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In computing, a system image is a serialized copy of the entire state of a computer system stored in some non-volatile form such as a file. A system is said to be capable of using system images if it can be shut down and later restored to exactly the same state. In such cases, system images can be used for backup.
Hibernation is an example that uses an image of the entire machine's RAM.
If a system has all its state written to a disk, then a system image can be produced by simply copying that disk to a file elsewhere, often with disk cloning applications. On many systems a complete system image cannot be created by a disk cloning program running within that system because information can be held outside of disks and volatile memory, for example in non-volatile memory like boot ROMs.
A process image is a copy of a given process's state at a given point in time. It is often used to create persistence within an otherwise volatile system. A common example is a database management system (DBMS). Most DBMS can store the state of its database or databases to a file before being closed down (see database dump). The DBMS can then be restarted later with the information in the database intact and proceed as though the software had never stopped. Another example would be the hibernate feature of many operating systems. Here, the state of all RAM memory is stored to disk, the computer is brought into an energy saving mode, then later restored to normal operation.
Some emulators provide a facility to save an image of the system being emulated. In video gaming this is often referred to as a savestate.
Another use is code mobility: a mobile agent can migrate between machines by having its state saved, then copying the data to another machine and restarting there.
Some programming languages provide a command to take a system image of a program. This is normally a standard feature in Smalltalk (inspired by FLEX) and Lisp, among other languages. Development in these languages is often quite different from many other programming languages. For example, in Lisp the programmer may load packages or other code into a running Lisp implementation using the read-eval-print loop, which usually compiles the programs. Data is loaded into the running Lisp system. The programmer may then dump a system image, containing that pre-compiled and possibly customized code—and also all loaded application data. Often this image is an executable, and can be run on other machines. This system image can be the form in which executable programs are distributed—this method has often been used by programs (such as TeX and Emacs) largely implemented in Lisp, Smalltalk, or idiosyncratic languages to avoid spending time repeating the same initialization work every time they start up.
Similar, Lisp Machines were booted from Lisp images, called Worlds. The World contains the complete operating system, its applications and its data in a single file. It was also possible to save incremental Worlds, that contain only the changes from some base World. Before saving the World, the Lisp Machine operating system could optimize the contents of memory (better memory layout, compacting data structures, sorting data, ...).
Although its purpose is different, a "system image" is often similar in structure to a core dump.
A computer program is a collection of instructions that can be executed by a computer to perform a specific task.
In computing, a database is an organized collection of data stored and accessed electronically from a computer system. Where databases are more complex they are often developed using formal design and modeling techniques.
Lisp is a family of programming languages with a long history and a distinctive, fully parenthesized prefix notation. Originally specified in 1958, Lisp is the second-oldest high-level programming language. Only Fortran is older, by one year. Lisp has changed since its early days, and many dialects have existed over its history. Today, the best-known general-purpose Lisp dialects are Racket, Common Lisp, Scheme, and Clojure.
An object database is a database management system in which information is represented in the form of objects as used in object-oriented programming. Object databases are different from relational databases which are table-oriented. Object–relational databases are a hybrid of both approaches.
Smalltalk is an object-oriented, dynamically typed reflective programming language. Smalltalk was created as the language underpinning the "new world" of computing exemplified by "human–computer symbiosis". It was designed and created in part for educational use, specifically for constructionist learning, at the Learning Research Group (LRG) of Xerox PARC by Alan Kay, Dan Ingalls, Adele Goldberg, Ted Kaehler, Diana Merry, Scott Wallace, and others during the 1970s.
In computing, serialization or serialisation is the process of translating a data structure or object state into a format that can be stored or transmitted and reconstructed later. When the resulting series of bits is reread according to the serialization format, it can be used to create a semantically identical clone of the original object. For many complex objects, such as those that make extensive use of references, this process is not straightforward. Serialization of object-oriented objects does not include any of their associated methods with which they were previously linked.
In computing, a core dump, memory dump, crash dump, system dump, or ABEND dump consists of the recorded state of the working memory of a computer program at a specific time, generally when the program has crashed or otherwise terminated abnormally. In practice, other key pieces of program state are usually dumped at the same time, including the processor registers, which may include the program counter and stack pointer, memory management information, and other processor and operating system flags and information. A snapshot dump is a memory dump requested by the computer operator or by the running program, after which the program is able to continue. Core dumps are often used to assist in diagnosing and debugging errors in computer programs.
In computer science, an interpreter is a computer program that directly executes instructions written in a programming or scripting language, without requiring them previously to have been compiled into a machine language program. An interpreter generally uses one of the following strategies for program execution:
Genera is a commercial operating system and integrated development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the Massachusetts Institute of Technology (MIT) AI Lab's Lisp machines which Symbolics had used in common with Lisp Machines, Inc. (LMI), and Texas Instruments (TI). Genera is also sold by Symbolics as Open Genera, which runs Genera on computers based on a Digital Equipment Corporation (DEC) Alpha processor using Tru64 UNIX. It is released and licensed as proprietary software.
In programming languages, a closure, also lexical closure or function closure, is a technique for implementing lexically scoped name binding in a language with first-class functions. Operationally, a closure is a record storing a function together with an environment. The environment is a mapping associating each free variable of the function with the value or reference to which the name was bound when the closure was created. Unlike a plain function, a closure allows the function to access those captured variables through the closure's copies of their values or references, even when the function is invoked outside their scope.
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.
Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms.
An object-oriented operating system is an operating system that is designed, structured, and operated using object-oriented programming principles.
ISAM is a method for creating, maintaining, and manipulating computer files of data so that records can be retrieved sequentially or randomly by one or more keys. Indexes of key fields are maintained to achieve fast retrieval of required file records in Indexed files. IBM originally developed ISAM for mainframe computers, but implementations are available for most computer systems.
A ROM image, or ROM file, is a computer file which contains a copy of the data from a read-only memory chip, often from a video game cartridge, or used to contain a computer's firmware, or from an arcade game's main board. The term is frequently used in the context of emulation, whereby older games or firmware are copied to ROM files on modern computers and can, using a piece of software known as an emulator, be run on a different device than which they were designed for. ROM burners are used to copy ROM images to hardware, such as ROM cartridges, or ROM chips, for debugging and QA testing.
Hibernation in computing is powering down a computer while retaining its state. When hibernation begins, the computer saves the contents of its random access memory (RAM) to a hard disk or other non-volatile storage. When the computer is turned on the RAM is restored and the computer is exactly as it was before entering hibernation. Hibernation was first implemented in 1992 and patented by Compaq Computer Corporation in Houston, Texas. As of 2020, Microsoft's Windows 10 employs a type of hibernation by default when shutting down.
In computer science, persistence refers to the characteristic of state of a system that outlives the process that created it. This is achieved in practice by storing the state as data in computer data storage. Programs have to transfer data to and from storage devices and have to provide mappings from the native programming-language data structures to the storage device data structures.
Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing software that is rarely changed during the life of the system, also known as firmware. Software applications for programmable devices can be distributed as plug-in cartridges containing ROM.
Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code: data in the form of fields, and code, in the form of procedures.