The Linux kernel accesses all devices including disk drives through the /dev filesystem.
In the past, IDE devices were /dev/hdX devices, while SCSI, SATA and USB mass storage devices were /dev/sdX devices. In recent kernels, which means recent distributions, even the IDE devices are now referred to with /dev/sdX device names.
That change is because the old IDE code has been dropped from the kernel for being too convoluted and difficult to maintain. The SCSI subsystem was well developed and clean so the drivers required for other device types have been added to the SCSI code base as modules.
Also, removable devices such as the Western Digital Storage Book are referenced as /dev/srX where the “r” stands for removable. It is unclear to me why a very large device such as the Storage Book which can have capacities from 250GB to 1TB are considered “removable” and the much smaller and more portable devices such as a USB thumb drive are not despite the fact that both are in reality removable.
Linux also supports software RAID at levels 0, 1 and 5. These Multi-Disk devices are accessed via /dev/mdX devices in the /dev partition.