Most of the filesystem shared libraries ride on top of the Block I/O module.

The 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:

First hard disk.
Second hard disk.

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.