows. These special files allow an application program to interact with a device by using its device driver via standard input/output system calls. Using standard system calls simplifies many programming tasks, and leads to consistent user-space I/O mechanisms regardless of device features and functions. Overview Device files usually provide simple interfaces to standard devices (such as printers and serial ports), but can also be used to access specific unique resources on those devices, such as disk partitions. Additionally, device files are useful for accessing system resources that have no connection with any actual device, such as data sinks and random number generators. There are two general kinds of device files in Unix-like operating syst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Computer Data Storage
Computer data storage or digital data storage is a technology consisting of computer components and Data storage, recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processing unit (CPU) of a computer is what manipulates data by performing computations. In practice, almost all computers use a storage hierarchy, which puts fast but expensive and small storage options close to the CPU and slower but less expensive and larger options further away. Generally, the fast technologies are referred to as "memory", while slower persistent technologies are referred to as "storage". Even the first computer designs, Charles Babbage's Analytical Engine and Percy Ludgate's Analytical Machine, clearly distinguished between processing and memory (Babbage stored numbers as rotations of gears, while Ludgate stored numbers as displacements of rods in shuttles). This distinction was extended in the Von Neumann archite ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Device Driver
In the context of an operating system, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and other computer programs to access hardware functions without needing to know precise details about the hardware being used. A driver communicates with the device through the computer bus or communications subsystem to which the hardware connects. When a calling program invokes a routine in the driver, the driver issues commands to the device (drives it). Once the device sends data back to the driver, the driver may invoke routines in the original calling program. Drivers are hardware dependent and operating-system-specific. They usually provide the interrupt handling required for any necessary asynchronous time-dependent hardware interface. Purpose The main purpose of device drivers is to provide abstraction b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |