Review: Binary #
- 10101 to decimal
- 35 to binary
Negative Numbers #
Concept: Sign bit (initial 0 bit means positive)
Concept: Two’s complement (flip all the bits, add 1)
Fixed point numbers #
Decimal $3.25
Binary point, 1/2, 1/4, etc.
Floating point numbers #
E2M1
4 bits:
- Sign bit
- Exponent (2 bits)
- Mantissa (1 bit)
Complications:
- Exponent bias
- Subnormals
- NaN / inf
Normals: value = (-1)sign × 2(exponent - 1) × (1 + mantissa / 2)
Subnormals: value = (-1)sign × 20 × (mantissa / 2) (just 0.5)
Values: 0, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 6.0
IEEE 754 binary 32
- Sign
- 8 bit exponent
- 23 (+1) bit mantissa / significand
Text #
Encoding in lab: Caesar cipher is easy as addition:
- Convert letter to number, add 3, convert number to letter?
- A = 1, B = 2, …, ?
- 5 bit = 32 chars, 6 bit = 64, 7 bit = 128
- ASCII = 7 bit, A = 65, a = 97, 1 = 49, . = 46 (python
ord) - We really use 8 bits, per character:
- Top bit 0: rest is an ascii code
- Top bit 1: multi-byte character, non-ascii
- Text is a series of bytes.
- For English keyboard chars, each byte is one character.
- So the text “Hi, Welcome to CS 2010” is 22 bytes.
Structure of a Computer #
- CPU
- RAM
- Disk
- I/O: Keyboard, screen, network
Where do we store data? #
- Running program: in RAM
- Longer than one program? On disk, in a file.
- A file is a series of bytes, with a name (short text)
Demonstrate file <-> bytes and different UI modes #
- Use gedit to create sample file
- Use nemo to show properties:
- Name
- Size in bytes
Two user interface modes:
- GUI, like gedit/nemo
- gives a single clear view
- common actions are visual and discoverable
- Less common actions are hidden or entirely missing
- CLI, repeat with echo/ls/stat/vim
- “we can do better than point and grunt: language”
- communicate with text: commands and command output
- Need to know the language(s), both concepts and grammar
hd (FILE)man ascii- Absolutely need to read some docs.
- Option 3: Natural language
- opencode - Gemma
- “Create a text file named ‘hello.txt’ containing ‘Hello, CS 2010’”
- What are the ascii codes for the characters in the file?
- Append a snowman emoji to the end of the file.
- Still need to know the concepts, although but there’s some improved discoverability through discussion.
