Legacy system

A legacy system is an old computer system or application program that continues to be used because the user (typically an organization) does not want to replace or redesign it. A computer is a Machine that manipulates data according to a list of instructions. Application software is a subclass of Computer software that employs the capabilities of a computer directly and thoroughly to a task that the user wishes to perform

1 Overview
2 Legacy support
3 Brownfield architecture
4 Alternative view
5 See also
6 References
7 Further reading

Overview

Legacy systems are considered to be potentially problematic by many software engineers (for example, see Bisbal et al. , 1999) for several reasons. Legacy systems often run on obsolete (and usually slow) hardware, and sometimes spare parts for such computers become increasingly difficult to obtain. These systems are often hard to maintain, improve, and expand because there is a general lack of understanding of the system. The designers of the system may have left the organization, leaving no one left to explain how it works. Such a lack of understanding can be exacerbated by inadequate documentation or manuals getting lost over the years. Integration with newer systems may also be difficult because new software may use completely different technologies.

Despite these problems, organizations can have compelling reasons for keeping a legacy system, such as:

The costs of redesigning the system are prohibitive because it is large, monolithic, and/or complex. A monolithic architecture is where processing data and the user interface all reside on the same system.
The system requires close to 100% availability, so it cannot be taken out of service, and the cost of designing a new system with a similar availability level is high. In Telecommunications and Reliability theory, the term availability has the following meanings 1
The way the system works is not well understood. Such a situation can occur when the designers of the system have left the organization, and the system has either not been fully documented or such documentation has been lost.
The user expects that the system can easily be replaced when this becomes necessary.
The system works satisfactorily, and the owner sees no reason for changing it; or in other words, re-learning a new system would have a prohibitive attendant cost in lost time and money.

If legacy software runs on only antiquated hardware, the cost of maintaining the system may eventually outweigh the cost of replacing both the software and hardware unless some form of emulation or backward compatibility allows the software to run on new hardware. Typical PC hardware A typical Personal computer consists of a case or chassis in a tower shape (desktop and the following parts Motherboard An emulator duplicates (provides an emulation of the functions of one System using a different system so that the second system behaves like (and appears to In Technology, especially Computing (irrespective of platform a product is said to be backward compatible when it is able to take the place of an older product However, many of these systems do still meet the basic needs of the organization. The systems to handle customers' accounts in banks are one example. A banker or bank is a Financial institution whose primary activity is to act as a payment agent for customers and to borrow and lend money Therefore the organization cannot afford to stop them and yet some cannot afford to update them.

A demand of extremely high availability is commonly the case in computer reservation systems, air traffic control, energy distribution (power grids), nuclear power plants, military defense installations, and other systems critical to safety, security, traffic throughput, and/or economic profits. A computer reservations system ( CRS) is a Computerized system used to store and retrieve information and conduct transactions related to Air travel. Air traffic control ( ATC) is a service provided by ground-based controllers who direct Aircraft on the ground and in the air Electric power transmission, a process in the delivery of Electricity to consumers is the bulk transfer of electrical power Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions For example see the TOPS database system. Total Operations Processing System, or TOPS, is a computer system for managing the Locomotives and Rolling stock ( Railroad cars owned by

The change being undertaken in some organizations is to switch to Automated Business Process (ABP) software which generates complete systems. Many computer systems are available in the commercial marketplace that address the various aspects of Business Process Management. These systems can then interface to the organizations' legacy systems and use them as data repositories. A repository is a place where Data or specimens are stored and maintained for future retrieval This approach can provide a number of significant benefits: the users are insulated from the inefficiencies of their legacy systems, and the changes can be incorporated quickly and easily in the ABP software. (At least, that's the intention. )

Note that "legacy" has little to do with the size or even age of the system — mainframes run 64-bit Linux and Java, after all, right alongside 1960s vintage code. Mainframes (often colloquially referred to as Big Iron) are Computers used mainly by large organizations for critical applications typically bulk data Linux (commonly pronounced ˈlɪnəks In fact, some of the thorniest legacy problems organisations now face are in trying to leverage or replace existing "fat client" Visual Basic code as customers demand reliable Web access. A fat client or rich client is a computer ( client) in Client-server architecture networks which typically provides rich functionality independently Visual Basic ( VB) is the third-generation event-driven programming language and associated development environment (IDE from

Legacy support

The term legacy support is often used with reference to obsolete or "legacy" computer hardware, whether peripherals or core components. For an account of the words periphery and peripheral as they are used in biology sociology politics computer hardware and other fields see the Operating systems with "legacy support" can detect and use legacy hardware. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination

It is also used as a verb for what vendors do for products in legacy mode - they "support", or provide software maintenance, for obsolete or "legacy" products. In Software engineering, software maintenance is the modification of a software product after delivery to correct faults to improve performance or other attributes or to adapt

In some cases, "legacy mode" refers more specifically to backward compatibility. In Technology, especially Computing (irrespective of platform a product is said to be backward compatible when it is able to take the place of an older product

The computer mainframe era saw many applications running in legacy mode. Mainframes (often colloquially referred to as Big Iron) are Computers used mainly by large organizations for critical applications typically bulk data In the modern business computing environment, n-tier, or 3-tier architectures are more difficult to place into legacy mode as they include many components making up a single system. In Software engineering, multi-tier architecture (often referred to as n-tier architecture) is a Client-server architecture in which an application In Software engineering, multi-tier architecture (often referred to as n-tier architecture) is a Client-server architecture in which an application The term architecture (from Greek αρχιτεκτονικήarchitektoniki) can be used to mean a process a profession or documentation Government regulatory changes must also be considered in a system running in legacy mode.

