Chapter 15. solving boot problems.

when the computer has the data cable unplug, and error " hard disk not present". a subsecuent " press any key to reboot".

Chapter 2

How Many Bits at a time:  The CPU (Central Processing Unit), also called  a processor, partly determines which operating system can be installed. one major consideration is the number of bits a CPU processes at a time. All desktop and laptop processors sold today from either Intel or AMD can process 64 bits at a time, but older processors handled only 32 bits. To know which type of operating system to install, you need to be aware of three categories of processors currently used on desktop and laptop computers:

32 bit processors.
Processors that use underlying 32-bit processing with 64-bit instructions.
64-bit processors.