As the number of bits increases there are two
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
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
Example of 32 bit Operating systems:
Windos 95 and Windows 2000
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
Intel Pentium Dual-Core, Core i3, Core i5, and Core
Computer can be divided into
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
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-
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
Yes it will. Again, this is because of backward
Can 64-bit applications contain 32-bit code?
Yes, many times 64-bit software will contain portions of
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
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
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
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
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.
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
• 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