Inside your computer
Every address contains 8-bits of data, a byte. Each bit can be
thought of as a switch which can be either on or off. A byte is
like a bank of 8-switches, where each switch can be on or off.
So 1Mbyte of memory consists of 1048576 (see Numbers and
computers) locations each containing one byte of data.
When installing expansion cards it is the first (bottom) Mbyte
of address space that is of most interest. The following diagram
shows how the bottom 1M of address space is used in your
computer. Diagrams like these are called memory maps, and
are a convenient way of representing processor address space.
A/10 XEN OWNER'S HANDBOOK
EXPANSION CARD ROM