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Log-structured File System (BSD)
The Log-Structured File System (or LFS) is an implementation of a log-structured file system (a concept originally proposed and implemented by John Ousterhout), originally developed for BSD. It was removed from FreeBSD and OpenBSD; the NetBSD implementation was nonfunctional until work leading up to the 4.0 release made it viable again as a production file system. Design Most of the on-disk format of LFS is borrowed from UFS. The indirect block, inode and directory formats are almost identical. This allows well-tested UFS file system code to be re-used; current implementations of LFS share the higher-level UFS code with the lower-level code for FFS, since both of these file systems share much in common with UFS. LFS divides the disk into ''segments'', only one of which is active at any one time. Each segment has a header called a ''summary block''. Each summary block contains a pointer to the next summary block, linking segments into one long chain that LFS treats as a line ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Log-structured File System
A log-structured filesystem is a file system in which data and metadata are written sequentially to a circular buffer, called a log. The design was first proposed in 1988 by John K. Ousterhout and Fred Douglis and first implemented in 1992 by Ousterhout and Mendel Rosenblum for the Unix-like Sprite distributed operating system. Rationale Conventional file systems lay out files with great care for spatial locality and make in-place changes to their data structures in order to perform well on optical and magnetic disks, which tend to seek relatively slowly. The design of log-structured file systems is based on the hypothesis that this will no longer be effective because ever-increasing memory sizes on modern computers would lead to I/O becoming write-heavy since reads would be almost always satisfied from memory cache. A log-structured file system thus treats its storage as a circular log and writes sequentially to the head of the log. This has several important side effe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Ousterhout
John Kenneth Ousterhout (, born October 15, 1954) is an American computer scientist. He is a professor of computer science at Stanford University. He founded Electric Cloud with John Graham-Cumming. Ousterhout was previously a professor of computer science at University of California, Berkeley, where he created the Tcl scripting language and the Tk platform-independent widget toolkit, and proposed the idea of coscheduling. Ousterhout led the research group that designed the experimental Sprite operating system and the first log-structured file system. Ousterhout also led the team that developed the Magic VLSI computer-aided design (CAD) program. Education and career He received a Bachelor of Science (B.S.) in physics from Yale University in 1975, and his Ph.D. in computer science from Carnegie Mellon University in 1980. Ousterhout received the Grace Murray Hopper Award in 1987 for his work on electronic design automation CAD systems for very-large-scale integrated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Berkeley Software Distribution
The Berkeley Software Distribution (BSD), also known as Berkeley Unix or BSD Unix, is a discontinued Unix operating system developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berkeley, beginning in 1978. It began as an improved derivative of AT&T's original Unix that was developed at Bell Labs, based on the source code but over time diverging into its own code. BSD would become a pioneer in the advancement of Unix and computing. BSD's development was begun initially by Bill Joy, who added virtual memory capability to Unix running on a VAX-11 computer. In the 1980s, BSD was widely adopted by workstation vendors in the form of proprietary Unix distributions such as DEC Ultrix and Sun Microsystems SunOS due to its permissive licensing and familiarity to many technology company founders and engineers. It also became the most popular Unix at universities, where it was used for the study of operating systems. BSD was sponsored ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FreeBSD
FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable home-class hardware, and has since continuously been the most commonly used BSD-derived operating system. FreeBSD maintains a complete system, delivering a kernel, device drivers, userland utilities, and documentation, as opposed to Linux only delivering a kernel and drivers, and relying on third-parties such as GNU for system software. The FreeBSD source code is generally released under a permissive BSD license, as opposed to the copyleft GPL used by Linux. The project includes a security team overseeing all software shipped in the base distribution. Third-party applications may be installed using the pkg package management system or from source via FreeBSD Ports. The project is supported and promoted by the FreeBSD Foundation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OpenBSD
OpenBSD is a security-focused operating system, security-focused, free software, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by fork (software development), forking NetBSD 1.0. The OpenBSD project emphasizes software portability, portability, software standard, standardization, software bug, correctness, proactive computer security, security, and integrated cryptography. The OpenBSD project maintains portable versions of many subsystems as package manager, packages for other operating systems. Because of the project's preferred BSD license, which allows binary redistributions without the source code, many components are reused in proprietary and corporate-sponsored software projects. The firewall (computing), firewall code in Apple Inc., Apple's macOS is based on OpenBSD's PF (firewall), PF firewall code, Android (operating system), Android's Bionic (software), Bionic C standard library is based on OpenBSD c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NetBSD
NetBSD is a free and open-source Unix-like operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was fork (software development), forked. It continues to be actively developed and is available for many platforms, including servers, desktops, handheld devices, and embedded systems. The NetBSD project focuses on code clarity, careful design, and portability across many computer architectures. Its source code is publicly available and Permissive free software licence, permissively licensed. History NetBSD was originally derived from the 4.3BSD-Reno release of the Berkeley Software Distribution from the Computer Systems Research Group of the University of California, Berkeley, via its Net/2 source code release and the 386BSD project. The NetBSD project began as a result of frustration within the 386BSD developer community with the pace and direction of the operating system's development. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix File System
