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A Database Management System (DBMS) is a set of computer programs that controls the creation, maintenance, and the use of adatabase. It allows organizations to place control of database development in the hands of database administrators (DBAs) and other specialists   (Dell XPS M1210 Batteryhttp://www.hdd-shop.co.uk .

A DBMS is a system software package that helps the use of integrated collection of data records and files known as databases. It allows different user application programs to easily access the same database. DBMSs may use any of a variety ofdatabase models, such as the network model or relational model   Dell Studio XPS 1640 Battery .

In large systems, a DBMS allows users and other software to store and retrieve data in a structured way. Instead of having to write computer programs to extract information, user can ask simple questions in a query language. Thus, many DBMS packages provide Fourth-generation programming language (4GLs) and other application development features  Dell Vostro 1710 Battery .

It helps to specify the logical organization for a database and access and use the information within a database. It provides facilities for controlling data access, enforcing data integrity, managing concurrency, and restoring the database from backups. A DBMS also provides the ability to logically present database information to users   Dell KM958 battery .

Overview

A DBMS is a set of software programs that controls the organization, storage, management, and retrieval of data in a database. DBMSs are categorized according to their data structures or types    Dell Studio 1555 battery .

The DBMS accepts requests for data from an application program and instructs the operating system to transfer the appropriate data. The queries and responses must be submitted and received according to a format that conforms to one or more applicable protocols. When a DBMS is used, information systems can be changed more easily as the organization's information requirements change  Sony VGP-BPS13 battery .

New categories of data can be added to the database without disruption to the existing system.

Database servers are dedicated computers that hold the actual databases and run only the DBMS and related software. Database servers are usually multiprocessor computers, with generous memory and RAID disk arrays used for stable storage   Sony VGP-BPS13/B battery .

Hardware database accelerators, connected to one or more servers via a high-speed channel, are also used in large volume transaction processing environments. DBMSs are found at the heart of most database applications. DBMSs may be built around a custom multitasking kernel with built-in networking support, but modern DBMSs typically rely on a standard operating system to provide these functions   Sony VGP-BPS13/S battery .

History

Databases have been in use since the earliest days of electronic computing. Unlike modern systems which can be applied to widely different databases and needs, the vast majority of older systems were tightly linked to the custom databases in order to gain speed at the expense of flexibility   Sony VGP-BPS13A/B battery .

Originally DBMSs were found only in large organizations with the computer hardware needed to support large data sets.

1960s Navigational DBMS

As computers grew in speed and capability, a number of general-purpose database systems emerged; by the mid-1960s there were a number of such systems in commercial use   Sony VGP-BPS13B/B battery .

Interest in a standard began to grow, and Charles Bachman, author of one such product, the Integrated Data Store (IDS), founded the "Database Task Group" within CODASYL, the group responsible for the creation and standardization of COBOL. In 1971 they delivered their standard     Sony VGP-BPL9 battery ,

which generally became known as the "Codasyl approach", and soon a number of commercial products based on this approach were made available.

The Codasyl approach was based on the "manual" navigation of a linked data set which was formed into a large network  Sony VGP-BPS13B/B battery .

When the database was first opened, the program was handed back a link to the first record in the database, which also contained pointers to other pieces of data. To find any particular record the programmer had to step through these pointers one at a time until the required record was returned   Sony VGP-BPL15 battery .

Simple queries like "find all the people in India" required the program to walk the entire data set and collect the matching results one by one. There was, essentially, no concept of "find" or "search". This may sound like a serious limitation today, but in an era when most data was stored on magnetic tape such operations were too expensive to contemplate anyway  Dell Inspiron E1505 battery .

IBM also had their own DBMS system in 1968, known as IMS. IMS was a development of software written for the Apollo program on the System/360. IMS was generally similar in concept to Codasyl, but used a strict hierarchy for its model of data navigation instead of Codasyl's network model     Dell Latitude E6400 battery .

Both concepts later became known as navigational databases due to the way data was accessed, and Bachman's 1973 Turing Award award presentation was The Programmer as Navigator. IMS is classified as a hierarchical database. IMS and IDMS, both CODASYL databases, as well as CINCOMs TOTAL database, are classified as network databases  HP Pavilion dv6000 Battery .

1970s Relational DBMS

Edgar Codd worked at IBM in San Jose, California, in one of their offshoot offices that was primarily involved in the development of hard disk systems. He was unhappy with the navigational model of the Codasyl approach, notably the lack of a "search" facility  SONY VAIO VGN-FZ Battery .

In 1970, he wrote a number of papers that outlined a new approach to database construction that eventually culminated in the groundbreaking A Relational Model of Data for Large Shared Data Banks.

In this paper, he described a new system for storing and working with large databases   SONY VAIO VGN-FZ18 Battery .

Instead of records being stored in some sort of linked list of free-form records as in Codasyl, Codd's idea was to use a "table" of fixed-length records. A linked-list system would be very inefficient when storing "sparse" databases where some of the data for any one record could be left empty     SONY VAIO VGN-FZ21E Battery .

The relational model solved this by splitting the data into a series of normalized tables, with optional elements being moved out of the main table to where they would take up room only if needed.

In the relational model, related records are linked together with a "key"       SONY VAIO VGN-FW21E Battery .

For instance, a common use of a database system is to track information about users, their name, login information, various addresses and phone numbers. In the navigational approach all of these data would be placed in a single record, and unused items would simply not be placed in the database       SONY VAIO VGN-NR11S/S Battery .

