CS208 Introduction to Computer Systems
Wednesday, 14 January 2026

+ Try these questions for fun
- How many hexadecimal digits does it take to write one byte?
- What's the hexadecimal representation of the ASCII value of the space character?
       ("man ascii" is a handy command on most Unix systems)
- What integer does this int's 32-bit value represent? 0xFFFFFFF3
- What int do you have to add to 0xFFFFFFF3 to get 0?

+ Topics coming up
- Two's complement recap
- Byte order ("little endian" vs. "big endian")
- Representing characters
    - ASCII
    - Unicode
    - Encodings: UTF-16LE, UTF-16BE, UTF-8

+ Recap: N-bit two's complement integer representation
- Recognizing >= 0 vs. < 0 integers (leftmost bit = 1 ==> # is negative)
- Negation: complement, then add 1
- Addition works
- Negatives: "what do I have to add to this number to get 0?"
- char (8-bit = 1-byte integer)
    vs. short (16-bit = 2-byte)
    vs. int (32-bit = 4-byte)
    vs. long (64-bit = 8-byte)
        These bit lengths are compiler-dependent

+ Byte order
- The problem
- The two solutions
- Why it's all kinda sad

+ Characters
- https://sandbox.jeffondich.com/encoder
- International agreements mapping character <--> integer
    - ASCII [but remember "A" stands for "American"]
    - ISO-8859-1 ["I" stands for "International"]
    - Unicode
- "codepoint" - the integer that represents one character
    U+00E9 <-> é
- "encoding" -- and why it's different from "codepoint"
    - given a codepoint, how am I going to store it
        as a byte sequence? (in memory or in a file)
- Easy encodings
    - UTF-16LE
        α <-> U+03B1 <-> B1 03 [2-byte sequence]
    - UTF-16BE
        α <-> U+03B1 <-> 03 B1 [2-byte sequence]
----
- Harder, but important
    - UTF-8