Virtualization technology allows for a resurgence of modern software applications entering legacy mode. Application software is a subclass of Computer software that employs the capabilities of a computer directly and thoroughly to a task that the user wishes to perform As system complexity and software costs increase, many computing users are keeping their current systems permanently in legacy mode.

Brownfield architecture

IT has borrowed the term brownfield from the building industry, where undeveloped land (and especially unpolluted land) is described as greenfield and previously developed land – which is often polluted and abandoned – is described as brownfield. ^[1]

A brownfield architecture is an IT network design that incorporates legacy systems.
A brownfield deployment is an upgrade or addition to an existing IT network and uses some legacy components.

Alternative view

There is an alternate point of view — growing since the "Dot Com" bubble burst in 1999 — that legacy systems are simply (and only) computer systems that are both installed and working. Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar) In other words, the term is not at all pejorative — quite the opposite. Perhaps the term "legacy" is only an effort by computer industry salesmen to generate artificial churn in order to encourage purchase of unneeded technology. Bjarne Stroustrup, creator of the C++ language, addressed this issue succinctly:

"Legacy code" often differs from its suggested alternative by actually working and scaling. Bjarne Stroustrup (/'bjɑːnə 'sdʁʌʊ̯ˀsdʁɔb/ born December 30, 1950 in Aarhus C++ (" C Plus Plus " ˌsiːˌplʌsˈplʌs is a general-purpose Programming language.

—Bjarne Stroustrup

IT analysts estimate that the cost to replace business logic is about five times that of reuse, and that's not counting the risks involved in wholesale replacement. Shareholders and managers are increasingly asking, "Why are we spending so much money on new technology with so little to show for it?" Ideally businesses would never have to rewrite most core business logic. A rewrite in Computer programming is the act or result of re-implementing a large portion of existing functionality without re-use of its Source code. After all, debits must equal credits — they always have, and they always will. Businesses and governments are also recoiling at well-publicized system failures and security breaches that all too commonly arrive with new software — failures which are utterly catastrophic in many cases. (A regional airline fired its CEO due to the failure of an antiquated legacy crew scheduling system during Christmas, 2004, for example. Regional airlines commonly called commuter airlines or feeder airlines, when they provide service to smaller communities that do not generate sufficient passengers "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " ^[2]) There's also a growing backlash against large, packaged software products (SAP, Oracle, PeopleSoft, and others) which were oversold and in some cases have proven too costly, inflexible, and poorly matched to business needs. SAP AG (,) is the largest European Software enterprise and the fourth largest in the world with headquarters in Walldorf, Germany Oracle Corporation ( specializes in developing and marketing Enterprise software products — particularly Database management systems In 2007 Oracle ranked PeopleSoft Inc was a company that provided Human resource management systems (HRMS Customer relationship management, Manufacturing Financials Enterprise

Increasingly the IT industry is responding to these understandable business concerns. "Legacy modernization" and "legacy transformation" are now popular terms, and they mean reusing and refactoring existing, core business logic by providing new user interfaces (typically Web interfaces) sometimes through the use of techniques such as screen scraping and service-enabled access (e. Screen scraping is a technique in which a Computer program extracts Data from the display Output of another program g. , through Web services). A Web service (also Web Service) is defined by the W3C as "a software system designed to support interoperable machine-to-machine interaction These techniques allow organisations to understand their existing code assets (using discovery tools), provide new user and application interfaces to existing code, improve workflow, contain costs, minimize risk, and enjoy classic qualities of service (near 100% uptime, security, scalability, etc. ). Technology companies involved in "enterprise transformation" are growing and profiting by what many people feel is a more rational approach toward legacy systems.

The reexamination of attitudes toward legacy systems is also inviting more reflection on what makes legacy systems as durable as they are. Technologists are relearning the fact that sound architecture, practiced up front, helps businesses avoid costly and risky rewrites in the first place. In Computer engineering, computer architecture is the conceptual design and fundamental operational structure of a Computer system The most common legacy systems tend to be those which embraced well-known IT architectural principles, with careful planning and strict methodology during implementation. Poorly designed systems often don't last. Thus, many organisations are rediscovering not only the value in the legacy systems themselves but also their philosophical underpinnings.

References

Dictionary

-noun

(computing) An old computer system or application program that continues to be used because the user (typically an organization) does not want to replace or redesign it.

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