Computer Hardware — Class 12 ISC Computer Science revision notes
A 4-page visual revision sheet for Computer Hardware, written for Class 12 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
Computer Hardware in one look
seven gates, two of them enough on their own, and the circuits built out of them
Seven gates, and what each one answers
- NOT inverts, AND is true only when all inputs are true, OR is true when at least one is
- NAND and NOR are those two followed by an inversion, and the bubble on the symbol is what marks it
- XOR is true when the inputs differ, and XNOR is true when they agree, so XNOR is the equality detector
- a gate is a physical circuit, so its truth table is a description of voltages, not of an abstract formula
Why NAND and NOR are called universal
- a set of gates is universal if AND, OR and NOT can all be built from it alone, because everything else is built from those three
- NAND alone: tie both its inputs together and it inverts, so NOT is free; a NAND then a NOT gives AND; NOT on each input then a NAND gives OR
- NOR alone does the same job by the dual route, and both facts follow directly from De Morgan
- chips are made largely of one gate type because one repeated cell is cheaper to fabricate than seven different ones
Page 1 of 4. The full sheet, all 4 pages, opens free in the app.
What this Computer Hardware sheet covers
- Seven gates, and what each one answers
- Why NAND and NOR are called universal
- Adding, in hardware
- The adder outputs as expressions
- half adder Sum
- half adder Carry
- full adder Sum
- full adder Carry
- Three combinational blocks the paper names
- Sizes worth remembering
- 8 to 3 encoder
- 3 to 8 decoder
- 4 to 1 multiplexer
- The select rule
- Decoder against multiplexer
- Decoder
- Multiplexer
- From an expression to a circuit, and back
- 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 Computer Hardware 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.