Acrosser AR-B1894 - Manual (Page 38)

4.2.5Power Management Setup
4.2.5.1 ACPI Function
This function enables PCs to implement Power Management functions through
Operating System and also provides the opportunity to integrated the interface
for controlling power management and Plug-n-Play features on system devices.
4.2.5.2 ACPI Suspend Type
This item allows to set the ACPI suspend(sleep) mode instead of simply turning
off a computer. In S1 the computer consumes less power because HDDs and
some other devices are powered off, but CPU is still running and it requires its
fan to rotate. In S3 mode it's only RAM (system memory) that remains powered.