In which E-Commerce system architecture, a web server responds to requests for…

E-commerce systems are commonly classified by how many distinct server-side layers, or "tiers," separate their responsibilities. A two-tier architecture is organized into exactly two server-side layers: a web server that serves web pages (and typically also carries the application/business logic) and a database server that stores data, with no additional layer between them. A three-tier architecture is organized into exactly three server-side layers: a presentation/web server, a dedicated application server that carries the business logic, and a database server. Multi-tier (n-tier) architecture is the general term for a system organized into three or more server-side layers -- it generalizes three-tier and beyond, for example with separate presentation, business-logic, integration, and data layers.

The question describes only two components: a web server that responds to requests for web pages, and a database server that provides backend data storage. No additional application/business-logic server layer is mentioned anywhere in the description. This matches an architecture organized into exactly two layers, where the web server itself carries out presentation and business logic while the database server is a separate, second layer used purely for data storage.

• Three-tier architecture is defined by exactly three server-side layers; only two layers are described here.

• Multi-tier architecture is defined by three or more server-side layers; only two layers are described here.

• "Both two-tier and multi-tier" would require the same system to simultaneously have exactly two layers and three or more layers, which cannot both hold for one architecture at once.

Cross-checking against the official answer key for this exam confirms the same result: the two-layer description given in the question matches two-tier architecture.