Most of the filesystem shared libraries ride on top of the Block I/O module.
The io-blk.so module also acts as a resource manager and exports a block-special file for each physical device. For a system with two hard disks the default files would be:
These files represent each raw disk and may be accessed using all the normal POSIX file primitives (open(), close(), read(), write(), lseek(), etc.). Although the io-blk module can support a 64-bit offset on seek, the driver interface is 32-bit, allowing access to 2-terabyte disks.