Big difference. You need to take care of the whole system, just like you would with a regular server, to keep everything up to date and secure, while on a managed server the company hosting you will most likely take care of all that.
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Cpanel itself doesn't means fully management. If you are not familiar with linux, I would suggest a fully managed VPS instead of unmanaged. With unmanaged VPS you will need to concern about about security, optimization, log checking, etc which might be trouble for you.
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