# Investigating storage, disks and volumes
### Disk
The term disk refers to the physical storage device of a computer. However, there are instances where it can represent a logical disk, which spans across one or more physical disks. For example, with a redundant array of independent disks (RAID) configuration, you combine multiple physical disks to form a single logical disk, providing increased performance, redundancy or both.
**Windows**
In the **Disk Management** application, the system calls physical drives **disks** and labels them as `Disk 0`, `Disk 1`, ... Under **This PC**, the system assigns these storage devices drive letters (`C:`, `D:`, ...).
These devices can vary in type, including local disks, USB drives or virtual disks.
**macOS**
In the **Disk Utility** application, the system calls physical drives **media** and they appear as top-level entries. The system classifies them as internal or external and labels them as `disk0`, `disk1`, ...
Using the `diskutil list` command, you can display all devices as `/dev/disk0`, `/dev/disk1`, ...
### Volume
Volume refers to a storage unit within a disk that organizes and manages data. It functions as a logical partition and can be formatted with a file system, allowing users to store and access files. Although a single disk can contain multiple volumes, each volume operates independently, providing additional flexibility and organization to the storage system.
**Windows**
On Windows, in the **Disk Management** application, the system lists volumes under **Volume.**
**macOS**
In the **Disk Utility** application, the system displays volumes under the media they belong to.
Using the `diskutil list` command in macOS shows volumes beneath their respective disk drives, with identifiers like `/dev/disk0s1`, `/dev/disk0s2`, ...
### NQL examples List the system drive (volume/partition) free space on devices.
```
devices during past 7d
| include volumes
| where system == true
| compute system_drive_free_space = capacity.sum() * (1 - usage.sum())
| list device.name, system_drive_free_space
```
List the system drive usage on devices.
```
devices during past 7d
| include device_performance.events during past 7d
| compute system_drive_used = event.system_drive_usage.avg()
| list device.name, system_drive_used
| sort system_drive_used desc
```
List devices with less than 5GB available on the system drive.
```
devices during past 7d
| include volumes
| where system == true
| compute system_drive_free_space = capacity.sum() * (1 - usage.sum())
| where system_drive_free_space < 5GB
| list device.name, system_drive_free_space
```
List a summary of the disks and volume of devices.
```
devices during past 7d
| list device.name, disks, volumes
```
List all disks from all devices with their size, bootable status and type (SSD or HDD).
```
disks during past 7d
| list device.name, name, is_bootable, capacity , type
```
**Working with custom fields**
If you use a specific NQL query often, consider creating a custom field.
Find more information about custom fields on the [Custom fields management](/platform/~/changes/Sh4xqs4GDClkDKT9Hvux/user-guide/administration/content-management/custom-fields-management.md) page.
Using a custom field in an NQL query to list devices with less than 5GB available on the system drive.
```
devices
| where #system_drive_free_space < 5GB
| list device.name, #system_drive_free_space
```
---
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