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Operating System Design
An operating system is a filter that keeps applications and other programs from directly interfacing with the computer hardware. Without the operating system present, all hardware components would have to have programs that would connect to the hardware. These drivers, would be five or six times larger than they are now.
Another aspect of the operating system that is important is how it interfaces with the hardware, especially the CPU. Most CPU's today are either 32 bit based or 64 bit based. The 32 bit operating system can run on either kind of CPU, but not efficiently. Moreover, many computer programs are not designed to take advantage of the processing power afforded by the operating system interface with the CPU. They work well, but not well enough.
See also: Windows 7 – 32-bit or 64-bit?
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32 Bit OS
What does it mean to have a 32 bit system? It means that there are 232 bits in the system or, more than 4 gigabytes of memory. From a physical standpoint RAM can only address and map that much. So if Windows 7 is running on a 32 bit platform, this means that it will be functional and map devices to the bit limit specifications of the CPU.
When the applications access the operating system the CPU will begin to implement the CPU that is unique to the program. It will see the common things that all programs see, but the amount of processing depends on the particulars of the program.
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64 Bit OS
Alternatively, a 64-bit version of Windows means that it will address 264 bits of memory or 18 quintillion (18 with 18 zeros) bits. That allows a lot of room for handling even the most intensive programs.
The 64 bit OS will only work with a 64 bit CPU because they are in sync regarding how processes and threads operate to produce the results of the program task. Larger bit sizes mean a large pipeline to handle the data. 32 bits can mean cycles per operation, whereas 64 bits will mean one cycle per operation. There can be a performance improvement by that standard.
Image Source: ArsTechnica
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While some of the theory involved in here may interest some, there are some questions that are on people's minds.
Will a 64 bit CPU run a standard, 32-bit program on a 64-bit version of an OS? Yes it will. 64 bit systems are backward compatible with their 32 bit system counterparts.
Will a 64-bit OS run a standard application on a 64 bit processor? Again, it will. This is due to the backward compatibility element.
Can I run W2K and WXP and Win7 on an 64 bit CPU, and use old software? Yes, a 32 bit OS (W2K, WXP, Win7) will run on a 64 bit processor. Also, old software will be able to run on a 64 bit OS, but it will not be efficient.
Finally, the difference between 64 bit and 32 bit Windows 7 is how the operating system coordinates the instruction set from programs before the CPU receives them. The CPU will process instructions in a cycle, from start to finish, and a 64 bit instruction is more efficient. For example, a 32 bit instruction may take two cycles, whereas a 64 bit instruction can perform the same operation in one cycle.