Legacy system

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System Fundamentals[1]

In computing, a legacy system is an old method, technology, computer system, or application program, "of, relating to, or being a previous or outdated computer system."Often a pejorative term, referencing a system as "legacy" often implies that the system is out of date or in need of replacement.[2]

Legacy systems are usually still in use as opposed to retired (or archived) systems, which are no longer in use. Please remember this distinction.

All about legacy systems

Systems must be compatibleA state in which two things are able to exist or occur together without problems or conflict. with other systems if they are going to be useful. Legacy systems are not always compatibleA state in which two things are able to exist or occur together without problems or conflict. with newer systems. CompatibilityA state in which two things are able to exist or occur together without problems or conflict. is a stateGive a specific name, value or other brief answer without explanation or calculation. in which two things are able to exist or occur together without problems or conflict. When you are planning a new system, you should be aware of compatibilityA state in which two things are able to exist or occur together without problems or conflict. issues with older systems. Frequently, the way a legacy system stores data is the most frequent source of compatibilityA state in which two things are able to exist or occur together without problems or conflict. issues. Please also understand the range of possible problems legacy systems can have:

  1. Maintaining old systems often includes old application programs
  2. Legacy systems can be hard to understand and expensive to change because programs might be disorganized
  3. Documentation might be missing
  4. Poor maintenance might introduce security problems
  5. It may be difficult to find people who have the knowledge and skills to work with old systems
  6. Legacy system are typically quite large and complex


A few hypothetical examples may help you understand this:

  1. A new system accepts input for a date as 11 November 2017, but the legacy system only accept input as 11 November 17
  2. A new system is web-based, but an older system is not web-based
  3. A new system allows UTF-8 (Unicode Transformation Format-8) characters but the legacy system does not.
  4. A new system assumes all currencies are in US dollars, while the legacy system does not.
  5. A new system stores time as HH:MM:SS:MS (HH: hour, MM: minute, SS: second, MS: millisecond) but the legacy system stores time as HH:MM:SS.
  6. A new system assumes all numbers can have 4 decimal places, while a legacy system assumes all numbers only have 2 decimal places.
  7. A new system stores data in XML while a legacy system stores data in plain text.

Real-world practical advice

When you are planning a new system you should include compatibilityA state in which two things are able to exist or occur together without problems or conflict. planning as part of your new system. If you are a system administrator, programmer, networka group or system of interconnected people or things. administrator, much of your work will involve getting different systems to be compatibleA state in which two things are able to exist or occur together without problems or conflict.. It's always nice when you have a new system, new company, and a new process, but this isn't the norm.

There is a lot more to say about this, but my advice is to assume any system you are involved with needs to be compatibleA state in which two things are able to exist or occur together without problems or conflict. with other systems and legacy systems.

Standards

  • OutlineGive a brief account. compatibilityA state in which two things are able to exist or occur together without problems or conflict. issues resulting from situations including legacy systems or business mergers.

References