When you visit 'www.example.com' in a browser, your computer cannot route data to it until it has an IP address. Which service performs this translation and how is it structured?

HTTP — the web protocol converts domain names to addresses automatically DNS (Domain Name System) — a distributed hierarchy of servers from root, to top-level domain, to authoritative nameservers TCP — the transport protocol handles name-to-address translation Your router — it contains a complete database of all domain names

TCP provides 'reliable, ordered delivery' of packets. What does this mean, and what cost does TCP pay for these guarantees compared to UDP?

TCP and UDP are identical — 'reliable' just means the hardware is high quality TCP retransmits lost packets and reorders out-of-sequence ones, adding latency — UDP sends and forgets, which is faster but may lose data TCP delivers all packets simultaneously; UDP delivers them one at a time UDP is more reliable than TCP because it uses shorter packet headers

HTTPS adds TLS encryption on top of HTTP. What specific threats does HTTPS protect against that plain HTTP does not?

HTTPS prevents all SQL injection and cross-site scripting attacks HTTPS compresses data to make pages load faster Eavesdropping (intercepting data in transit) and man-in-the-middle attacks (impersonation), verified by a certificate authority HTTPS protects server data at rest from database theft

A database table 'Orders' has a column 'customer_id' that refers to the primary key of a 'Customers' table. What is 'customer_id' called, and what integrity rule does it enforce?

A primary key — it uniquely identifies each record in the Orders table An index — it speeds up lookups on the customer_id column A foreign key — it ensures every order references a customer that actually exists in the Customers table A constraint — it prevents the column from containing negative numbers

A query against a 50-million-row sales table takes 45 seconds without an index but 0.02 seconds after adding an index on the 'product_id' column. What does an index do to achieve this?

It caches the entire table in RAM, eliminating disk access It compresses the table so fewer bytes are read from disk It creates a sorted data structure (typically a B-tree) that allows the database to jump directly to matching rows rather than scanning all 50 million It splits the table across multiple servers for parallel processing

A retail website uses a relational (SQL) database for order history and a Redis key-value (NoSQL) store for session management. Why is this split architecture sensible?

Redis is always faster than SQL, so all data should eventually move to Redis The split is a mistake — all data should be in one database for consistency SQL excels at complex queries with relationships and ACID guarantees; Redis excels at extremely fast, simple key lookups for ephemeral data like sessions SQL cannot handle more than one table, so a second database is needed for sessions

What does the 'A' in ACID database properties stand for, and why is it essential for a banking transfer that debits one account and credits another?

Authentication — users must be authenticated before any transaction is permitted Atomicity — the debit and credit either both succeed or both are rolled back; there is no state where money disappears or appears from nowhere Availability — the database must be online 100% of the time Archiving — all transactions are permanently stored for audit purposes

A REST API uses HTTP verbs. A mobile app wants to retrieve a list of products. Which HTTP verb and URL convention is correct according to REST principles?

POST /products — POST is used for all data retrieval operations DELETE /products — DELETE retrieves and then removes the data GET /products — GET retrieves data without modifying the server state PUT /products — PUT is the universal HTTP verb for data operations

A SQL JOIN combines rows from two tables. If an 'Orders' table and a 'Customers' table share a 'customer_id' column, what does a JOIN allow you to do?

Merge the two tables permanently into one combined table Retrieve order details and customer names together in a single query, even though they are stored in separate tables Delete records from one table that do not appear in the other Duplicate all data across both tables for faster access

Packet switching routes individual data packets independently across the internet. Why is this more resilient than circuit switching (which reserves a fixed path for the entire communication)?

Packet switching always uses less bandwidth than circuit switching Circuit switching is obsolete — no networks use it any more If a router fails, packets can be dynamically rerouted around it — circuit switching would drop the entire connection Packet switching guarantees that all packets arrive in order, unlike circuit switching

A developer stores API keys in JSON responses sent to mobile app users so the app can authenticate API calls. What is the critical security flaw in this approach?

JSON cannot securely transport API keys — XML must be used instead Anyone who intercepts or extracts the key from the app can make authenticated API calls impersonating the app The JSON format adds too much overhead, slowing down API responses Mobile apps cannot use HTTPS, so all API keys are exposed anyway