Encodings — Class 11 ISC Computer Science revision notes
A 3-page visual revision sheet for Encodings, written for Class 11 ISC Computer Science. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.
Page 1 as PDF
Encodings in one look
how a fixed number of bits is made to carry a sign, a fraction and a character
A fixed width forces a choice
- a machine word holds a fixed number of bits, so every scheme below is a decision about what those bits are spent on
- an unsigned 8 bit pattern counts 0 to 255, because all eight bits carry magnitude
- the moment negatives are wanted, one bit has to say which sign, and the range paid for it
- nothing in the pattern itself says which scheme is in force: 10000101 is 133 unsigned, minus 5 in sign magnitude and minus 123 in 2's complement
Three ways to write a negative number
- leading bit is the sign, 0 for plus and 1 for minus, the rest is plain magnitude
- easy to read, but two patterns mean zero and adding needs the signs compared first
- negate by flipping every bit
- still two zeros, and addition needs the end around carry
- negate by flipping every bit and adding 1
- one zero only, and ordinary addition just works, which is why hardware uses it
What n bits can hold
- unsigned
0 to 2^n - 1 - sign magnitude
-(2^n-1 - 1) to +(2^n-1 - 1), with two zeros - 1's complement
-(2^n-1 - 1) to +(2^n-1 - 1), with two zeros - 2's complement
-2^n-1 to +(2^n-1 - 1), one zero
Page 1 of 3. The full sheet, all 3 pages, opens free in the app.
What this Encodings sheet covers
- A fixed width forces a choice
- Three ways to write a negative number
- Sign magnitude
- 1's complement
- 2's complement
- What n bits can hold
- unsigned
- Write -5 in 8 bit 2's complement
- Real numbers: mantissa and exponent
- Single against double precision
- Single, 32 bits
- Double, 64 bits
- Why it matters
- The catch
- Operations the paper asks about
- Characters are numbers with a lookup agreed in advance
- ASCII against Unicode
- ASCII
- Unicode
- Terms to use exactly
- Why sign magnitude lost
- Traps that cost marks
- Tricks that save time
How CapCompass uses this sheet
These notes are not a standalone PDF. CapCompass plans Computer Science chapter by chapter against your real exam dates and free hours, and when the plan reaches Encodings the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.
More Computer Science Class 11 revision notes
- Arrays and Strings
- Basic Input Output and File Handling
- Implementation of Algorithms
- Introduction to Object Oriented Programming using Java
- Methods and Constructors
- Numbers
- Objects and Classes
- Packages
- Primitive Values, Wrapper Classes and Types
- Propositional Logic and Hardware Implementation
- Recursion
- Statements and Scope
- Trends in Computing and Ethical Issues
- Variables and Expressions