Test cases are normally stored in repositories like

1.VSS - Test cases are written in excel sheets and stored 
module by module in VSS. There will be a separate folder 
alloted for test cases for every release.

2.Test director - In test director there is a separate 
location<tab> PLAN TEST. Here also we can create different 
folders and test set.

Thanks,
Harisha

If we do manual testing ,Test case store my Directory at 
example.exl format.If we follow the any automation tool 
store the given path.the path may be company server of your 
loging path.

Usually the testcases are stored into the common location 
or a Repository. This repository can within ur company's 
server or outside. Its all depands on company's policies. 
But, during an interview, it's always better to give a 
single answer.
Testcases can be in WinWord or Excel format and it should 
be easily available to all whenever required.

Its differ frrom company to company some comapnies stores 
inVSS,TD and Quality Centre.

Normally the test cases are stored in the Quality Center, 
Test Directory, Configuration Management Tool (VSS). It is 
basesd on the company it iwll be taken..