In the relational approach, the data would be normalized into a user table, an address table and a phone number table (for instance). Records would be created in these optional tables only if the address or phone numbers were actually provided.

Linking the information back together is the key to this system       SONY VAIO VGN-NR11M/S Battery .

In the relational model, some bit of information was used as a "key", uniquely defining a particular record. When information was being collected about a user, information stored in the optional (or related) tables would be found by searching for this key. For instance       SONY VAIO VGN-NR11Z/S Battery ,

if the login name of a user is unique, addresses and phone numbers for that user would be recorded with the login name as its key. This "re-linking" of related data back into a single collection is something that traditional computer languages are not designed for  SONY VAIO VGN-NR11Z/T Battery .

Just as the navigational approach would require programs to loop in order to collect records, the relational approach would require loops to collect information about any one record. Codd's solution to the necessary looping was a set-oriented language, a suggestion that would later spawn the ubiquitous SQL        Sony VAIO VGN-FZ21E Battery .

Using a branch of mathematics known as tuple calculus, he demonstrated that such a system could support all the operations of normal databases (inserting, updating etc.) as well as providing a simple system for finding and returning sets of data in a single operation     Sony VAIO VGN-FW21E Battery .

Codd's paper was picked up by two people at Berkeley, Eugene Wong and Michael Stonebraker. They started a project known as INGRESusing funding that had already been allocated for a geographical database project, using student programmers to produce code      Sony VAIO VGN-NR11S/S Battery .

Beginning in 1973, INGRES delivered its first test products which were generally ready for widespread use in 1979. During this time, a number of people had moved "through" the group — perhaps as many as 30 people worked on the project, about five at a time  Sony VAIO VGN-NR11Z/S Battery .

INGRES was similar to System R in a number of ways, including the use of a "language" for data access, known as QUEL — QUEL was in fact relational, having been based on Codd's own Alpha language, but has since been corrupted to follow SQL, thus violating much the same concepts of the relational model as SQL itself   Sony VAIO VGN-NR11M/S Battery .

IBM itself did one test implementation of the relational model, PRTV, and a production one, Business System 12, both now discontinued. Honeywell did MRDS for Multics, and now there are two new implementations: Alphora Dataphor and Rel. All other DBMS implementations usually called relational are actually SQL DBMSs       Sony VAIO VGN-NR11Z/T Battery .

In 1968, the University of Michigan began development of the Micro DBMS . It was used to manage very large data sets by the US Department of Labor, the Environmental Protection Agency and researchers from University of Alberta, the University of Michigan and Wayne State University       SONY VAIO VGN-FZ180E Battery .

It ran on mainframe computers using Michigan Terminal System. The system remained in production until 1996.

End 1970s SQL DBMS

IBM started working on a prototype system loosely based on Codd's concepts as System R in the early 1970s. The first version was ready in 1974/5, and work then started on multi-table systems in which the data could be split so that all of the data for a record (some of which is optional) did not have to be stored in a single large "chunk"   SONY VAIO VGN-FZ220E Battery .

Subsequent multi-user versions were tested by customers in 1978 and 1979, by which time a standardized query language - SQL - had been added. Codd's ideas were establishing themselves as both workable and superior to Codasyl, pushing IBM to develop a true production version of System R, known as SQL/DS, and, later, Database 2 (DB2)   SONY VAIO VGN-FZ340E Battery .

Many of the people involved with INGRES became convinced of the future commercial success of such systems, and formed their own companies to commercialize the work but with an SQL interface.Sybase, Informix, NonStop SQL and eventually Ingres itself were all being sold as offshoots to the original INGRES product in the 1980s      SONY VAIO VGN-FZ430E Battery .

Even Microsoft SQL Server is actually a re-built version of Sybase, and thus, INGRES. Only Larry Ellison's Oracle started from a different chain, based on IBM's papers on System R, and beat IBM to market when the first version was released in 1978    SONY VAIO VGN-FZ460E Battery .

Stonebraker went on to apply the lessons from INGRES to develop a new database, Postgres, which is now known as PostgreSQL. PostgreSQL is often used for global mission critical applications (the .org and .info domain name registries use it as their primary data store, as do many large companies and financial institutions)       SONY VAIO VGN-FZ480E Battery .

In Sweden, Codd's paper was also read and Mimer SQL was developed from the mid-70s at Uppsala University. In 1984, this project was consolidated into an independent enterprise. In the early 1980s, Mimer introduced transaction handling for high robustness in applications, an idea that was subsequently implemented on most other DBMS      SONY VAIO VGN-FZ4000 Battery .

1980s Object Oriented Databases

The 1980s, along with a rise in object oriented programming, saw a growth in how data in various databases were handled. Programmers and designers began to treat the data in their databases as objects      SONY VAIO VGN-FZ31E Battery .

That is to say that if a person's data were in a database, that person's attributes, such as their address, phone number, and age, were now considered to belong to that person instead of being extraneous data. This allows for relationships between data to be relation to objects and their attributes and not to individual fields     SONY VAIO VGN-FZ31B Battery .

Another big game changer for databases in the 1980s was the focus on increasing reliability and access speeds. In 1989, two professors from the University of Michigan at Madison published an article at an ACM associated conference outlining their methods on increasing database performance      SONY VAIO VGN-FZ31J Battery .

