What is the architecture of salesforce software?

Salesforce uses a cloud-based "multi-tenant" architecture.

"Cloud Based" meaning that you do not install software locally on a server. Salesforce software is accessed over the internet (the cloud) on Salesforce servers. The Salesforce database is actually Oracle on the back end by the way. This is very nice article and useful information please keep going.tekclasses is the best online salesforce training company from India bangalore

The analogy salesforce uses frequently to describe "multi-tenancy" is an office building. Like an offie building, Salesforce users have secure barriers (likes walls in an office) that divide your business from someone else's business (and your data!). However that office building that you share provides all the structure (stairs, elevators) and utilities (power, water, etc). In a multi-tenant architecture you don't have a single installation for your Salesforce instance - you're really a sub-set of a much larger database. SAlesforce keeps your configuration unique by storing meta-data about all your customizations even though you're running on a shared database. You share Salesforce.com's services (think the "utilities" analogy aforementioned) such as the security model, the ability to access Salesforce on mobile devices, API services, etc..