An x86 computer starts in real mode.
The X86 64 is considered to refer to the central processing unit for computers. The X86 64 predominantly supports both physical and virtual memory on computer systems.
Real mode: Real mode, also called real address mode, is an operating mode of 80286 and later x86-compatible CPUs. Real mode is characterized by a 20 bit segmented memory address space (giving just over 1 MB of addressable memory) and unlimited direct software access to all memory and I/O addresses and peripheral hardware. Real mode provides no support for memory protection, multitasking, or code privilege levels. 80186 CPUs and earlier, back to the original 8086, have only one operational mode, which is equivalent to real mode in later chips. All x86 CPUs in the 80286 series and later start in real mode when reset. Protected mode: In computing, protected mode, also called protected virtual address mode,[1] is an operational mode of x86-compatible central processing units (CPU). It allows system software to utilize features such as virtual memory, paging, safe multi-tasking, and other features designed to increase an operating system's control over application software. When a processor that supports x86 protected mode is powered on, it begins executing instructions in real mode, in order to maintain backwards compatibility with earlier x86 processors.Protected mode may only be entered after the system software sets up several descriptor tables and enables the Protection Enable (PE) bit in the Control Register 0 (CR0). Protected mode was first added to the x86 architecture in 1982, with the release of Intel's 80286 (286) processor, and later extended with the release of the 80386 (386) in 1985. Due to the enhancements added by protected mode, it has become widely adopted and has become the foundation for all subsequent enhancements to the x86 architecture. D.Ghosh Roy
Safe Mode is a good way to get the computer running so you can try and figure out why it won't boot up in normal mode. To boot your computer into safe mode do the following. When you turn the computer on start tapping F8 on the keyboard maybe once per second until you see the Safe Mode screen. http://www.onlinecomputertips.com/troubleshooting/safemode.html
Start the computer in 'Safe Mode'. Press the F8 key during boot up continuously until you get the option to start in safe mode.
Windows 2000, XP, and Vista do not have a "DOS mode." To start Windows 95 and 98 in MS-DOS mode, press F8 when the splash screen appears. Then select "Start computer in MS-DOS mode" from the list.
No.
x86 and x86-64 (x64) are not mutually exclusive. x86-64 is a superset of x86, with 64-bit instructions. Many people still run 32-bit (x86) applications and operating systems on 64-bit processors. The reverse is not possible, though; you can't run a 64-bit system on a processor that only supports 32-bit.
32-bit processors
how to shut down computer correctly??
it loads your computer with no hardware drivers so if there is a problem it will still start and then you can fix it.
Master boot record
start the computer in safe mode and roll back the driver