Two men worked a large saw with a handle at each end ( about 4 to 6 foot long).
One was in a pit and the other up above and they cut planks from the tree trunk that was laid over the hole of the pit.
This was prior to the introduction of steam driven saws.
Bloody hard work and worse for the poor beggar in the pit getting covered in saw dust.
If you look closely at some old weather boards and the like you can see the rough sawn pattern on the wood.