The .txt file extension is one of the most ubiquitous file types. The file generally consists of plain text only and contains no formatting. Almost any application that can handle text can open a .txt file. As a result this format remains popular due to its support across all platforms and Operating Systems. The file type is one of the oldest file types in existence with its origins tracing back to the first computers.
A .txt file normally uses a basic character set which contains letters, numbers and symbols. A typical example of this would be the ASCII character set. The main alternative to ASCII is Unicode. Unicode is a rival format for text files. A plain text file should only contain several non-printable charaters such as new lines, tab and form feed.
MP3 is a digital music format which allows CD tracks to be reduced to around a tenth of their normal size without a significant loss of quality. MP3 gets rid of a lot of the information recorded in a song that our ears are not able to hear and then uses complex algorithms to reduce the file size. This then enables you to get hundreds of songs on to a CD and it also has opened up a new market over the internet - the download market as download times have been significantly reduced.
The MP3 format is a lossy format. That means that an MP3 file does not contain 100% of the original audio information. Instead, MP3 files use perceptual coding. In other words, that means it removes the information that your ear doesn't notice thereby making the file smaller. The reason lossy formats are used over RAW is that RAW audio files are too large to travel over the internet at any great speed. By using lossy formats it enables even dial up users to download mp3 files at a reasonable speed. RAW file formats generally require 176,000 bytes per second compared to a lossy format which requires 17,600. The difference is massive and so are the download times.