please excuse me for the noob like question. But I am asking since I use Electrum and do not run bitcoin-core.

In what form does the blockchain exist on full nodes, is it as a single file or a collection of files ? If more than 1 file are they numbered in any way ?  I am almost certain it is not a single 60+ GB file, since all OSes may not support that.

Does the actual blockchain contain extra data besides the actual blocks (meta data for indexing etc.)?