The Von Neumann Model
Fundamental Components
The classic organization of modern computers relies on sequential processing and unified storage of data and instructions.
Main Units (CPU)
The microprocessor brings together two key components:
- ALU (Arithmetic and Logic Unit): Performs computations (+, -, AND, OR).
- Control Unit (CU): Sequences instruction execution and orchestrates data transfers.
Buses and Main Memory
Components communicate via interconnect buses:
- Address bus: Carries the targeted memory location.
- Data bus: Transfers the instruction or data.
- Control bus: Signals read/write commands (R/W).
Instruction Cycle Simulator
Fetch — Decode — Execute
Step through the processing of an assembly program within the processor's registers (PC, IR, ACC).
Sequential Execution in the CPU
Click Next Step to watch the instruction pointer (PC) advance and the registers update.
Memory Hierarchy
Registers, Caches, and RAM
A fundamental trade-off between access speed, storage capacity, and manufacturing cost.
Average Memory Access Time (AMAT)
Average memory access time depends on the cacheHit Rate:
AMAT = Tcache + (1 - H) × PenaltyRAM
Where H represents the percentage of accesses found directly in cache memory (L1/L2/L3).
Principle of Locality
- Temporal Locality: Data that was just accessed is likely to be reused soon (e.g. loops).
- Spatial Locality: Data contiguous in memory is likely to be accessed shortly after (e.g. arrays).
Test your knowledge
Question 1: Which register holds the address of the next instruction to execute?
Choose from the processor's internal components.
Correct answer: Program Counter (PC)
The PC register holds the memory address of the next instruction. It is automatically incremented during the fetch