# Nuvolos Compute Units (NCUs)

## CU definition

The Nuvolos Compute Unit (CU) is the computational unit for regular (non-HPC) applications run by users, and is the main unit of account for Nuvolos subscriptions.

In terms of computational resources, a CU consists of 1 virtual CPU (vCPU), 4 GB of RAM, and adequate temporary storage to run a particular application.

{% hint style="info" %}
A **vCPU** (virtual CPU) is a share of a physical processor core allocated to your application by the cloud infrastructure. It behaves like a dedicated CPU core for scheduling and running your code, but multiple vCPUs from different users may share the same physical hardware. A 4 CU application, for example, can use up to 4 vCPUs — roughly equivalent to a quad-core laptop processor.
{% endhint %}

## CU consumption of applications

Every time a user starts an application, a corresponding number of CUs are checked out from the service. The following default values apply:

* Applications in teaching spaces consume a single CU.
* Applications in research and dataset spaces consume 4 CUs.

Space administrators can change the CU consumption of applications. In research spaces, even Instance Editors can change the CU settings of applications to allow for seamless collaboration. To learn how to resize an application, see [Changing application resources](/features/applications/application-resources.md#changing-application-resources).

{% hint style="info" %}
Application sizes can be changed at any time as long as the project is active. Running applications must be restarted for the new size to take effect. Beyond the included sizes, credit-based sizes with GPUs and larger configurations are available — see [Application resources](/features/applications/application-resources.md) for the full details.
{% endhint %}

## CU limits of a resource pool

Each [resource pool](/pricing-and-billing/resource-pools-and-budgets.md) has a certain number of CUs available for consecutive use over the subscription period. To review your current utilisation, see [CU limits and capacities](/administration/monitoring-resource-usage/ncu-limits-and-capacities.md).

{% hint style="info" %}
When you reach your CU limit, applications continue to run without interruption as long as you maintain a positive credit balance. For options when approaching or exceeding capacity, see [CU limits and capacities — what happens when you reach your limit](/administration/monitoring-resource-usage/ncu-limits-and-capacities.md#what-happens-when-you-reach-your-limit).
{% endhint %}


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