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The notion of sparse file, and the ways of handling it from the point of view of GNU tar user have been described in detail in sparse. This chapter describes the internal format GNU tar uses to store such files.
The support for sparse files in GNU tar has a long history. The earliest version featuring this support that I was able to find was 1.09, released in November, 1990. The format introduced back then is called old GNU sparse format and in spite of the fact that its design contained many flaws, it was the only format GNU tar supported until version 1.14 (May, 2004), which introduced initial support for sparse archives in PAX archives (see posix). This format was not free from design flows, either and it was subsequently improved in versions 1.15.2 (November, 2005) and 1.15.92 (June, 2006).
In addition to GNU sparse format, GNU tar is able to read and extract sparse files archived by star.
The following subsections describe each format in detail.