Comparisons

An A record points a name at an IPv4 address; a CNAME makes a name an alias of another name. The rules, the apex restriction and when to use each.

IPv4's 32-bit addresses ran out; IPv6's 128-bit addresses do not. How the two differ in notation, headers, configuration, NAT and everyday administration.

TCP delivers every byte in order over a connection; UDP sends independent datagrams with no guarantees. What each costs and which protocols use which.

A 301 says a page has moved for good; a 302 says it is elsewhere for now. How search engines, browsers and request methods treat each, plus the 307 and 308 variants.

A hash fingerprints data, an HMAC adds a shared secret so only key holders can make or check it, and a digital signature uses a private key so anyone can verify who signed.

MD5 is broken, SHA-256 is the fast general-purpose hash, and bcrypt is a deliberately slow password hash. What each is for and which to use.

Symmetric encryption uses one shared key and is fast; asymmetric uses a public/private key pair and solves key exchange. Why real systems use both.

Single-precision, double-precision and decimal number types compared: bits, digits of precision, range, the 0.1 + 0.2 problem and when to use each, with values taken from NumPy and Python.

Three configuration formats compared: comments, readability, data types, pitfalls and typical uses, with the same configuration written in all three and checked to parse to identical data.

Random UUIDs, time-ordered UUIDs and ULIDs compared: bit layout, text length, sorting, database index behaviour and when to use each, with example values decoded and checked.

JSON for APIs and data exchange, YAML for hand-edited configuration, XML for documents and schema-heavy standards. Syntax, types, pitfalls and when to use each.

Which image format to use: JPEG for photos everywhere, PNG for lossless graphics, WebP and AVIF for smaller files on the modern web. Features compared.

When to compare means with a t-test and when with ANOVA: the number of groups, the multiple-comparison problem with its error rates, and why F equals t squared for two groups.

Three ways to describe the middle of a data set. When the mean misleads, why the median resists outliers, and when the mode is the only sensible choice.

Two ways to compare an outcome between two groups: how they are calculated from a 2 × 2 table, why they agree for rare outcomes and diverge for common ones, and which to report.

A 15-year mortgage costs far less interest but has a much higher payment; a 30-year loan is cheaper monthly and more flexible. Worked $300,000 example.

APR is the stated yearly rate without compounding; APY is the effective yearly rate once compounding is counted. Which one to read when borrowing and when saving.

The avalanche pays the highest interest rate first and costs the least; the snowball pays the smallest balance first and wins on momentum. A worked example with real numbers.

Investing everything at once versus spreading purchases over time: a worked example in a dip-and-recover market and a steadily rising one, and what each approach protects you from.

Traditional IRAs give a tax break now and tax withdrawals later; Roth IRAs tax contributions now and withdrawals never. The marginal-rate rule, worked out.

Simple interest is paid on the original amount only; compound interest is also paid on past interest. The formulas, a $10,000 example and where each is used.

BMR is what your body burns at rest; TDEE adds movement, exercise and digestion. Why TDEE is the number to plan calories around, with a worked example.