> ## Documentation Index > Fetch the complete documentation index at: https://docs.ionq.com/llms.txt > Use this file to discover all available pages before exploring further. # Backends > Trapped-ion QPU hardware and QPU software simulators Backends are the general term for the systems that process circuit jobs, both the physical quantum computers as well software simulators. For the purposes of quantum software development, hardware and software backends are functionally interchangeable assuming the job in question falls within the capabilities of both backends, and the data is processed in the same fashion in both cases. *** ## Backends ### Characterization Data A characterization is a snapshot of an IonQ QPU's performance at a moment in time. While our quantum computers are continuously calibrated moment to moment, we periodically take measurements of gate fidelities and other statistics. Current data is listed [in the UI](https://cloud.ionq.com/backends) *(Click on "Show Details" on a backend)*. Current and past characterizations are available [via the API](/api-reference/v0.3/characterizations/get-a-characterization), and the `last_updated` field refers to when the *characterization data* was last updated. ### Energy Reporting Hardware backends may report average power consumption in kilowatts (`kW`). This is a *broad* representation of the total power draw of the system and includes all *direct* components of it. ### Status The status of our systems can be found on [status.ionq.co](https://status.ionq.co/). The possible statuses are: * **Operational:** The system is meeting spec both in terms of job quality and throughput. * **Degraded:** The system is under-performing spec. The specific way it is under-performing will be noted on the status page. * **Under Maintenance:** The system is down while one or more components are under physical maintenance. *** ## Backend Types ### QPU Hardware | Type | Name | Availability | ID | Qubits | Location | | -------- | ------------------ | ------------ | ------------------------ | ------ | ------------------ | | Hardware | Forte Enterprise 1 | Available | `qpu.forte-enterprise-1` | 36 | Basel, Switzerland | | Hardware | Forte 1 | Available | `qpu.forte-1` | 36 | College Park, MD | | Hardware | Aria 1 | Retired | `qpu.aria-1` | 25 | College Park, MD | | Hardware | Aria 2 | Retired | `qpu.aria-2` | 25 | College Park, MD | | Hardware | Harmony | Retired | `qpu.harmony` | 11 | College Park, MD | ### Simulators Simulators provide a *simulation* of circuit execution, allowing a user to retrieve results similar to those they would get if they were run to run that same circuit on a hardware device. All of our simulators are hosted on Google Cloud and can be accessed with the backend name `simulator`. See our [Simulation with Noise Models](/guides/simulation-with-noise-models) guide for more information about our noise models and their usage. | Type | Name | Availability | Noise Model | Qubits | | --------- | ------------------------------ | ------------ | -------------------- | ------ | | Simulator | Ideal | Available | `ideal` (default) | 29 | | Simulator | Forte Noise Model | Available | `forte-1` | 29 | | Simulator | Forte Enterprise 1 Noise Model | Available | `forte-enterprise-1` | 29 | | Simulator | Aria 1 Noise Model | Available | `aria-1` | 25 | | Simulator | Aria 2 Noise Model | Available | `aria-2` | 25 | | Simulator | Harmony Noise Model | Retired | `harmony` | 11 | These qubit counts represent the upper limits for simulation jobs that can be submitted. Simulations approaching the ideal and Forte-class qubit limits may still fail, depending on the specific circuit.