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QCOW
qcow is a file format for disk image files used by QEMU, a hosted virtual machine monitor. It stands for "QEMU Copy On Write" and uses a disk storage optimization strategy that delays allocation of storage until it is actually needed. Files in qcow format can contain a variety of disk images which are generally associated with specific guest operating systems. Three versions of the format exist: qcow, qcow2 and qcow3 which use the ''.qcow'', ''.qcow2'' and ''.qcow3'' file extensions, respectively. qemu-img command allows to inspect, check, create, convert, resize and take snapshot of qcow images. The e2fsprogs command e2image also has support for generating qcow2 files to avoid the use of sparse file support. Features One of the main characteristics of qcow disk images is that files with this format can grow as data is added. This allows for smaller file sizes than raw disk images, which allocate the whole image space to a file, even if parts of it are empty. This is particu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
QEMU
QEMU is a free and open-source emulator (Quick EMUlator). It emulates the machine's processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it to run a variety of guest operating systems. It can interoperate with Kernel-based Virtual Machine (KVM) to run virtual machines at near-native speed. QEMU can also do emulation for user-level processes, allowing applications compiled for one architecture to run on another. Licensing QEMU was written by Fabrice Bellard and is free software, mainly licensed under the GNU General Public License (GPL for short). Various parts are released under the BSD license, GNU Lesser General Public License (LGPL) or other GPL-compatible licenses. Operating modes QEMU has multiple operating modes: ;User-mode emulation: In this mode QEMU runs single Linux or Darwin/macOS programs that were compiled for a different instruction set. System calls are thunked for endianness and for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File Format
A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free. Some file formats are designed for very particular types of data: PNG files, for example, store bitmapped images using lossless data compression. Other file formats, however, are designed for storage of several different types of data: the Ogg format can act as a container for different types of multimedia including any combination of audio and video, with or without text (such as subtitles), and metadata. A text file can contain any stream of characters, including possible control characters, and is encoded in one of various character encoding schemes. Some file formats, such as HTML, scalable vector graphics, and the source code of computer software are text files with defined syntaxes that allow them to be used for specific purposes. Specifications ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disk Image
A disk image, in computing, is a computer file containing the contents and structure of a disk volume or of an entire data storage device, such as a hard disk drive, tape drive, floppy disk, optical disc, or USB flash drive. A disk image is usually made by creating a sector-by-sector copy of the source medium, thereby perfectly replicating the structure and contents of a storage device independent of the file system. Depending on the disk image format, a disk image may span one or more computer files. The file format may be an open standard, such as the ISO image format for optical disc images, or a disk image may be unique to a particular software application. The size of a disk image can be large because it contains the contents of an entire disk. To reduce storage requirements, if an imaging utility is filesystem-aware it can omit copying unused space, and it can compress the used space. History Disk images were originally (in the late 1960s) used for backup and disk clo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virtual Machine Monitor
A hypervisor (also known as a virtual machine monitor, VMM, or virtualizer) is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called a ''host machine'', and each virtual machine is called a ''guest machine''. The hypervisor presents the guest operating systems with a virtual operating platform and manages the execution of the guest operating systems. Unlike an emulator, the guest executes most instructions on the native hardware. Multiple instances of a variety of operating systems may share the virtualized hardware resources: for example, Linux, Windows, and macOS instances can all run on a single physical x86 machine. This contrasts with operating-system–level virtualization, where all instances (usually called ''containers'') must share a single kernel, though the guest operating systems can differ in user space, such as different Linux distributions with the sa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Copy-on-write
Copy-on-write (COW), sometimes referred to as implicit sharing or shadowing, is a resource-management technique used in computer programming to efficiently implement a "duplicate" or "copy" operation on modifiable resources. If a resource is duplicated but not modified, it is not necessary to create a new resource; the resource can be shared between the copy and the original. Modifications must still create a copy, hence the technique: the copy operation is deferred until the first write. By sharing resources in this way, it is possible to significantly reduce the resource consumption of unmodified copies, while adding a small overhead to resource-modifying operations. In virtual memory management Copy-on-write finds its main use in sharing the virtual memory of operating system processes, in the implementation of the fork system call. Typically, the process does not modify any memory and immediately executes a new process, replacing the address space entirely. Thus, it would be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Operating Systems
