# Why is the 13th charcater always a 4?

**URL:** <https://forum.duplicati.com/t/why-is-the-13th-charcater-always-a-4/6843>\
**Category:** Support\
**Created:** [April 16, 2019, 10:44am UTC](https://forum.duplicati.com/t/why-is-the-13th-charcater-always-a-4/6843 "2019-04-16T10:44:14Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![kees-z](https://forum.duplicati.com/user_avatar/forum.duplicati.com/kees-z/32/29_2.png) [@kees-z](https://forum.duplicati.com/u/kees-z)\
**Post date:** [April 16, 2019, 10:44am UTC](https://forum.duplicati.com/t/why-is-the-13th-charcater-always-a-4/6843/1 "2019-04-16T10:44:14Z")

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I noticed something odd regarding backend filenames.

I was assuming that filenames were completely random except for the prefix and extension, but it appears that the 13th “random” character of **every** DBLOCK and DINDEX file is always a 4!

This does not seem to be limited to any Duplicati version (DBLOCK and DINDEX files created years ago as well as recent ones have a 4 at pos.13).  
There’s also no difference between used backends: in OneDrive, Local storage, WebDAV backends there’s a 4 at position 13 of every DINDEX and DBLOCK file.

Can anyone explain why this is happening?

![image](https://forum.duplicati.com/uploads/default/original/2X/a/a7fd60268798e5f16435cbac22e6a5c8553785e3.png)

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**Author:** ![nescafe](https://forum.duplicati.com/user_avatar/forum.duplicati.com/nescafe/32/2050_2.png) [@nescafe](https://forum.duplicati.com/u/nescafe)\
**Post date:** [April 16, 2019, 2:06pm UTC](https://forum.duplicati.com/t/why-is-the-13th-charcater-always-a-4/6843/2 "2019-04-16T14:06:02Z")

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This is a GUID, you can read the answer on SO: [SQL Server : why is the 15th char of a GUID always 4? - Stack Overflow](https://stackoverflow.com/questions/9332649/sql-server-why-is-the-15th-char-of-a-guid-always-4)

(15th position =\> 13th position due to removal of dashes)

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<div class="post-metadata">

**Author:** ![kees-z](https://forum.duplicati.com/user_avatar/forum.duplicati.com/kees-z/32/29_2.png) [@kees-z](https://forum.duplicati.com/u/kees-z)\
**Post date:** [April 16, 2019, 8:26pm UTC](https://forum.duplicati.com/t/why-is-the-13th-charcater-always-a-4/6843/3 "2019-04-16T20:26:14Z")

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That was very helpful, thanks for the link. I never realized that the filenames consist of UUID’s, I always thought it was just a bunch of random hex characters.