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Magic SysRq Key
The magic SysRq key is a key combination understood by the Linux kernel, which allows the user to perform various low-level commands regardless of the system's state. It is often used to recover from freezes, or to reboot a computer without corrupting the filesystem. Its effect is similar to the computer's hardware reset button (or power switch) but with many more options and much more control. This key combination provides access to powerful features for software development and disaster recovery. In this sense, it can be considered a form of escape sequence. Principal among the offered commands are means to forcibly unmount file systems, kill processes, recover keyboard state, and write unwritten data to disk. With respect to these tasks, this feature serves as a tool of last resort. The magic SysRq key cannot work under certain conditions, such as a kernel panic or a hardware failure preventing the kernel from running properly. Commands The key combination consists o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Colemak
Colemak is a keyboard layout for Latin-script alphabets, designed to make typing more efficient and comfortable by placing the most frequently used letters of the English language on the home row. Created on 1 January 2006, it is named after its inventor, Shai Coleman. Most major modern operating systems such as Mac OS, Linux, Android (operating system), Android, ChromeOS, and Berkeley Software Distribution, BSD support Colemak natively. A program to install the layout is available for Microsoft Windows. On Android and iOS, the layout is offered by several virtual keyboard apps like GBoard and SwiftKey, as well as by many apps which support physical keyboards directly. __NOTOC__ Overview The Colemak layout was designed with the QWERTY layout as a base, changing the positions of 17 keys while retaining the QWERTY positions of most non-alphabetic characters and many popular keyboard shortcuts, supposedly making it easier to learn than Dvorak Simplified Keyboard, Dvorak layout for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PowerPC
PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., Apple–IBM–Motorola alliance, known as AIM alliance, AIM. PowerPC, as an evolving instruction set, has been named Power ISA since 2006, while the old name lives on as a trademark for some implementations of Power Architecture–based processors. PowerPC was the cornerstone of AIM's PReP and Common Hardware Reference Platform (CHRP) initiatives in the 1990s. Originally intended for personal computers, the architecture is well known for being used by Apple's Power Macintosh, PowerBook, iMac, iBook, eMac, Mac Mini, and Xserve lines from 1994 until 2005, when Mac transition to Intel processors, Apple migrated to Intel's x86. It has since become a niche in personal computers, but remains popular for embedded system, embedded and high-performanc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File System Permissions
Most file systems include attributes of files and directories that control the ability of users to read, change, navigate, and execute the contents of the file system. In some cases, menu options or functions may be made visible or hidden depending on a user's permission level; this kind of user interface is referred to as permission-driven. Two types of permissions are widely available: traditional Unix file system permissions and access-control lists (ACLs) which are capable of more specific control. File system variations The original File Allocation Table file system has a per-file all-user read-only attribute. NTFS implemented in Microsoft Windows NT and its derivatives, use ACLs to provide a complex set of permissions. OpenVMS uses a permission scheme similar to that of Unix. There are four categories (system, owner, group, and world) and four types of access permissions (Read, Write, Execute and Delete). The categories are not mutually disjoint: World includes Group, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SVGALib
SVGAlib was an open-source low-level graphics library which ran on Linux and FreeBSD and allowed programs to change video mode and display full-screen graphics, without the use of a windowing system. Some popular games like '' Quake'' and ''Doom'' have been ported to use SVGAlib. History The first version of SVGALib was based on version 1.2 of another library, VGALib. SVGALib was popular in the mid-1990s. Toward 2000, many applications that used it migrated to X11 The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting wi ... and SDL, which could (until SDL 2.0) make use of SVGAlib as a video driver. References External links SVGAlib*Development versions(link on the site itself is broken) Articles with example C code Free computer libraries Graphics libraries {{Free-software ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Real-time Computing
Real-time computing (RTC) is the computer science term for hardware and software systems subject to a "real-time constraint", for example from event to system response. Real-time programs must guarantee response within specified time constraints, often referred to as "deadlines". Ben-Ari, Mordechai; "Principles of Concurrent and Distributed Programming", ch. 16, Prentice Hall, 1990, , p. 164 The term "real-time" is also used in simulation to mean that the simulation's clock runs at the same speed as a real clock. Real-time responses are often understood to be in the order of milliseconds, and sometimes microseconds. A system not specified as operating in real time cannot usually ''guarantee'' a response within any timeframe, although ''typical'' or ''expected'' response times may be given. Real-time processing ''fails'' if not completed within a specified deadline relative to an event; deadlines must always be met, regardless of system load. A real-time system has been descr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nice (Unix)
