all these 3 ie. viewstate, cookies and hiddenfeilds comes under client side state management only.
Cookies.
for more refer:
http://webhacking.org.ua/117.htm[
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A cookie is a small text file on the client machine either
in the client's file system or memory of client browser
session. Cookies are not good for sensitive data. Moreover,
Cookies can be disabled on the browser. Thus, you can't
rely on cookies for state management.
View State
Each page and each control on the page has View State
property. This property allows automatic retention of page
and controls state between each trip to server. This means
control value is maintained between page postbacks.
Viewstate is implemented using _VIEWSTATE, a hidden form
field which gets created automatically on each page. You
can't transmit data to other page using view state.