Skip to main content

Levels of abstraction in computer simulation

Short answer

Simulation abstraction levels range from circuit (transistors, accurate but slow) to workload (user jobs, fast but less detail). Intermediate levels include gate, register-transfer (RTL), instruction-set (ISA), and system (queuing model). Lower levels suit hardware design, higher levels suit performance analysis.

Explain the different level of abstraction for the simulation of computer system.

A computer system can be simulated at different levels of abstraction. A lower level shows more detail and is more accurate, but needs more data, effort and run time; a higher level hides detail and is faster. The level is selected by the purpose of the study.

Levels (from low to high)

LevelWhat is modelledTypical use
Circuit levelTransistors, voltages, currentsChip design, timing of circuits
Gate / logic levelLogic gates, flip-flops, signalsDigital logic verification
Register-transfer levelRegisters, ALU, buses, clock cyclesCPU design, control unit
Instruction-set levelInstructions, registers, memory contentsTesting programs, compilers, ISA
Component / system levelCPU, memory, disk, network as service centresPerformance of the whole system
Workload / application levelUsers, jobs, transactions, requestsCapacity planning, response time

Explanation

  1. Circuit and gate level: deterministic, built with HDL and electrical simulators. Not discrete-event in the queueing sense.
  2. Register-transfer level: models the data path cycle by cycle.
  3. Instruction level: models execution of machine instructions without the hardware detail.
  4. System level: uses queueing theory and discrete-event simulation. The CPU, memory and I/O devices are servers with queues; jobs are customers.
  5. Workload level: describes how users generate load (arrival rate, think time, job mix), and may drive a system-level model.
  detail, accuracy, run time   high
        ^   Circuit
        |   Gate
        |   Register transfer
        |   Instruction set
        |   System (queues)
        |   Workload             low

Choosing the level

  • Use a lower level when the design of hardware is being checked.
  • Use a higher level to compare scheduling, caching or the number of servers.
  • Mixed models may use detail for the component of interest and abstraction for others.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Simulation and Modeling chapter 10 questions →