System-information messages are sent by Windows when an application or a user makes a system-wide change that affects other applications. The following list briefly describes each system-information message:
| Message | Description | |
| WM_COMPACTING | Sent to all top-level windows when Windows requires too much system time compacting memory, indicating that system memory is low. | |
| WM_DEVMODECHANGE | Sent to all top-level windows when the user changes device-mode settings. | |
| WM_FONTCHANGE | Sent when the pool of font resources changes. | |
| WM_PALETTECHANGED | Notifies all windows that the system color palette has changed. | |
| WM_SPOOLERSTATUS | Sent from Print Manager whenever a job is added to or removed from the Print Manager queue. | |
| WM_SYSCOLORCHANGE | Sent to all top-level windows when a change is made in the system color setting. | |
| WM_TIMECHANGE | Sent when an application makes a change or set of changes to the system time. | |
| WM_WININICHANGE | Sent when the Windows initialization file, WIN.INI, changes. |