The line between decentralised and centralised wallets is blurred. Electrum lets you keep your private key but connects to the Bitcoin network through one of a limited number of servers. Blockchain.info lets you keep your private key but you must access the Bitcoin network through its website. Coinbase is fully centralised because you don't know your private key, but Electrum and Blockchain.info are partly centralised.
How is electrum centralised when your private keys never leave your pc and you can do what ever you like with your coins. The only thing electrum needs is an internet connection. Centralized mean some central supreme authority watching over you and making decisions for you, decentralized mean no central authority, you are free to do what you like, thats the big difference between Electrum and Coinbase which don't let you know your private keys.
Electrum's wallet connects to the Bitcoin network through one of a number of servers. One of those servers is what relays all your transactions to the Bitcoin network. You have to trust the server isn't malicious. If it's malicious your Bitcoins are less secure. With the full Bitcoin core wallet it doesn't matter if your wallet connects to a malicious node because it connects to multiple nodes at the same time, and ignores any malicious one.
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Is that part of the system decentralised, or is that part of the system centralised?
Electrum is stored on your device but relies on servers for transactions information. Some wallets store the entire blockchain but electrum does not. Wallets that do not store the blockchain locally are called lightweight wallets. Lightweight wallets have to query their servers each time they are run.
So are you suggesting me to switch to Bitcoin Core, I can install it in my laptop as in my PC I don't have that much space left. Is Bitcoin core more secure than electrum, if thats the case I am giving it a try, hopefully it will run on Linux.
