Buses
A bus is a series of lines that connect the processor to another part of the computer's architecture, such as cache memory or main memory.
Address bus
The address bus is uni-directional
It is concerned with passing an address one way, from the CPU to RAM.
The sole purpose of an address bus is to identify the address of the location in cache or main memory that is to be read from or written to. Each location in memory will have its own unique address, this is known as addressability.
Data bus
The data bus is bi-directional.
It can carry data to main memory from the processor and vice versa.
The data bus will transfer data to/from the address that is held on the address bus.
The amount of data that can be carried by the data bus depends on the word size. Word size describes the width of the data bus. At the moment new processors will usually have a word size of 8 bytes (64 bits), allowing for 64 bits to be transferred during each cycle.