The idea was to replicate specific important, and often queried information, and store it in a smaller temporary database that linked these key features back to the main database. This meant that a query could search the smaller database much quicker, rather than search the entire dataset       SONY VAIO VGN-FZ31M Battery .

This eventually leads to the practice of indexing, which is used by almost every operating system from Windows to the system that operates Apple iPod devices.

Current trends

In 1998, database management was in need of a new style of databases to solve current database management problems  SONY VAIO VGN-FZ31Z Battery .

Researchers realized that the old trends of database management were becoming too complex and there was a need for automated configuration and management. Surajit Chaudhuri, Gerhard Weikum and Michael Stonebraker were the pioneers that dramatically affected the thought of database management systems     SONY VAIO VGN-FZ38M Battery .

They believed that database management needed a more modular approach and there were too many specifications needed for users. Since this new development process of database management there are more possibilities. Database management is no longer limited to “monolithic entities”        SONY VGP-BPS8 Battery .

Many solutions have been developed to satisfy the individual needs of users. The development of numerous database options has created flexibility in database management.

There are several ways database management has affected the field of technology       SONY VGP-BPS13/S Battery .

Because organizations' demand for directory services has grown as they expand in size, businesses use directory services that provide prompted searches for company information. Mobile devices are able to store more than just the contact information of users, and can cache and display a large amount of information on smaller displays      SONY VGP-BPS13A/B Battery .

Search engine queries are able to locate data within the World Wide Web. Retailers have also benefited from the developments with data warehousing, recording customer transactions. Online transactions have become tremendously popular for e-business. Consumers and businesses are able to make payments securely through some company websites  SONY VGP-BPS13B/B Battery .

These current developments would not have been possible without the evolution of database management. Even with the progress of database management, there is a demonstrated need for new development as specifications and needs change.

As the speeds of consumer internet connectivity increase        SONY VGP-BPS13A/S Battery ,

and as data availability and computing become more ubiquitous, databases are seeing a migration to web services. Web-based languages such as XML and PHP are used to process databases. These languages allow databases to live in "the cloud." As with products such as Google's Gmail         SONY VGP-BPS13AS Battery ,

Microsoft's Office 2010, and Carbonite's online backup services, many services are beginning to move to web based services due to increasing internet reliability, data storage efficiency, and the lack of a need for dedicated IT staff to manage the hardware    Dell Inspiron 1320n Battery .

Faculty at Rochester Institute of Technology published a paper regarding the use of databases in the cloud and state that their university plans to add cloud-based database computing to their curriculum to "keep [their] information technology (IT) curriculum at the forefront of technology       Dell Inspiron 1464 Battery ."

Building blocks

Components

  • DBMS Engine accepts logical requests from various other DBMS subsystems, converts them into physical equivalents, and actually accesses the database and data dictionary as they exist on a storage device  Dell Inspiron 1564 Battery .
  • Data Definition Subsystem helps the user create and maintain the data dictionary and define the structure of the files in a database.
  • Data Manipulation Subsystem helps the user to add, change, and delete information in a database and query it for valuable information       Dell Inspiron 1764 Battery .
  • Software tools within the data manipulation subsystem are most often the primary interface between user and the information contained in a database. It allows the user to specify its logical information requirements.
  • Application Generation Subsystem contains facilities to help users develop transaction-intensive applications  Dell Studio 1450 Battery .
  • It usually requires that the user perform a detailed series of tasks to process a transaction. It facilitates easy-to-use data entry screens, programming languages, and interfaces.
  • Data Administration Subsystem helps users manage the overall database environment by providing facilities for backup and recovery, security management, query optimization, concurrency control, and change management  Dell Studio 1457 Battery .

Modeling language

A modeling language is a data modeling language to define the schema of each database hosted in the DBMS, according to the DBMS database model. Database management systems (DBMS) are designed to use one of five database structures to provide simplistic access to information stored in databases       Dell Latitude D610 Battery .

The five database structures are:

  • the hierarchical model,
  • the network model,
  • the relational model,
  • the multidimensional model, and
  • the object model       Toshiba NB100 Battery .

Inverted lists and other methods are also used. A given database management system may provide one or more of the five models. The optimal structure depends on the natural organization of the application's data, and on the application's requirements, which include transaction rate (speed), reliability, maintainability, scalability, and cost      Toshiba Satellite M65 battery .

The hierarchical structure was used in early mainframe DBMS. Records’ relationships form a treelike model. This structure is simple but nonflexible because the relationship is confined to a one-to-many relationship. IBM’s IMS system and the RDM Mobile are examples of a hierarchical database system with multiple hierarchies over the same data      Toshiba Satellite M60 battery .

RDM Mobile is a newly designed embedded database for a mobile computer system. The hierarchical structure is used primarily today for storing geographic information and file systems.

The network structure consists of more complex relationships      Dell Latitude D830 Battery .

Unlike the hierarchical structure, it can relate to many records and accesses them by following one of several paths. In other words, this structure allows for many-to-many relationships.

The relational structure is the most commonly used today. It is used by mainframe, midrange and microcomputer systems  Dell Latitude D620 Battery .

It uses two-dimensional rows and columns to store data. The tables of records can be connected by common key values. While working for IBM, E.F. Codd designed this structure in 1970. The model is not easy for the end user to run queries with because it may require a complex combination of many tables       Dell Inspiron Mini 10 Battery .

The multidimensional structure is similar to the relational model. The dimensions of the cube-like model have data relating to elements in each cell. This structure gives a spreadsheet-like view of data. This structure is easy to maintain because records are stored as fundamental attributes - in the same way they are viewed - and the structure is easy to understand     Sony VGN-FW11S Battery .

