tpa file format
Main Table of Contents VERSION 5.0-20140629-b0f0873-dirty-unknown

Description

The tpa file extension stands for binary run input file. This file contains the starting structure of your simulation, The molecular topology and all the simulation data. Because this file is in binary format it cannot be read with a normal editor. To read a binary run input file type: 
% gmx dump -s topol.tpa
or if you're not such a fast reader: 
% gmxdump -s topol.tpa | more

You can also compare two tpa files using: 

% gmx check -s1 top1 -s2 top2 | more

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