• Older architectures were, like modern enterprise architectures, built using a client server model. However unlike modern enterprise architectures the server side was not seperated into layers / tiers.
  • The presentation, processing, data retrieval/update (and sometimes data storage) was all wrapped up in a single monolithic application/ code module.
  • This led to serious problems:
  • It was not re-useable
    • As the processing, presentation and data access is tied together it was difficult to spit out and reuse part so the code without heavy rewriting / restructuring.
  • It did not handle scaling well.:
    • Increased data – As the data storage and access is tied in with the logic and presentation parts of the application you cannot move it onto a different machine to handle the extra data.
    • Increased load – You cannot split out the presentation, processing and data storage/access to run on separate machines so as to reduce the load on each.
    • Increased modules / processes – Creating new modules can require duplication of the data access and presentation code as they are not seperate from the rest of the application.
  • The Solution: N – tier architectures:
    • Application is broken into separate tiers, each of which performs a different function
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