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Stuff Every Technology Expert Should Know

How computers, networks, the internet, software and security really work, one card at a time.

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  1. How many bytes are in one kibibyte (KiB)?
    Show the answer

    1,024 bytes. The SI prefix kilo means 1,000. The binary prefix kibi (Ki) means 2 to the 10th, which is 1,024. Storage labels often use GB, while some software reports binary-sized GiB.

  2. How many bits does one hexadecimal digit (0 to F) stand for?
    Show the answer

    4 bits. Hex has 16 symbols, and 4 bits make exactly 16 patterns. So every byte (8 bits) is written as two hex characters, like FF for 255. That neat fit is why programmers love hex.

  3. Base64 encoding turns every 3 bytes of data into how many text characters?
    Show the answer

    4 characters. Base64 takes 24 bits (3 bytes) at a time and splits them into four 6-bit groups. Each 6-bit group becomes one of 64 printable characters. Four out for every three in means about 33% growth.

All 165 practice questions

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  1. How many bytes are in one kibibyte (KiB)?
  2. How many bits does one hexadecimal digit (0 to F) stand for?
  3. Base64 encoding turns every 3 bytes of data into how many text characters?
  4. How many different values can 8 bits represent?
  5. How do nearly all computers store negative whole numbers in binary?
  6. What is the range of an 8-bit signed (two's complement) integer?
  7. How many bits does standard ASCII use for each character?
  8. In UTF-8, how many bytes can one Unicode scalar value take?
  9. A plain ASCII text file is read as UTF-8. What happens?
  10. What is the highest code point Unicode allows?
  11. Which Unicode character is used as the byte order mark (BOM) at the start of some text files?
  12. Why does Python report 0.1 + 0.2 == 0.3 as false?
  13. How many bits of precision does a standard 64-bit double (IEEE 754 binary64) number have?
  14. When small rounding errors are acceptable, how should two floating point results be compared?
  15. Moore's law says the number of transistors on a chip doubles about how often?
  16. Around 2004, why did chipmakers shift from faster clocks toward multicore processors?
  17. With Intel Hyper-Threading on, how does one physical core appear to the operating system?
  18. A phone chip mixes fast, power-hungry cores with slow, efficient ones. What is that design called?
  19. Compared with a CPU, what does a GPU spend more of its transistors on?
  20. Why does DRAM, the main memory in a computer, need to be refreshed every few milliseconds?
  21. CPU cache is built from SRAM. Why isn't all of a computer's memory SRAM?
  22. On a cache miss, how much data does a typical modern CPU cache pull in from memory?
  23. In a CPU with L1, L2 and L3 caches, which level is smallest and fastest?
  24. A loop reuses the same few variables thousands of times. Which kind of locality is that?
  25. Which of these loses its contents when the computer loses power?
  26. Flash memory cells wear out after many writes. How does an SSD stretch its life?
  27. Why isn't overwriting a file with zeros a reliable way to erase it from an SSD?
  28. What is the main reason a hard disk drive is so much slower than RAM or an SSD?
  29. What is the operating system kernel?
  30. On Windows, what happens if a kernel-mode driver crashes?
  31. Threads inside the same process share most things. What does each thread get its own copy of?
  32. What does a CPU's TLB (translation lookaside buffer) store?
  33. With virtual memory, what data structures map virtual addresses to physical RAM addresses?
  34. On a Linux ext4 file system, where is a file's name stored?
  35. Why won't a 6 GB video file copy to a USB stick formatted as FAT32?
  36. How many partition entries does a classic MBR partition table hold?
  37. With UEFI Secure Boot turned on, what does the firmware check before running boot software?
  38. When a computer starts, what is the boot loader's job?
  39. What makes a bare metal (type 1) hypervisor different from a hosted one?
  40. Several containers run on one Linux host. What do they all share?
  41. A C program is spread over several source files. Which tool joins the object files into one executable?
  42. Before execution, what does CPython compile source code into?
  43. What does the Java Virtual Machine actually run?
  44. ARM processors in phones use what kind of instruction set design?
  45. How does IP treat separate datagrams?
  46. Which sequence matches the Internet protocol suite from top to bottom?
  47. How many layers are in the OSI reference model?
  48. How many bits long is an IPv4 address?
  49. What did IANA's final recovered-pool IPv4 allocation mean?
  50. Which IPv4 block is reserved for private internets?
  51. How can NAPT let many private hosts share one public address?
  52. How long is the most common Ethernet MAC address?
  53. Which DHCP message confirms a client's configuration parameters?
  54. What may a DNS resolver receive when a server lacks the final answer?
  55. What does a DNS record's TTL control?
  56. What service does TCP present to an application?
  57. Which protection does UDP itself not guarantee?
  58. What is the default TCP port for an HTTP URI?
  59. Which port does an SSH server normally listen on?
  60. Which server port does DNS use with both UDP and TCP?
  61. What does the HTTP GET method request?
  62. What does the HTTP POST method ask the target resource to do?
  63. What does HTTP status 301 indicate?
  64. Which threats is TLS designed to resist during communication?
  65. What does a public-key certificate bind together?
  66. What does network bandwidth describe?
  67. What does network latency measure?
  68. What does network throughput measure?
  69. Which ICMP exchange is the basis of ping?
  70. How does traceroute reveal successive routers along a path?
  71. Which Wi-Fi band typically travels farther, 2.4 GHz or 5 GHz?
  72. What does the Wi-Fi Alliance call Wi-Fi 6 (802.11ax) extended into the 6 GHz band?