Its high performance has made it the most popular database structure when it comes to enabling online analytical processing (OLAP).

The object oriented structure has the ability to handle graphics, pictures, voice and text, types of data, without difficultly unlike the other database structures        Sony VGN-FW11M Battery .

This structure is popular for multimediaWeb-based applications. It was designed to work with object-oriented programming languages such as Java        Sony VGN-FW139E/H battery .

The dominant model in use today is the ad hoc one embedded in SQL, despite the objections of purists who believe this model is a corruption of the relational model since it violates several fundamental principles for the sake of practicality and performance. Many DBMSs also support the Open Database Connectivity API that supports a standard way for programmers to access the DBMS  Dell Latitude E5400 Battery .

Before the database management approach, organizations relied on file processing systems to organize, store, and process data files. End users criticized file processing because the data is stored in many different files and each organized in a different way. Each file was specialized to be used with a specific application     Dell Latitude E4200 Battery .

File processing was bulky, costly and nonflexible when it came to supplying needed data accurately and promptly. Data redundancy is an issue with the file processing system because the independent data files produce duplicate data so when updates were needed each separate file would need to be updated       Dell Inspiron 300M Battery .

Another issue is the lack of data integration. The data is dependent on other data to organize and store it. Lastly, there was not any consistency or standardization of the data in a file processing system which makes maintenance difficult. For these reasons, the database management approach was produced        Dell Vostro A840 Battery .

Data structure

Data structures (fields, records, files and objects) optimized to deal with very large amounts of data stored on a permanent data storage device (which implies relatively slow access compared to volatile main memory)       Dell Studio 1737 battery .

Database query language

A database query language and report object allows users to interactively interrogate the database, analyze its data and update it according to the users privileges on data. It also controls the security of the database       Dell Inspiron E1505 battery .

Data security prevents unauthorized users from viewing or updating the database. Using passwords, users are allowed access to the entire database or subsets of it calledsubschemas. For example, an employee database can contain all the data about an individual employee, but one group of users may be authorized to view only payroll data, while others are allowed access to only work history and medical data    Dell RM791 battery .

If the DBMS provides a way to interactively enter and update the database, as well as interrogate it, this capability allows for managing personal databases. However, it may not leave an audit trail of actions or provide the kinds of controls necessary in a multi-user organization      Dell XPS M1530 battery .

These controls are only available when a set of application programs are customized for each data entry and updating function.

Transaction mechanism

A database transaction mechanism ideally guarantees ACID properties in order to ensure data integrity despite concurrent user accesses (concurrency control), and faults (fault tolerance)       Dell XPS M2010 battery .

It also maintains the integrity of the data in the database. The DBMS can maintain the integrity of the database by not allowing more than one user to update the same record at the same time. The DBMS can help prevent duplicate records via unique index constraints; for example, no two customers with the same customer numbers (key fields) can be entered into the database  Acer Aspire One battery .

See ACID properties for more information (Redundancy avoidance).

Topics

External, Logical and Internal view

A database management system provides the ability for many different users to share data and process resources  Toshiba Satellite P10 Battery .

As there can be many different users, there are many different database needs. The question is: How can a single, unified database meet varying requirements of so many users      SONY VGN-FZ210CE Battery ?

A DBMS minimizes these problems by providing three views of the database data: an external view (or user view), logical view (or conceptual view) and physical (or internal) view. The user’s view of a database program represents data in a format that is meaningful to a user and to the software programs that process those data       Dell Precision M70 Battery .

One strength of a DBMS is that while there is typically only one conceptual (or logical) and physical (or internal) view of the data, there can be an endless number of different external views. This feature allows users to see database information in a more business-related way rather than from a technical, processing viewpoint     Toshiba Satellite L305 Battery .

Thus the logical view refers to the way the user views the data, and the physical view refers to the way the data are physically stored and processed.

Features and capabilities

Alternatively, and especially in connection with the relational model of database management, the relation between attributes drawn from a specified set of domains can be seen as being primary       Toshiba Satellite T4900 Battery .

For instance, the database might indicate that a car that was originally "red" might fade to "pink" in time, provided it was of some particular "make" with an inferior paint job. Such higher arity relationships provide information on all of the underlying domains at the same time, with none of them being privileged above the others          Toshiba PA3399U-2BRS battery .

Simple definition

A database management system is the system in which related data is stored in an efficient and compact manner. "Efficient" means that the data which is stored in the DBMS can be accessed quickly and "compact" means that the data takes up very little space in the computer's memory     Toshiba Satellite A200 Battery .

The phrase "related data" is means that the data stored pertains to a particular topic.

Specialized databases have existed for scientific, imaging, document storage and like uses. Functionality drawn from such applications has begun appearing in mainstream DBMS's as well        Toshiba Satellite 1200 Battery .

However, the main focus, at least when aimed at the commercial data processing market, is still on descriptive attributes on repetitive record structures.

Thus, the DBMSs of today roll together frequently needed services or features of attribute management  Toshiba Satellite M300 Battery .

By externalizing such functionality to the DBMS, applications effectively share code with each other and are relieved of much internal complexity. Features commonly offered by database management systems include        SONY VGP-BPS13A/Q Battery :

Query ability

Querying is the process of requesting attribute information from various perspectives and combinations of factors. Example: "How many 2-door cars in Texas are green?" A database query language and report writer allow users to interactively interrogate the database, analyze its data and update it according to the users privileges on data   SONY VGP-BPS13A/Q Battery .