The Unix file system (UFS) is a family of file systems supported by many Unix and Unix-like operating systems. It is a distant descendant of the original filesystem used by Version 7 Unix. Design A UFS volume is composed of the following parts: * A few blocks at the beginning of the partition reserved for boot blocks (which must be initialized separately from the filesystem) * A superblock, containing a magic number identifying this as a UFS filesystem, and some other vital numbers describing this filesystem's geometry and statistics and behavioral tuning parameters * A collection of cylinder groups. Each cylinder group has the following components: ** A backup copy of the superblock ** A cylinder group header, with statistics, free lists, etc., about this cylinder group, similar to those in the superblock ** A number of inodes, each containing file attributes ** A number of data blocks Inodes are numbered sequentially, starting at 0. Inode 0 is reserved for unalloc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inode
An inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. File-system object attributes may include metadata (times of last change, access, modification), as well as owner and permission data. A directory is a list of inodes with their assigned names. The list includes an entry for itself, its parent, and each of its children. Etymology There has been uncertainty on the Linux kernel mailing list about the reason for the "i" in "inode". In 2002, the question was brought to Unix pioneer Dennis Ritchie, who replied: A 1978 paper by Ritchie and Ken Thompson bolsters the notion of "index" being the etymological origin of inodes. They wrote: Additionally, Maurice J. Bach wrote that the word ''inode'' "is a contraction of the term index node and is commonly used in literature on the UNIX system". Details A file system ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Garbage Collection (computer Science)
In computer science, garbage collection (GC) is a form of automatic memory management. The ''garbage collector'' attempts to reclaim memory that was allocated by the program, but is no longer referenced; such memory is called ''garbage (computer science), garbage''. Garbage collection was invented by American computer scientist John McCarthy (computer scientist), John McCarthy around 1959 to simplify manual memory management in Lisp (programming language), Lisp. Garbage collection relieves the programmer from doing manual memory management, where the programmer specifies what objects to de-allocate and return to the memory system and when to do so. Other, similar techniques include stack-based memory allocation, stack allocation, region inference, and memory ownership, and combinations thereof. Garbage collection may take a significant proportion of a program's total processing time, and affect computer performance, performance as a result. Resources other than memory, such a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mount (computing)
Mounting is a process by which a computer's operating system makes Computer file, files and Directory (computing), directories on a Computer data storage, storage device (such as Hard disk drive, hard drive, CD-ROM, or network share) available for users to access via the computer's file system. In general, the process of mounting comprises the operating system acquiring access to the storage medium; recognizing, reading, and processing file system structure and metadata on it before registering them to the virtual file system (VFS) component. The location in the VFS to which the newly mounted medium was registered is called a "mount point"; when the mounting process is completed, the user can access files and directories on the medium from there. An opposite process of mounting is called unmounting, in which the operating system cuts off all user access to files and directories on the mount point, writes the remaining queue of user data to the storage device, refreshes file sys ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File System Fragmentation
In computing, file system fragmentation, sometimes called file system aging, is the tendency of a file system to lay out the contents of Computer file, files non-continuously to allow in-place modification of their contents. It is a special case of fragmentation (computer)#Data fragmentation, data fragmentation. File system fragmentation negatively impacts seek time in spinning storage media, which is known to hinder throughput (disk drive), throughput. Fragmentation can be remedied by re-organizing files and free space back into contiguous areas, a process called defragmentation. Solid-state drives do not physically seek, so their non-sequential data access is hundreds of times faster than moving drives, making fragmentation less of an issue. It is recommended to not manually defragment solid-state storage, because this can prematurely wear drives via unnecessary write–erase operations. Causes When Disk formatting, a file system is first initialized on a Disk partitioning, parti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Design Rationale
A design rationale is an explicit documentation of the reasons behind decisions made when designing a system or artifact. As initially developed by W.R. Kunz and Horst Rittel, design rationale seeks to provide argumentation-based structure to the political, collaborative process of addressing wicked problems. Overview A design rationale is the explicit listing of decisions made during a design process, and the reasons why those decisions were made.Jarczyk, Alex P.; Löffler, Peter; Shipman III, Frank M. (1992), "Design Rationale for Software Engineering: A Survey", ''25th Hawaii International Conference on System Sciences'', 2, pp. 577-586 Its primary goal is to support designers by providing a means to record and communicate the argumentation and reasoning behind the design process.Horner, J.; Atwood, M.E. (2006), "Effective Design Rationale: Understanding the Barriers", in Dutoit, A.H.; McCall, R.; Mistrík, I. et al., Rationale Management in Software Engineering, Spr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
