# Machines and targets

> The three Qsolve targets (CPU simulator, GPU simulator, quantum computer), when to use each, what they cost, and how to read availability on the Compute page.

Source: https://qsolve.omlabs.co/docs/use/machines-and-targets
Updated: 2026-11-12

Start on the CPU simulator. Use the GPU simulator when a circuit is too large for the CPU to finish in reasonable time. Use a quantum computer when you want to see how a workflow behaves on real hardware noise, and you accept a higher price, a wait in the queue and a noisier answer.

A **target** is the machine a run's quantum circuits execute on. 

## The three targets

| | CPU simulator | GPU simulator | Quantum computer |
|---|---|---|---|
| What it is | A noiseless quantum simulator on processors | A noiseless quantum simulator on graphics hardware | A real IBM quantum processor |
| Noise | None | None | Real hardware noise |
| Result | Exact up to sampling | Exact up to sampling | Noisy, mitigated by the workflow |
| Price | Lowest | Higher per run | By quantum seconds, the highest |
| Repeatable | Yes, with the same seed | Meant to be, with the same seed | No, devices drift |
| Best for | Small and medium circuits, first runs, checking your input | Large circuits | Seeing real-device behaviour |
| Hold | Equal to the quote | Equal to the quote | 1.5 times the quote |

Only the targets a workflow supports appear on its page. All Qsolve's own workflows list CPU, GPU and IBM, but an outside developer's workflow may support fewer.

## CPU simulator

The default and cheapest option. It simulates your circuits exactly, so you see the algorithm's behaviour without hardware noise. It is a good first check that the workflow handles your input and matches the baseline, and the headline accuracy on each workflow page is measured on it.

Simulation cost grows quickly with qubits. A workflow's page states its largest problem, for example 24 qubits for the optimisation workflows and 12 for each chemistry system.

## GPU simulator

The same noiseless simulation on graphics hardware, for larger circuits. It costs more per run, so it pays off only when the CPU run would be slow. If a run is predicted to exceed the workflow's time limit, switching target will not fix it. Reduce the problem or the settings that drive run time instead.

## Quantum computer

The card reads **IBM quantum computer**. Pick a **Device** from the chips (the form lists `ibm_fez`, `ibm_marrakesh`, `ibm_kingston` and `ibm_torino`) or type another device name. Expect these differences from a simulator:

- **Noise.** Results are noisier. Workflows apply error mitigation, and the run page shows raw and mitigated fidelity. See [Accuracy, fidelity and noise](/docs/use/accuracy-fidelity-and-noise).
- **Smaller circuits.** A workflow may reduce its circuits on hardware to keep them faithful. `generic-qubo`, for example, uses at most 2 layers on a quantum computer even if you ask for more.
- **Queueing.** Your jobs wait in the provider's queue. That wait does not count against the workflow's compute time limit, though it is bounded. If a run ends without its results, its queued provider jobs are cancelled, so you are not billed for results nobody reads.
- **No exact repeat.** Two runs of the same input can differ.
- **Cost.** Priced by quantum seconds, with a hold of 1.5 times the quote. See [Credits and pricing](/docs/use/credits-and-pricing).

Some workflows fall below their classical baseline on hardware. That is a property of today's devices, and the **On quantum hardware** table on the workflow page shows what to expect.

## The Compute page

**Machines** lists each target with a status and two counts: **Machines** (how many are connected) and **Waiting** (jobs in the queue). It refreshes every 10 seconds.

| Status | Meaning |
|---|---|
| Idle and ready | A machine is free. Your run starts as soon as it is sized |
| Starts on demand | No machine is running, but one starts when you submit. Allow a few minutes |
| No machine idle | Machines are busy. Your run waits in the queue |
| Coming soon | The target is not open yet and cannot be selected |

The quantum computer may not be open to every account yet. If its card is greyed out with "Coming soon" or "Not connected on this platform yet", use a simulator.