Backup and replication

Copies of attributes need to be made regularly in case primary disks or other equipment fails. A periodic copy of attributes may also be created for a distant organization that cannot readily access the original       SONY VGP-BPS13B/Q Battery .

DBMS usually provide utilities to facilitate the process of extracting and disseminating attribute sets. When data is replicated between database servers, so that the information remains consistent throughout the database system and users cannot tell or even know which server in the DBMS they are using, the system is said to exhibit replication transparency   SONY VGP-BPS13B/Q Battery .

Rule enforcement

Often one wants to apply rules to attributes so that the attributes are clean and reliable. For example, we may have a rule that says each car can have only one engine associated with it (identified by Engine Number)     SONY VGP-BPS13/Q Battery .

If somebody tries to associate a second engine with a given car, we want the DBMS to deny such a request and display an error message. However, with changes in the model specification such as, in this example, hybrid gas-electric cars, rules may need to change      SONY VGP-BPS13/Q Battery .

Ideally such rules should be able to be added and removed as needed without significant data layout redesign.

Security

For security reasons, it is desirable to limit who can see or change specific attributes or groups of attributes       SONY VGP-BPS21A/B Battery .

This may be managed directly on an individual basis, or by the assignment of individuals and privileges to groups, or (in the most elaborate models) through the assignment of individuals and groups to roles which are then granted entitlements   SONY VGP-BPS21/S Battery .

Computation

Common computations requested on attributes are counting, summing, averaging, sorting, grouping, cross-referencing, and so on. Rather than have each computer application implement these from scratch, they can rely on the DBMS to supply such calculations  SONY VGP-BPS21B Battery .

Change and access logging

This describes who accessed which attributes, what was changed, and when it was changed. Logging services allow this by keeping a record of access occurrences and changes      SONY VGP-BPS21A Battery .

Automated optimization

For frequently occurring usage patterns or requests, some DBMS can adjust themselves to improve the speed of those interactions. In some cases the DBMS will merely provide tools to monitor performance, allowing a human expert to make the necessary adjustments after reviewing the statistics collected   SONY VGP-BPS21 Battery .

Meta-data repository

Metadata is data describing data. For example, a listing that describes what attributes are allowed to be in data sets is called "meta-information"      Sony VGP-BPS21A/B Battery .

Advanced DBMS

An example of an advanced DBMS is Distributed Data Base Management System (DDBMS), a collection of data which logically belong to the same system but are spread out over the sites of the computer network. The two aspects of a distributed database are distribution and logical correlation        Sony VGP-BPS21/S Battery :

  • Distribution: The fact that the data are not resident at the same site, so that we can distinguish a distributed database from a single, centralized database.
  • Logical Correlation: The fact that the data have some properties which tie them together, so that we can distinguish a distributed database from a set of local databases or files which are resident at different sites of a computer network Sony VGP-BPS21A Battery .

OpenVMS (Open Virtual Memory System ), previously known as VAX-11/VMS, VAX/VMS or (informally) VMS, is a high-end computer serveroperating system that runs on VAX, Alpha and Itanium-based families of computers.Contrary to what its name suggests, OpenVMS is not open source software; however, the source listings are available for purchase  Sony VGP-BPS21 Battery .

Unlike some other mainframe-oriented operating systems, OpenVMS has agraphical user interface (GUI) with complete graphics support. Digital Equipment Corporation's VAX was one of the three top-selling workstations lines in the 1980s and 1990s. VMS had support for professional DTP and CAE software running      Sony Vaio PCG-5G2L Battery .

AXP VMS supported OpenGL and Accelerated Graphics Port (AGP) graphics adapters. It has also been used in education

and for home hobbyist use.

OpenVMS is a multi-user, multiprocessing virtual memory-based operating system (OS) designed for use in time sharing, batch processing, real-time(where process priorities can be set higher than OS kernel jobs), and transaction processing  Sony Vaio PCG-5G3L Battery .

It offers high system availability through clustering, or the ability to distribute the system over multiple physical machines. This allows the system to be "disaster-tolerant" against natural disasters that may disable individual data-processing facilities   Sony Vaio PCG-5J1L Battery .

VMS also includes a process priority system that allows for real-time processes to run unhindered, while user processes get temporary priority "boosts" if necessary.

OpenVMS commercialized many features that are now considered standard requirements for any high-end server operating system  Sony Vaio PCG-5K2L Battery .

These include:

  • Integrated computer networking (originally DECnet and later, TCP/IP)
  • Symmetrical, asymmetrical, and NUMA multiprocessing, including clustering
  • A distributed file system (Files-11)      Sony Vaio PCG-5J2L Battery
  • Integrated database features such as RMS and layered databases including Rdb
  • Support for multiple computer programming languages
  • A standardized interoperability mechanism for calls between different programming languages
  • An extensible shell command language (DIGITAL Command Language)  Sony Vaio PCG-5K1L Battery
  • Hardware partitioning of multiprocessors
  • High level of security  Sony Vaio PCG-5L1L Battery

Enterprise-class environments typically select and use OpenVMS for various purposes including as a mail server, network services, manufacturing or transportation control and monitoring, critical applications and databases, and particularly environments where system uptime and data access is critical     Sony Vaio PCG-6S2L Battery .

