About how restoration of an Electrum Wallet works

[patrick_here]

A newbie question about Electrum Wallet:

I understand that I can store multiple bitcoins (or bitcoin transactions) in an Electrum Wallet located on my (Linux) computer and that the wallet contains a private key and it can be restored from a passphrase.  However, what I don't understand is this:

Suppose I have three bitcoin transactions in my local wallet and then my hard drive crashes without a backup and all I have is my Electrum Seed ...so I go ahead and re-create my Electrum wallet.
Will my newly-recreated wallet have my three bitcoins (or bitcoin transactions) in it?  If so, where did it get this information from (since my HardDrive crashed) ...did it get it from the blockchain? 

Please do not post an "answer" this question unless you really know the answer. 

Thanks in advance for the reliable information

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[Abdussamad]

The blockchain records all bitcoin transactions. Electrum gets access to the blockchain via electrum servers. These are run by volunteers. You can learn what server you are connected by going to tools > network or the console tab (view > show console if you can't see it).

Your wallet contains the private keys that let you control the values (bitcoins) recorded in the blockchain. All the private keys in your wallet are derived from the seed so when you restore from seed electrum can discover your entire transaction history. What it can't recover are your labels and contacts. These things are only stored in your wallet file so be sure to back that up regularly via file > save copy or by having your backup app automatically grab it from the electrum wallets directory

[jackg]

Yes that's exactly what it does.

Your seed is a very long number broken down into 13-15 words so it's easier to store/write down/remember.

If you want to restore the wallet, the words are converted into this number that then produces a series of private keys that you can spend from. These private keys are converted into addresses also so the data can be recieved on those addresses. A hash of that seed number is also used to produce an extended public key which is then used to be sent off to an electrum server in order for the data to be sent back of the transactions for the entire wallet data to be restored (labels and other data that are just on your device don't return however, that's useful to remember).

[patrick_here]

.... an extended public key which is then used to be sent off to an electrum server...

   [Edited] ...okay thanks for the replies.  Just noticed that the Electrum Server Software is available ("ElectrumX")

[Abdussamad]

Electrum doesn't share the extended public key aka master public key with electrum servers. It asks for relevant transaction data by sharing your addresses script hashes relevant to your wallet [1] with the server. The distinction is important because exposure of the MPK is bad for your security and the MPK tells you all the addresses that can ever be generated in your wallet even ones that you haven't actually generated yet.

[1] Edit: I just learned on IRC that Electrum no longer shares the address with the server. Instead it subscribes to transactions relevant to the output script aka scriptpubkey:

https://electrumx.readthedocs.io/en/latest/protocol-basics.html#script-hashes

Of course if the server operator wants to he can find out the address from this but it's one extra step he has to take.