digital data is preserved by archiving on a removable medium . in the long term , the save data bit stream must be correctly interpreted . for a computer program or system to be archived , the bit stream constituting the program must be archived and the code must be executable at restore time . the program that restores the data does not “ see ” the contents of the data itself , but accesses it by issuing a function call to an executor . a description of which methods are available to restore the information hidden in the data is always available . a text tells the client which functions are available and what their purposes are . the archiving method is based on using a virtual computer instruction set and saving the algorithm as a program written int hat virtual machine language . for machine instructions to be executed many years later , for example 100 years , an emulator of the original machine would be written on the future hardware . any machine manufactured in the originating year would develop for each architecture a universal virtual computer description of the machine . each originating instruction would be mapped into a small program of uvc instructions . all manufacturers of new architectures would then have to write a uvc executor which would be able to execute uvc instructions on the machine running 100 years in the future .