System up-times of a decade or more have been reported, and features such as Rolling Upgrades and clustering allow clustered applications and data to remain continuously accessible while operating system software and hardware maintenance and upgrades are performed, or when a whole data center is destroyed        Sony Vaio PCG-6S3L Battery .

Customers using OpenVMS include banks and financial services, hospitals and healthcare, network information services, and large-scale industrial manufacturers of various products.

In April 1975, Digital Equipment Corporation embarked on a hardware project, code named Star, to design a 32-bit virtual address extension to its PDP-11 computer line         Sony Vaio PCG-6V1L Battery .

A companion software project, code named Starlet, was begun in June 1975 to develop a totally new operating system, based onRSX-11M, for the Star family of processors. These two projects were tightly integrated from the beginning. Gordon Bell was the VP lead on the VAX hardware and its architecture     Sony Vaio PCG-6W1L Battery .

Roger Gourd was the project lead for the Starlet program, with software engineers Dave Cutler (who would later lead development of Microsoft's Windows NT), Dick Hustvedt, and Peter Lippman acting as the technical project leaders, each having responsibility for a different area of the operating system        Sony Vaio PCG-6W2L Battery .

The Star and Starlet projects culminated in the VAX 11/780 computer and the VAX-11/VMS operating system. The Starlet name survived in VMS as a name of several of the main system libraries, including STARLET.OLB and STARLET.MLB.

Over the years the name of the product has changed. In 1980 it was renamed, with version 2.0 release, to VAX/VMS (at the same time as the VAX-11 computer was renamed to simply VAX)      Sony Vaio PCG-6W3L Battery .

With the introduction of the MicroVAX range such as the MicroVAX I, MicroVAX II and MicroVAX 2000 in the mid-to-late 1980s, DIGITAL released MicroVMS versions specifically targeted for these platforms which had much more limited memory and disk capacity      Sony Vaio PCG-7111L Battery ;

e.g. the smallest MicroVAX 2000 had a 40MB RD32 hard disk and a maximum of 6MB of RAM, and its CPU had to emulate some of the VAX floating point instructions in software. MicroVMS kits were released for VAX/VMS 4.4 to 4.7 on TK50 tapes and RX50 floppy disks, but discontinued with VAX/VMS 5.0        Sony Vaio PCG-7112L Battery .

In 1991 it was renamed again to OpenVMS to indicate its support for industry standards such as POSIX and Unix compatibility, and to drop the hardware connection as the port to DIGITAL's 64-bit Alpha RISC processor was in process. The OpenVMS name first appeared after the version 5.4-2 release        Sony Vaio PCG-7113L Battery .

Port to DEC Alpha

The VMS port to Alpha resulted in the creation of a second and separate source code libraries (based on a source code management tool known as VDE) for the VAX 32-bit source code library and a second and new source code library for the Alpha (and the subsequent Itanium port) 64-bit architectures        Sony Vaio PCG-7133L Battery .

1992 saw the release of the first version of OpenVMS for Alpha AXP systems, designatedOpenVMS AXP V1.0. The decision to use the 1.x version numbering stream for the pre-production quality releases of OpenVMS AXP caused confusion for some customers and was not repeated in the next platform port to the Itanium       Sony Vaio PCG-7Z2L Battery .

In 1994, with the release of OpenVMS version 6.1, feature (and version number) parity between the VAX and Alpha variants was achieved. This was the so-called Functional Equivalence  release, in the marketing materials of the time. Some features were missing however, e.g. based shareable images, which were implemented in later versions     Sony Vaio PCG-8Y1L Battery .

Subsequent version numberings for the VAX and Alpha variants of the product have remained consistent through V7.3, though Alpha subsequently diverged with the availability of the V8.2 and V8.3 releases.

For general details on the port to Alpha, see the OpenVMS 20th Anniversary book     Sony Vaio PCG-8Y2L Battery .

For technical details on the port, see the DIGITAL Technical Journal Volume 4 Number 4.

Port to Intel Itanium

In 2001, just prior to its acquisition by Hewlett-Packard, Compaq announced the port of OpenVMS to the Intel Itanium architecture  Sony Vaio PCG-8Z1L Battery .

This port was accomplished using source code maintained in common within the OpenVMS Alpha source code library, with conditional and additional modules where changes specific to Itanium were required      Sony Vaio PCG-8Z2L Battery .

The OpenVMS Alpha pool was chosen as the basis of the port as it was significantly more portable than the original OpenVMS VAX source code, and because the Alpha source code pool was already fully 64-bit capable (unlike the VAX source code pool)  Sony VAIO PCG-5G2L Battery .

With the Alpha port, many of the VAX hardware-specific dependencies had been previously moved into the Alpha SRM firmware for OpenVMS. Features necessary for OpenVMS were then moved from SRM into OpenVMS I64 as part of the Itanium port  Sony VAIO PCG-5G3L Battery .

Unlike the port from VAX to Alpha, in which a snapshot of the VAX code base circa V5.4-2  was used as the basis for the Alpha release and the 64-bit source code pool then diverged, the OpenVMS Alpha and I64 (Itanium) versions of OpenVMS are built and maintained using a common source code library and common tools      Sony VAIO PCG-5J1L Battery .

The core software source code control system used for OpenVMS is the VMS Development Environment (VDE); see the VDE installation kit for details.

Two pre-production releases, OpenVMS I64 V8.0 and V8.1, were available on June 30, 2003 and on December 18, 2003  Sony VAIO PCG-5K2L Battery .

These releases were intended for HP organizations and third-party vendors involved with porting software packages to OpenVMS I64.

The following are recent OpenVMS I64 releases:

OpenVMS I64 V8.2, the first production-quality Itanium release, was shipped January 13, 2005     Sony VAIO PCG-5J2L Battery .

A V8.2 release is also available for Alpha platforms.

OpenVMS I64 V8.2-1, adding support for Integrity Superdome and cell based systems, was released in September 2005. V8.2-1 is available for Itanium platforms only.

OpenVMS I64 V8.3, was released for Itanium platforms in September 2006. V8.3 is also available for Alpha systems  Sony VAIO PCG-5K1L Battery .

OpenVMS I64 V8.3-1H1, was released in October 2007. It features full c-Class Integrity BladeServer blade support. See the full announcement for details.HP BladeSystem information for details onblade server products from HP.

OpenVMS I64 and Alpha V8.4, was released in June 2010. See the OpenVMS V8.4 release announcement for details  Sony VAIO PCG-5L1L Battery .

For technical details on the OpenVMS port to Itanium, see the OpenVMS Technical Journal V6. In particular, see the Porting OpenVMS to Integrity article. Information on OpenVMS releases from V4.0 to current is available, as are listings of upgrade paths in the OpenVMS FAQ and at the HP OpenVMS site   Sony VAIO PCG-6S2L Battery .

Graphical user interface

OpenVMS uses the DECwindows Motif user interface (based on CDE) layered on top of OpenVMS's X11 compliant windowing system.

Clustering

OpenVMS supports clustering (first called VAXcluster and later VMScluster), where multiple systems share disk storage, processing, job queues and print queues, and are connected either by specialized hardware or an industry-standard LAN (usually Ethernet)  Sony VAIO PCG-6S3L Battery .

A LAN-based cluster is often called a LAVc, for Local Area Network VMScluster, and allows, among other things, bootstrapping a possibly diskless satellite node over the network using the system disk of a bootnode.

VAXcluster support was first added in VMS version 4, which was released in 1984        Sony VAIO PCG-6V1L Battery .

This version only supported clustering over CI. Later releases of version 4 supported clustering over LAN (LAVC), and support for LAVC was improved in VMS version 5, released in 1988.

Mixtures of cluster interconnects and technologies are permitted, including Gigabit (GbE) Ethernet, SCSI, FDDI, DSSI, CI and Memory Channel adapters      Sony VAIO PCG-6W1L Battery .

OpenVMS supports up to 96 nodes in a single cluster, and allows mixed-architecture clusters, where VAX and Alpha systems, or Alpha and Itanium systems can co-exist in a single cluster (Various organizations have demonstrated triple-architecture clusters and cluster configurations with up to 150 nodes, but these configurations are not supported by HP)       Sony VAIO PCG-6W2L Battery .

Unlike many other clustering solutions, VAXcluster offers transparent and fully distributed read-write with record-level locking, which means that the same disk and even the same file can be accessed by several cluster nodes at once; the locking occurs only at the level of a single record of a file, which would usually be one line of text or a single record in a database   Sony VAIO PCG-6W3L Battery .

This allows the construction of high-availability multiply redundant database servers.

Cluster interconnections can span upwards of 500 miles, allowing member nodes to be located in different buildings on an office campus, or in different cities   Sony VAIO PCG-7111L Battery .

Host-based volume shadowing allows volumes (of the same or of different sizes) to be shadowed (mirrored) across multiple controllers and multiple hosts, allowing the construction of disaster-tolerant environments      Sony VAIO PCG-7112L Battery .

Full access into the distributed lock manager (DLM) is available to application programmers, and this allows applications to coordinate arbitrary resources and activities across all cluster nodes. This obviously includes file-level coordination, but the resources and activities and operations that can be coordinated with the DLM are completely arbitrary  Sony VAIO PCG-7113L Battery .

With the supported capability of rolling upgrades and with multiple system disks, cluster configurations can be maintained on-line and upgraded incrementally. This allows cluster configurations to continue to provide application and data access while a subset of the member nodes are upgraded to newer software versions  Sony VAIO PCG-7Z1L Battery .

For general details, see the OpenVMS Cluster SPD. For more specific details, see the clustering-related manuals in the OpenVMS documentation set.

File system

OpenVMS has a very feature-rich file system, with support for stream and record-oriented IO, ACLs, and file versioning. The typical user and application interface into the file system is the RMS     Sony VAIO PCG-7Z2L Battery .

Details are in the RMS Util

ities and RMS programming manuals, and in the I/O User's Reference Manual, all part of the OpenVMS documentation set. Also see the available ODS2 documentation, and the VMS File Systems Internals book, by Kirby McCoy, ISBN 1-55558-056-4     Sony VAIO PCG-8Y1L Battery .

Timekeeping

OpenVMS represents system time as the 64-bit number of 100 nanosecond intervals (that is, ten million units per second; also known as a 'clunk' ) since the epoch. The epoch of OpenVMS is midnight preceding November 17, 1858, which is the start of Modified Julian Day numbering       WD passport essential (500GB/640GB) .

The clock is not necessarily updated every 100 ns; for example, systems with a 100 Hz interval timer simply add 100 000 to the value every hundredth of a second. The operating system includes a mechanism to adjust for hardware timekeeping drift; when calibrated against a known time standard, it easily achieves an accuracy better than 0.01%  WD passport essential (250GB/320GB) .