nice is a program found on Unix and Unix-like operating systems such as Linux. It directly maps to a kernel call of the same name. nice is used to invoke a utility or shell script with a particular CPU priority, thus giving the process more or less CPU time than other processes. A niceness of -20 is the highest priority and 19 is the lowest priority. The default niceness for processes is inherited from its parent process and is usually 0. Etymology ''Niceness value'' is a number attached to processes in *nix systems, that is used along with other data (such as the amount of I/O done by each process) by the kernel process scheduler to calculate a process' 'true priority'which is used to decide how much CPU time is allocated to it. The program's name, nice, is an allusion to its task of modifying a process' niceness value. The term ''niceness'' itself originates from the idea that a process with a higher niceness value is ''nicer'' to other processes in the system and to users ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Secure Attention Key
A secure attention key (SAK) or secure attention sequence (SAS) is a special key or key combination to be pressed on a computer keyboard before a login screen which must, to the user, be completely trustworthy. The operating system kernel, which interacts directly with the hardware, is able to detect whether the secure attention key has been pressed. When this event is detected, the kernel starts the trusted login processing. The secure attention key is designed to make login spoofing impossible, as the kernel will suspend any program, including those masquerading as the computer's login process, before starting a trustable login operation. Examples Some examples are: * for Windows NT. * default sequence for Linux. Not a true C2-compliant SAK. See also * Control-Alt-Del * Magic SysRq key * Break key The Break key (or the symbol ⎉) of a computer keyboard refers to breaking a telegraph circuit and originated with 19th century practice. In modern usage, the key has no w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SIGKILL
Signals are standardized messages sent to a running program to trigger specific behavior, such as quitting or error handling. They are a limited form of inter-process communication (IPC), typically used in Unix, Unix-like, and other POSIX-compliant operating systems. A signal is an asynchronous notification sent to a process or to a specific thread within the same process to notify it of an event. Common uses of signals are to interrupt, suspend, terminate or kill a process. Signals originated in 1970s Bell Labs Unix and were later specified in the POSIX standard. When a signal is sent, the operating system interrupts the target process' normal flow of execution to deliver the signal. Execution can be interrupted during any non-atomic instruction. If the process has previously registered a signal handler, that routine is executed. Otherwise, the default signal handler is executed. Embedded programs may find signals useful for inter-process communications, as signals are no ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Direct Rendering Manager
The Direct Rendering Manager (DRM) is a subsystem of the Linux kernel responsible for interfacing with GPUs of modern video cards. DRM exposes an API that user-space programs can use to send commands and data to the GPU and perform operations such as configuring the mode setting of the display. DRM was first developed as the kernel-space component of the X Server Direct Rendering Infrastructure, but since then it has been used by other graphic stack alternatives such as Wayland. User-space programs can use the DRM API to command the GPU to do hardware-accelerated 3D rendering and video decoding, as well as GPGPU computing. Overview The Linux kernel already had an API called fbdev, used to manage the framebuffer of a graphics adapter, but it couldn't be used to handle the needs of modern 3D-accelerated GPU-based video hardware. These devices usually require setting and managing a command queue in their own memory to dispatch commands to the GPU and also require management ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Out Of Memory
Out of memory (OOM) is an often undesired state of computer operation where no additional memory can be allocated for use by programs or the operating system. Such a system will be unable to load any additional programs, and since many programs may load additional data into memory during execution, these will cease to function correctly. This usually occurs because all available memory, including disk swap space, has been allocated. History Historically, the out of memory condition was more common than it is now, since early computers and operating systems were limited to small amounts of physical random-access memory (RAM) due to the inability of early processors to address large amounts of memory, as well as cost considerations. Since the advent of virtual memory opened the door for the usage of swap space, the condition is less frequent. Almost all modern programs expect to be able to allocate and deallocate memory freely at run-time, and tend to fail in uncontrolled ways (cra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
