buildings and plants are used for 50+ years, but computer programs ( and storage media) have a half life of about 5 yrs. Not only do the programs become obsolete, but the companies that service the program also disappear .
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davefitz, you hit the point! In the company I worked for last 15 years we changed from AutoCAD v.9 to 2002. We have projects stored on 5,25 inch diskettes, on 120 MB (Huge size!!!) strimmer cassetes, on CD's. How can one open now something stored somewhere on first two media types?
5,25 floppy drives are not more produced, strimmer cassette drive is saved somewhere in the storage, but it needs DOS drivers (now floppy disk with these drivers is missing) - so these archives can be considered lost. And this is situation inside the company!
Now I must evaluate and update a project where original design is made 10 years ago y another company using "Microstation" software. I have original files, but only in "Microstation" format. Only hardcopies help me to find what is installed in the control panels. And I have two options - either to find somebody who still uses Microstation and to ask him to convert files in .dxf, either totally redraw paper copies!
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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant