Introduction

As the number of bits increases there are two important benefits.

More bits means that data can be processed in larger chunks which also means more accurately.

More bits means our system can point to or address a larger number of locations in physical memory.

32-bit systems could address (point to) 4 Gigabytes of memory in one go. 64-bit systems are now becoming more attractive because they can potentially address up to 4 billion times that many locations.

32 Bits

Computers, operating systems, or software programs capable of transferring data 32-bits at a time. With computer processors, (e.g. 80386, 80486, and Pentium) they were 32-bit processors, which means the processor were capable of working with 32 bit binary numbers (decimal number up to 4,294,967,295). Anything larger and the computer would need to break up the number into smaller pieces.

Example of 32 bit Operating systems: Windos 95 and Windows 2000

64 Bit

Replacement for the older x86 or 32-bit platform, 64-bit is a computer or software program that is capable of transferring 64-bits at a time. With respect to hardware, 64-bit is referencing the width of the registers on a computer's microprocessor or the computer bus; sometimes called WOW64 and x64.

Examples of 64-bit processors

AMD Opteron, Athlon 64, Turion 64, Sempron, Phenom, FX, and Fusion.

Intel Celeron and Pentium 4 processors since Prescott.

Intel Pentium Dual-Core, Core i3, Core i5, and Core i7 processors.

Computer can be divided into

three layers

Their are three layers with the processor

or CPU as the central or lowest layer

and the application as the outermost or

highest layer as shown below:

To run a 64-bit operating system you

need support from the lower level: the

64-bit CPU.

To run a 64-bit application you need

support from all lower levels: the 64-bit

OS and the 64-bit CPU.

What 32-bit and 64-bit combinations are

compatible and will work together?

The main reason that 32-bit will always

run on 64-bit is that the 64-bit

components have been designed to

work that way. So the newer 64-bit

systems are backward-compatible with

the 32-bit systems (which is the main

reason most of us haven't moved to 64-

bit software).

Virtualization

Some questions about 32-bit

and 64-bit systems Will a 64-bit CPU run a 32-bit program on a 64-bit

version of an OS?

Yes it will. 64-bit systems are backward-compatible with their 32-bit counterparts.

Will a 64-bit OS run a 32-bit application on a 64-bit processor?

Yes it will. Again, this is because of backward compatibility.

Can 64-bit applications contain 32-bit code?

Yes, many times 64-bit software will contain portions of 32-bit code.

Similarly 32-bit software (usually very old programs) can have some code in 16-bit which is why those 32-bit applications will usually fail to run properly on a 64-bit OS.

Can 16-bit applications or code run on 64-bit systems?

No, as we said previously. 16-bit code will NOT run on 64-bit OS because the designers did not provide backward-compatibility. This is one reason why some 32-bit programs will not work on 64-bit operating systems.

Can a 64-bit CPU with a 32-bit host OS run a virtual machine (VM) for a 64-bit guest OS?

Yes. It all depends upon the level of virtualization.

With software virtualization it is hardly likely to work, or if it does work it may be very slow.

Hardware virtualization will need to be supported by the CPU (e.g. with Intel-VT or AMD-V) and the BIOS.

Some questions about 32-

and 64-bit Windows

Can I run Windows 2000 and Windows XP on a 64-bit CPU, and use old software?

Yes, a 32-bit OS (Windows 2000 or XP) will run on a 64-bit processor. You should also be able to run older 32-bit software on a 64-bit OS.

How do find out if my system is 64-bit?

It is very simple, You have first right click on My Computer and the select properties, a window will open having information about the your system. Here you can see your processor is 32 bit or 64 bit.

Will my old device drivers work in Windows 64-bit

Many device drivers that work in Windows 32-bit will not work in Windows 64-bit.

How do I run 32-bit software once I have installed 64-bit Windows?

Windows 64-bit provides a 32-bit compatibility mode called WOW32 (Windows 32-bit on Windows 64-bit) that should run most if not all your applications. But 32-bit Windows applications are not automatically Windows 64-bit compatible. There are several reasons for this: they have 16-bit code.

How can I tell if my application is 32-

bit or 64-bit?

Windows installs your programs to these

folders on your system drive:

• '\Program Files' for 64-bit programs

• '\Program Files (x86)' for 32-bit programs

In Task Manager, 32-bit processes will

usually have a suffix of '*32' and 64-bit

processes will not.

AMD64 Features

The AMD64 architecture includes these features:

• Register Extensions (see Figure 1-1 on page 2):

- 8 additional general-purpose registers (GPRs).

- All 16 GPRs are 64 bits wide.

- 8 additional YMM/XMM registers.

- Uniform byte-register addressing for all GPRs.

- An instruction prefix (REX) accesses the extended registers.

• Long Mode (see Table 1-1 on page 2):

- Up to 64 bits ofvirtual address.

- 64-bit instruction pointer (RIP).

- Instruction-pointer-relative data-addressing mode.

- Flat address space.

operating systems and releases support

the x86-64 architecture in long mode

DragonFly BSD

FreeBSD

NetBSD

OpenBSD

DOS

Linux

OS X

Solaris

Windows