/sys/block - Describes block devices, such as hard drives, CD-ROMs, DVDs, and RAID and LVM devices. Examples: sda (first SATA or USB drive), dm-0 (first LVM device) and sr0 (first CD-ROM or DVD).
/sys/bus - Describes devices that are attached to the system bus.
/sys/bus/cpu - Describes the CPUs that are attached to the system. Look under /sys/bus/cpu/devices to see details about each CPU.