Legacy technologies are mostly tied to a specific version of an OS or coding language. I.e. some apps/programs may be available for Android 5 (Windows 7) but won't be for Android 10 (Windows 10).
A big example of discontinued support is Microsoft's Internet Explorer. At the start of 2016 Microsoft ended support for all versions of IE.
Even small changes to a legacy system may result in slower performance, higher resource consumption and more frequent failures and crashes. Additionally legacy apps cannot adhere to modern safety and security standards.
- Deprecated Code/Technology
Deprecation, in its programming sense, is the process of taking older code and marking it as no longer being useful within the codebase, usually because it has been superseded by newer code.
The deprecated code is not immediately removed from the codebase because doing so may cause regression errors.
There are many articles available online on this topic.