The CPU and the fetch-decode-execute cycle
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Apuntes de la lección
What the CPU does
- The central processing unit (CPU) is the "brain" of a computer. It fetches instructions from memory, decodes them and executes them.
Components
- ALU (arithmetic logic unit): performs calculations and logical comparisons.
- Control unit (CU): directs the operation of the CPU, controlling the flow of data and instructions.
- Registers: very fast storage inside the CPU: program counter (PC) (address of the next instruction), memory address register (MAR), memory data register (MDR), accumulator (ACC) (stores results).
- Cache: small, very fast memory close to the CPU holding frequently used data.
CPU components
The fetch-decode-execute cycle
- Fetch: the PC's address is copied to the MAR; the instruction at that address is fetched into the MDR; the PC increments.
- Decode: the control unit decodes the instruction.
- Execute: the instruction is carried out (the ALU may calculate).
Fetch, decode and execute
Performance
- Clock speed (GHz: cycles per second), number of cores (more can run tasks in parallel), and cache size affect speed.
Multiple processor cores
Von Neumann architecture
- Instructions and data are stored in the same memory. Embedded systems (e.g. washing machine controller) are dedicated computers.
Diapositivas
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Preguntas de práctica
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1.What does CPU stand for?
Easy- Acentral processing unit
- Bcentral program unit
- Ccomputer processing unit
- Dcore processing utility
2.What does ALU stand for?
Easy- Aarithmetic logic unit
- Ball logic unit
- Canalogue logic unit
- Darray logic unit
3.What does the control unit do?
Easy- Adirects the flow of data and instructions
- Bperforms calculations
- Cstores files
- Ddisplays output
4.What is a register?
Easy- Aa small, fast storage location in the CPU
- Ba hard drive
- Ca network card
- DRAM
5.What is cache memory?
Easy- Asmall, very fast memory close to the CPU
- Bslow storage
- Ca hard drive
- Da printer
6.What does the PC hold?
Easy- Athe address of the next instruction
- Bthe result
- Cthe current data
- Dthe clock speed
7.What does the MAR hold?
Easy- Athe address of the memory location being accessed
- Bthe data
- Cthe instruction
- Dthe result
8.What does the MDR hold?
Easy- Adata transferred to or from memory
- Bonly a memory address
- Conly the clock frequency
- Donly the result of every addition
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