Computer Science Principles course

1. 1.Binary and Data

   Computers store everything, from numbers to photos to this sentence, as patterns of bits, each 0 or 1. Binary is base 2: each place is worth a power of two, so $1011_2 = 8 + 0 + 2 + 1 = 11$. Eight bits make a byte, which can hold $2^8 = 256$ different values.

   • $n$ bits can represent $2^n$ distinct values.
   • Convert decimal to binary by repeatedly dividing by 2 and reading remainders upward.
   • Hex digits: 0-9 then A-F for 10-15; $\text{FF}_{16} = 255$.
   Quick check: Convert $11010_2$ to decimal.

   $26$

   Includes a worked example, 3 common mistakes and 3 practice questions with answers. Study binary and data

2. 2.The Internet

   The internet is a network of networks that moves data in small chunks called packets. Each packet carries part of the message plus addressing information, and routers forward packets hop by hop toward their destination. Packets from one message may take different routes and arrive out of order; the receiving computer reassembles them.

   • IPv4 addresses are 32 bits ($\approx 4.3$ billion); IPv6 uses 128 bits.
   • DNS translates names like example.com into IP addresses.
   • Bandwidth is how much data per second a link carries; latency is the delay.
   Quick check: How many addresses does a 32-bit address space hold?

   $2^{32} = 4294967296$

   Includes a worked example, 3 common mistakes and 3 practice questions with answers. Study the internet

These topics belong to the course outline. Full explainers for them have not been written yet, so they are summarised here rather than given pages of their own.

Impact of Computing

Privacy, bias and the digital divide.

• Computer Science overview
• All subjects