  73. What is a router's core forwarding role?
  74. How does an Ethernet switch dynamically build its address table?
  75. Why does a CDN serve cached content from edge locations?
  76. What kind of routing protocol is BGP?
  77. Which cloud model lets the consumer run operating systems and applications?
  78. In PaaS, what does the consumer control?
  79. What does a SaaS consumer primarily use?
  80. Why do data centers use redundant power and network systems?
  81. Which medium is less susceptible to electromagnetic interference, fiber or copper?
  82. How fast is binary search on a sorted array of n items, in Big O terms?
  83. What must be true about a list before you can use binary search on it?
  84. In Big O notation, what do you ignore when describing an algorithm's running time?
  85. What is the worst-case running time of insertion sort on n items?
  86. Merge sort splits a list in half, sorts each half, then merges. What is its running time?
  87. On average, how long does looking up a key in a hash table (like a Python dict) take?
  88. In a hash table, what is a collision?
  89. How does a linked list keep its items in order?
  90. Why is inserting at the front of a Python list slow when appending at the end is fast?
  91. A stack is last-in, first-out. Which item comes off a stack first?
  92. Appending to a dynamic array sometimes copies everything, yet it is still called O(1). Why?
  93. Why do binary search trees try to stay balanced?
  94. Using adjacency lists, what is breadth-first search's running time on a graph?
  95. In a recursive function, what is the base case?
  96. Why does Python have a recursion limit?
  97. What does it mean that a sorting algorithm is stable?
  98. How does Git think about the history of your project?
  99. What is the long hexadecimal code that names a Git commit?
  100. In Git, what actually is a branch?
  101. When does Git do a fast-forward merge?
  102. What is Git's staging area, also called the index?
  103. A bug appeared sometime in your last 1,000 commits. What does git bisect do?
  104. What is the key idea of a copyleft license like the GNU GPL?
  105. The MIT License lets almost anyone reuse code. What is its main condition?
  106. Which of these is NOT one of JSON's built-in value types?
  107. REST APIs are stateless. What does that mean for each request?
  108. Which HTTP method is not defined as idempotent, so repeating it can create duplicates?
  109. An HTTP status code starting with 5, like 500, means what?
  110. In a relational database, what two rules does a primary key enforce?
  111. Database indexes speed up searches. What is their cost?
  112. A bank transfer takes money from Alice and gives it to Bob. Why wrap it in a transaction?
  113. In ACID, what does Durability promise?
  114. What is a common difference between NoSQL and relational databases?
  115. SQL is called a declarative language. What does that mean?
  116. In functional programming, what makes a function purely functional?
  117. What is the difference between a unit test and an integration test?
  118. According to MIT's software course, what should you do first when hunting a bug?
  119. What caused the Y2K problem?
  120. What happens to a signed 32-bit Unix time counter in January 2038?
  121. On a website, where does backend (server-side) code run?
  122. After DNS finds the server's IP address, how does the browser open a TCP connection?
  123. While building a page, what makes the browser pause parsing the HTML?
  124. What does the HTTP header Cache-Control: no-cache actually mean?
  125. Your browser asks if its cached file changed and gets 304 Not Modified. What happens?
  126. Which three goals form the CIA triad?
  127. Which password property most directly increases resistance to guessing?
  128. What does current NIST guidance say about password composition rules?
  129. What should a service check when a user creates a password?
  130. Why is a unique salt added before hashing a password?
  131. What does bcrypt's work factor control?
  132. What makes authentication truly multi-factor?
  133. Why can a WebAuthn passkey resist a lookalike site's login prompt?
  134. What separates phishing from an ordinary unwanted message?
  135. How does a classic computer virus replicate?
  136. What distinguishes a classic worm from a virus?
  137. What defines a Trojan horse program?
  138. What does file-encrypting ransomware do before demanding payment?
  139. What does the principle of least privilege require?
  140. Which step makes patch management more than simply installing updates?
  141. What makes an attack a zero-day attack?
  142. What key does symmetric encryption use to encrypt and decrypt?
  143. What keys make asymmetric cryptography asymmetric?
  144. Which keys create and verify a digital signature?
  145. What does a TLS 1.3 key exchange establish for protecting data?
  146. Who can decrypt an end-to-end encrypted MLS application message?
  147. What can a messaging provider sometimes learn despite encrypted content?
  148. Where does a remote-access VPN tunnel's protection end?
  149. What happens to ordinary internet traffic during split tunneling?
  150. Which information commonly drives a basic firewall ruleset?
  151. What extra context does a stateful firewall remember?
  152. How do parameterized queries block SQL injection?
  153. Why must XSS output encoding match the browser context?
  154. Why should at least one backup be isolated from production systems?
  155. What does a restore test prove that a backup job report cannot?
  156. Why is a mirrored RAID array not a backup?
  157. About how much downtime does 99.9% monthly availability allow?
  158. What reliability problem is redundancy designed to remove?
  159. What must happen during a successful failover?
  160. Why should every logging host use a common time source?
  161. What does a SIEM add beyond collecting log files?
  162. Which activities belong in an incident-handling capability?
  163. What is the immediate goal of incident containment?
  164. What does incident eradication remove after containment?
  165. How can a service verify an age threshold while collecting less data?