Relation between "Block Size"and "Upper Limits" in ext2

A similar looking question asks for the reason why the upper file limit could be 2 TB in ext2. I am trying to understand but the Documentation on ext2 but find this hard. Please correct me if I'm wrong: - Blocks can be 1 - 4 KB in size - available amount of blocks is based upon a 32-Bit value: 232 = 4.294.967.296 blocks In the documentation I found: 231-1 = 2.147.483.647 addressable Blocks. I miss 2.147.483.649 Blocks. My **guess** is that this is »reserved« for the *Superblock*, the *Block Group Descriptors* , their backups etc. (correct?) Question ---------- **How exactly are the file size limits calculated in ext2** And, just in advance: Is – and if so – how far can this be translated to ext3 and ext4 (or other file systems... please?) – I'm still far from them and not lazy to look this up myself; just confused about where the basics come from .