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer from cellular phones and video game consoles to web servers and supercomputers. The dominant general-purpose personal computer operating system is Microsoft Windows with a market share of around 74.99%. macOS by Apple Inc. is in second place (14.84%), and th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
E2fsprogs
e2fsprogs (sometimes called the e2fs programs) is a set of utilities for maintaining the ext2, ext3 and ext4 file systems. Since those file systems are often the default for Linux distributions, it is commonly considered to be essential software. List of utilities Included with e2fsprogs, ordered by ASCIIbetical order, are: ;badblocks : search a device for bad blocks ;blkid : locate/print block device attributes ;chattr : change file attributes on a Linux file system ;debugfs : used to manually view or modify internal structures of the file system ;dumpe2fs : which prints superblock and block group information. ;e2freefrag : report free space fragmentation information ;e2fsck : an fsck program that checks for and corrects inconsistencies ;e2image : save critical ext2/ext3/ext4 filesystem metadata to a file ;e2label : change the label on an ext2/ext3/ext4 filesystem ;e2undo : replay an undo log for an ext2/ext3/ext4 filesystem ;e4defrag : online defragmenter for ext4 filesystem ;fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IMG (file Format)
IMG, in computing, refers to binary files with the .img filename extension that store raw disk images of floppy disks, hard drives, and optical discs or a bitmap image – .img. Overview The .img filename extension is used by disk image files, which contain raw dumps of a magnetic disk or of an optical disc. Since a raw image consists of a sector-by-sector binary copy of the source medium, the actual format of the file contents will depend on the file system of the disk from which the image was created (such as a version of FAT). Raw disk images of optical media (such as CDs and DVDs) contain a raw image of all the tracks in a disc (which can include audio, data and video tracks). In the case of CD-ROMs and DVDs, these images usually include not only the data from each sector, but the control headers and error correction fields for each sector as well. Since IMG files hold no additional data beyond the disk contents, these files can only be automatically handled by programs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File System
In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one large body of data with no way to tell where one piece of data stopped and the next began, or where any piece of data was located when it was time to retrieve it. By separating the data into pieces and giving each piece a name, the data are easily isolated and identified. Taking its name from the way a paper-based data management system is named, each group of data is called a "file". The structure and logic rules used to manage the groups of data and their names is called a "file system." There are many kinds of file systems, each with unique structure and logic, properties of speed, flexibility, security, size and more. Some file systems have been designed to be used for specific applications. For example, the ISO 9660 file system is designe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sparse File
In computer science, a sparse file is a type of computer file that attempts to use file system space more efficiently when the file itself is partially empty. This is achieved by writing brief information ( metadata) ''representing'' the empty blocks to the data storage media instead of the actual "empty" space which makes up the block, thus consuming less storage space. The full block size is written to the media as the actual size only when the block contains "real" (non-empty) data. When reading sparse files, the file system transparently converts metadata representing empty blocks into "real" blocks filled with null bytes at runtime. The application is unaware of this conversion. Most modern file systems support sparse files, including most Unix variants and NTFS. Apple's HFS+ does not provide support for sparse files, but in OS X, the virtual file system layer supports storing them in any supported file system, including HFS+. Apple File System (APFS), announced in June 2016 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FAT32
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by current operating systems for personal computers and many mobile devices and embedded systems, allowing interchange of data between disparate systems. The increase in disk drives capacity required three major variants: FAT12, FAT16 and FAT32. The FAT standard has also been expanded in other ways while generally preserving backward compatibility with existing software. FAT is no longer the default file system for Microsoft Windows computers. FAT file systems are still commonly found on floppy disks, flash and other solid-state memory cards and modules (including USB flash drives), as well as many portable and embedded devices. FAT is the standard file system for digital cameras per the DCF specification. Overview Concepts ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zlib
zlib ( or "zeta-lib", ) is a software library used for data compression. zlib was written by Jean-loup Gailly and Mark Adler and is an abstraction of the DEFLATE compression algorithm used in their gzip file compression program. zlib is also a crucial component of many software platforms, including Linux, macOS, and iOS. It has also been used in gaming consoles such as the PlayStation 4, PlayStation 3, Wii U, Wii, Xbox One and Xbox 360. The first public version of zlib, 0.9, was released on 1 May 1995 and was originally intended for use with the libpng image library. It is free software, distributed under the zlib License. Capabilities Encapsulation zlib compressed data are typically written with a gzip or a zlib wrapper. The wrapper encapsulates the raw DEFLATE data by adding a header and trailer. This provides stream identification and error detection that are not provided by the raw DEFLATE data. The gzip header, used in the ubiquitous gzip file format, is larger than ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
