On boot, the InitGopBufferLogger driver is loaded. This driver does not require the heap allocator to be initialised. It is a standalone driver which does not rely on DeviceManager. After memory::init() is called, DeviceManager is called and initialises the IDT, and loads the APIC driver. The APIC driver initialises the ISA driver and the PCI driver which discover devices connected via their respective buses.
This operating system uses the tutorials at https://os.phil-opp.com/ as a base.