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This page describes content that exists only in outdated versions of Java Edition. 
The format only exists in inf-20100624, and was promptly scrapped and reverted back to the Alpha level format when inf-20100625-1 was released.
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A new save format was introduced in Java Edition Infdev 20100624, changing from the Alpha level format used previously. However, this new save format made world files morbidly larger than those with the Alpha level format, and as such its use was resumed in the version immediately after.

Every 5 to 10 seconds or so, your world size will increase in nearly 200 MB in size.

Folder structure[]

In the "Worldn" folder, a "data" folder existed, containing .dat files for storing blocks ("zone") and entities ("entities"), with the groups of chunks seemingly labelled with hexadecimal numbers. It is in Base36.