Q51. What is the difference between unit, integration and end-to-end tests?
Unit tests exercise a single function, class or module in isolation, with dependencies replaced by fakes. They run in milliseconds, pinpoint failures and are cheap to wri...
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Q52. What are the main phases of a compiler?
A typical compiler pipeline has a front end, a middle end and a back end. - Lexical analysis: turn characters into tokens. - Syntax analysis: build a parse tree from the ...
Q53. Why use a DBMS instead of storing data in files?
A file system stores bytes in files and directories but knows nothing about their structure. A DBMS adds a layer that understands records, types, relationships and constr...
Q54. What happens when you type a URL into a browser?
The browser parses the URL, then finds the server's IP: it checks its cache, the OS cache, `/etc/hosts`, then asks a resolver, which recurses from the root servers throug...
Q55. What is the difference between user mode and kernel mode?
CPUs have at least two privilege levels. In user mode, code cannot execute privileged instructions or touch hardware or protected memory. In kernel mode, the OS kernel ca...
Q56. What is the difference between an abstract class and an interface?
An interface declares a contract: a set of method signatures with no state that any type can implement. A class can implement many interfaces, which models capability. An...
Q57. What is the difference between supervised and unsupervised learning?
Supervised learning uses labelled examples, learning a mapping from inputs to known outputs. Tasks include classification (predict a category, such as spam or not) and re...
Q58. What is the difference between ETL and ELT?
ETL extracts data from sources, transforms it on a separate processing engine, then loads the clean result into the target. ELT extracts and loads raw data into the targe...
Q59. What is the difference between a security group and a network ACL?
Both control traffic in a VPC, but at different layers. - Security groups are stateful and attached to ENIs or instances. Return traffic is automatically allowed. Rules a...
Q60. What is the difference between cache-aside and read-through?
Cache-aside (lazy loading): the application checks the cache first. On a miss it reads the database, then writes the value into the cache and returns it. The application ...