RAM usage of very small systems What is the absolute bare minimum RAM required for a full node.  So for example a pi zero with 512MB RAM, could that act as a full node?

If not what components are causing the RAM usage, my own theory is that the txleveldb is fully loaded to RAM?  If so as the chain gets longer, RAM usage will need to increase?
just look at the Page where its written Sir

https://bitcoin.org/en/full-node#special-cases

2 Gigabyte RAM you must have,  otherwise fail you will ;)

And what i forgot to say, it is not the length of the Blockchain, it is the mass on Data for Transactions, forwarding money, Blocks and so, Mempool simple.