Is there any difference between address that have Smart Contract and “normal” one?

Is there any difference between address that have smart contract on it, and “normal” address (address that You can create private and public key pair)? For more context, this is the problem I’m thinking about: Let’s assume that Smart Contract has address 0xfoo, and we – either by pure random chance, or we generated somehow…

Are simultanous transactions possible (basic but potentially very dangerous security concern…most likely impossible…)?

Long story short I am curious how a contract stores variables in memory, so is it possible to spam say 100 transactions at once and the values to be changed afterwards…I am sure I am giving bad description so here is the code to better illustrate my point: contract thiscontract { uint256 balancer = 3000;…