32 and 64 Bit Operating Systems - What's the Difference? by Henrik Blunck

When talking about 8, 16, 32 and now even 64 bit operating systems, these relate to generations of operating systems. DOS was originally based upon 8 bits - giving a total of only 256 instructions. When the 80286 arrived, the first ability to break into 16 bits came, and with the arrival of 80386 and latter processors, 32 bits became possible. The main things to consider when talking of the number of bits are the following three elements:

A question of memory

The number of instructions

Backwards compatibility

Random Access Memory in 32 vs. 64 Bit

In an operating system that runs on a 32 bit processor, you can only address up to 4 gigabytes of memory. In order to address more than that you can use either a 64 bit processor or run a simulated memory system which could allow you to handle more than this 4 gigabyte level by addressing memory in more steps than one.

As you will have guessed already, running such a simulated system costs quite a bit of speed, so going for the 64 bit system is much better. When using Windows, you get a new maximum of 128 gigabytes being addressed directly. At the time of writing this, the limit for direct addressing is around 48 bits amounting to 256 tebibytes of data. We are only down to terabytes of hard drive space - being 1,024 gigabytes. So there are no worries about direct addressing potential with a real operating system.

The Number of Instructions In Either CPU

Just as you have a level of direct memory addressing, so you also have many more instructions when you can build up instructions consisting of 64 characters instead of only 32. We should remember that computers work in binary format. You only have 0 or 1 in a binary system - either shut off or turned on. That means you can have one instruction consisting of 32 0s, then 31 0s and 1 at the end etc.

In principle you don't need to know this as a normal computer user. But if you want to do some programming it is highly relevant to know about computer architechture to understand the anatomy of different CPUs.

Backwards Compatibility

One of the biggest problems with new versions of Windows has been the corporate strategy of backwards compatibility. You can't run the NTFS file format on a 16-bit CPU - and likewise running FAT-32 on a 64 bit processor wouldn't make any sense.

So, the success of Windows has come now that they realize they must produce versions that are directly relevant for your processor. That is the reason why you can today choose between a 32 bit or a 64 bit version of Windows 7. You live in exciting times in the sense that we are now breaking over the 32 bit barrier (of 4 gigabytes) into the fascinating world of 64 bits.

I hope this has helped you get a better overview of processors, memory addressing etc.