Film is rearranged metal particles on tape which are read by an electromagnet. CDs are discs with burned pits in them which are read by a laser. What makes one analog and one digital?
In: Technology
You are confusing film with tape. Film is read by shining a light through it while a tape is read by an electromagnet. The difference between analog and digital is how many different levels the signal can have in its raw format. In an analog format there is no limit to the granularity of the data other then those imposed by the material. For example a film can be fully transparent to completely opaque and everything in between. However the raw format on a CD is either fully flat or a full depth grove. There is no half way in between. The problem is that the laser in the CD is not arranged in such a way that it can pick up more then two levels. However if you for example were able to get a needle to read the depth of the groves you could store analog data in the same format, this is what vinyl records did. It is the analog version of a CD. Similarly there are digital formats of tapes as well, firstly the Digital Audio Cassette which were a consumer grade product but it is the same technology behind the tape as in hard drives and those are digital. Tapes is also very popular for enterprise systems for huge amounts of storage because it is the cheapest form of data storage.
The advantage of storing things in a digital format is that the data is there even if there is some change in the medium which cause its signal level to change. You know there are only two valid signal levels so if you get something in between you can just round it to the closest valid level and you have not lost any data. This means you can have a lot of signal interference without losing any of the data.
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