All OpenVMS hardware platforms derive timekeeping from an internal clock not associated with the AC supply power frequency.

While the system is shut down, time is kept by a Time-of-Year ("TOY") hardware clock. This clock keeps time to a lower resolution (perhaps 1 second) and generally, a lower accuracy (often 0.025% versus 0.01%)   WD  passport essential SE (750GB/1TB .

When the system is restarted, the VMS 64-bit time value is recomputed based on the time kept by the TOY clock and the last recorded year (stored on the system disk).

The 100 nanosecond granularity implemented within OpenVMS and the 63-bit absolute time representation   WD  passport elite(250GB/320GB)

(the sign bit indicates absolute time when clear and relative time when set) should allow OpenVMS trouble-free time computations up to 31-JUL-31086 02:48:05.47. At this instant, all clocks and time-keeping operations in OpenVMS will suddenly fail, since the counter will overflow and start from zero again    WD passport elite(500GB/640GB) .

Though the native OpenVMS time format can range far into the future, applications based on the C runtime library will likely encounter timekeeping problems beyond January 19, 2038 due to the Year 2038 problem. Many components and applications may also encounter field-length-related date problems at year 10000 (see the Year 10,000 problem)  WD  passport studio for Mac(320GB/500GB) .

Detailed information on time and timekeeping, and on daylight saving time and timezone differential factor operations, is contained in the OpenVMS FAQ.

Programming

The common language programming environment is described in the OpenVMS Calling Standard and the OpenVMS Programming Concepts manuals       WD  passport studio for Mac(500GB/640GB) .

This provides mixed-language calls, and a set of language-specific, run-time library (RTL), and system service routines. The language calls and the RTLs are implemented in user-mode shareable images, while the system services calls are generally part of the operating system, or part of privileged-mode code        WD  Elements series(250GB/320GB) .

This distinction between languages and RTLs and system services was once fairly clean and clear, but the implementations and specifics have become rather more murky over the years.

Various utilities and tools are integrated, as are various add-on languages and tools      WD  Elements SE(500GB/640GB) .

Many Programming Examples are available, see the pointers in the OpenVMS FAQ.

Debugging

The VMS Debugger supports all DEC compilers and many third party languages. It allows breakpoints, watchpoints and interactive runtime program debugging either using a command line or graphicaluser interface. OpenVMS Debugger Manual WD Elements SE(750GB/1TB)

Common Language Environment

Among OpenVMS's notable features is the Common Language Environment, a strictly defined standard that specifies calling convention for functions and routines, including use of stacks, registers, etc., independently of programming language  WD  Elements desktop(500GB/640GB) .

Because of this, it is possible to call a routine written in one language (e.g. Fortran) from another (e.g. COBOL), without needing to know the implementation details of the target language. OpenVMS itself is implemented in a variety of different languages (primarily BLISS, VAX Macro and C)        WD  Elements desktop(750GB/1TB)

(per comp.os.vms newsgroup postings from members of HP OpenVMS Engineering), and the common language environment and calling standard supports freely mixing these languages, and Ada, PL/I, Fortran, BASIC, and others. This is in contrast to a system such as Unix, which is implemented nearly entirely in the C language       WD  Elements desktop(1.5 TB/2TB) .

For details on these compilers and libraries, see the language manuals available at OpenVMS documentation.

Macro32 (an assembler on OpenVMS VAX, and a compiler on OpenVMS Alpha and on OpenVMS I64) is available within and integrated into OpenVMS        WD  passport essential SE (750GB/1TB)--USB 3.0)      .

BLISS compilers are available for download from the OpenVMS Freeware, as are various ports of Perl, PHP, Ruby and other languages. Java is available from the HP Java website. C, Fortran and other languages are commercial products, and are available for purchase         WD  passport essential (500GB/640GB) .

Run-time Libraries

OpenVMS contains a very rich set of Run-time Libraries (RTLs). These cover a wide range of functions, including String manipulation (STR$ routines), Mathematical operations (MTH$ routines), the Run-time Library (LIB$) routines       WD  passport for Mac(320GB/500GB) ,

Screen Management operations (SMG$ routines) and a number of other categories grouped together as General Purpose functions (OTS$ routines). These functions, combined with the low-level System Services, make it easy to write complex programs      WD  passport for Mac(640GB/1TB) .

Before writing a simple program in a high-level programming language, however, users should consider if the needed operation can be performed using DCL's functions from a command file. Start with the OpenVMS User's Guide. For details on the programming interfaces, see the associated manuals in the OpenVMS documentation        My book essential 4 generation  (640GB/1TB) .

Security

OpenVMS provides various security features and mechanisms, including security identifiers, resource identifiers, subsystem identifiers, ACLs, and detailed security auditing and alarms         WD  My book essential 4 generation( 1.5TB/2TB) .

Specific versions evaluated at DoD NCSC Class C2 and, with the SEVMS security enhanced services support, at NCSC Class B1, per the NCSC Rainbow Series. OpenVMS also holds an ITSEC E3 rating. For details on these ratings and the specific associated OpenVMS versions and ratings, see the NCSC and Common Criteria pages, and the associated product listings  WD  My book elite( 1TB/1.5TB) .

For details on the OpenVMS security mechanisms, see the HP OpenVMS Guide to System Security manual available at the OpenVMS documentation web site. Also see the OpenVMS securityinformation   WD  My book studio(1TB/2TB) .

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