They are often stored in compressed form . Just as images can be compressed to save storage space, so too can numerical data. They must be expanded into their original ascii text form to be used. The cm98.zip is a case in point. When expanded, it may be 5-6 times as big.
Compression is used to reduce storage stace and speed modem downloads.
They are occasionally formatted for a particular analysis software . Over the years, certain software has assumed major popularity and thus data often are ordered specially for it. Fortunately, most analysis software can translate one format into another. Some generic forms exist such as tab delimited , space delimited , and comma delimited . Choose one of these if available and an exact format match to your analysis software isn't.