What is the difference between On Premise and SharePoint Online?

SharePoint On-premises SharePoint Online
Environment Comparisons
SharePoint farm is in Organization’s own premise. SharePoint sites are in the Microsoft Data Centre (MDC).
Organization’s IT and support team manages patches and upgrades. Microsoft itself applies patches and upgrades
On-premise has version numbers: SharePoint 2013, SharePoint 2016, etc... Online Does not have a version number
Information/Data/Content is stored in Organization’s own servers. Can be the option for strict data privacy requirement.  Information/Data/Content is stored in cloud
Organization has full control over the servers, hardware and entire infrastructure. Microsoft owns data centres. Organization doesn’t have any control over the servers.
Organization has the responsibility to keep the “Uptime” of the server as it is managed by the organization itself. SLA with Microsoft of 99.9% availability
Feature Comparisons
Need to purchase and maintain Hardware. Software licenses need to purchase. Annual Subscriptions for Office 365 are billed on per user basis
Full support for server side and client side code Full support for client side code. Very limited support for server side code
Full Trust code can be deployed Full trust code cannot be deployed
Features with farm and web application level can also be deployed Maximum scope of feature deployment is site collection level.
For storage, devices can be expensive. Also the extension of the storage limit can cost Organization more and as the data grows, Organization will need to keep adding storage limits causing more expense to Organization. Storage cost is cheap. Cost may vary according to the selection of plan to be purchased. 
Fully Customizable as the entire control is with organization. Limited customization as the server controls are with Microsoft.
Full access on windows and SQL servers No server access is given to the users.
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