I need your advice. Currently i am selling software but now i am planning to sell computers and laptop, so should i install cs-cart on subdomain or may be on same root domain, which one is good for SEO ?
sub-domain if your product lines are separate and distinct. If there is overlap then having it as a sub-directory of your main domain will bring better results.
Of course, like most SEO, this is an opinion versus fact.
on main domain csc already installed, just want to know can i add hardware items on root domain where csc installed or subdomain like hardware.abc.com ?
I would use the same shop where you sell the Software. First your Software customers see that you sell other product items, second it´s betther for SEO issue, because “Content is King” and the link juice get you complete shop what you have build on backlinks.
Or, if you have enough products to justify this, then setup an entirely new CS-Cart site like MiracleHardware.com and link them together.
Or, this would be a perfect example of where you could use the “Multi-Store” version to operate both stores (offering entirely different products on each) seperately while administering both through a single admin panel.