It is stored in client side.
It is stored in an encrypted format.

variables are stored in the browser.
viewstate can hold only string data or serialisable objects

viewstate is the client side state management.every server 
control  has a view state .we can assign a property named 
Enableviewstate to every server control  and setting the 
property to true,the viewstate will be enabled and hence 
the values of the control will be stored as encrypted 
format whenever the page is postback from the server again 
and again.

Viewstate values are saved in the format of Hash.

ViewState will be rendered as HTML Hidden field with 
encryption of data inside it

View state is stored in the client in the form of a hidden
control called “__VIEWSTATE”. Here by client I mean the
rendered aspx pages in the browser. If view state property
is set to true then ASP.NET automatically adds a hidden
field/control by the name “__VIEWSTATE” and stores the
information related to the state of the page in an encrypted
format.

ViewState Data is stroed in Base64 encoded format.

Viewstate is stored in hash format and it will be stored in
hidden field named "_Viewstate".