Around 2003 the term 64-Bit computing was everywhere. Want to install Windows XP? Great! Do you want the 32-Bit disc or 64-Bit disc? Installing WinZip for your shiny new re-installed OS? Which version of installer do you want to download? 32 Bit or 64 Bit? I want the higher “version”, give me all those 64 Bits! Then, when you try to install the bigger & badder version of WinZip, your poor 32 Bit Operating System is not capable of running the 64 Bit installer. These were the questions and problems everybody was running into back in the day. Today, the term 64-Bit is ubiquitous as even smartphones are 64-Bit these days.
What does 64-Bit computing mean?
Everything in digital computers is around the bits 0 and 1. What that means is, you can represent everything from numbers to text in articles such as these, images of your childhood memories, songs of your favorite artist & hours of all those cat videos you adore using sequence of 0s and 1s.
Here are some examples of binary representations:-
|Et tu, Brute?||01000101011101000010000001110100011101010010110000100000010000100111001001110101011101000110010100111111|
Each of these 0s and 1s are called bits. 8 consecutive bits form a byte. 1024 (2 to the power of 10) bytes make a Kilobyte. 1024 Kilobytes make a Megabyte. 1024 Megabytes make a.. you know the math.
For these bits to be useful, they need to be stored in the memory. Memory can be either primary or secondary. Secondary memory is your permanent storage like the Hard Disk Drive or the fancy new Solid State Drive. If you have been living under a rock, it could also be a CD/DVD drive or the floppy disks from the stone age. Primary memory on the other hand is volatile and gets wiped out on system shutdown/reboot.
These days it is quite common to have primary memory (RAMs) in the range of 8 to 16 GB on PCs and Laptops. Heck, even some crazy Android smartphones ship with 8 Gigs of RAM. Why a phone needs that much amount of memory is a different topic all together.
Each memory location in the RAM has a unique address and all of these addresses have a unique number assigned to them. The CPU uses these memory locations to store and retrieve the bits of data. The smallest amount of data that can be stored is a byte. Although, the fact that a byte is made up of bits means we can still refer to it all as bits. You just have to store 8 of them together at the very minimum.
The maximum amount of RAM that the CPU can read/write from is governed by whether the CPU is 32-Bit, 64-Bit or the “soon” to be 128-Bit. To address each memory location for reading and writing, the CPU needs to keep track of these addresses. This activity requires memory too and this is what is implied by whether your CPU is 32-Bit or 64-Bit. A 32-Bit CPU can support a maximum of 2 ^ 32 memory i.e 4 GB. That is the theoretical limit, though. On Windows, the practical limit was around 3.2 GB. But, there are some 32-Bit Linux kernels that support more than 4 GB of RAM using something called Physical Address Extension (PAE).
So, now that you know what 64-Bit computing is. What are/were the implications of this? Well, first of all, if your system had less than 3.2 GB of RAM there was no point in having a 64-Bit processor. Without having a 64-Bit CPU you could not even install a 64 Bit Operating System.
On Windows, you would have to use a 64-Bit OS if you wanted to make use of RAM beyond 3.2 GB. On Linux, like mentioned before there were ways to circumvent that. But, generally speaking you would go for a 64-Bit Kernel for RAM greater than 4 Gigs.
The next is software compatibility. Programs can be compiled to either 32-Bit or 64-Bit. A 32 Bit machine cannot run a 64 Bit program under any circumstances. While, a 64 Bit machine can run 32 Bit programs. On Windows, the WoW64 subsystem allowed 32-bit programs to run on a 64 Bit OS, albeit at a small performance cost.
The rule of thumb was, if you could find a 64-Bit version of the software, use that on your 64-Bit machine. If not, keep using the 32-Bit version of the software. In the early days, some folks could not even install the 64-Bit OS on their brand new 64 Bit CPU because some application they could not live without did not have a 64 Bit version. Some could not even run on a 64 Bit machine using WoW64 (think anti-virus or other low level software & games).
One thing to note though, is that even a 32-Bit OS can support disks (secondary memory) way greater than 4 GBs.
Putting it all together
So summing it all up. 64 Bit computing implies that you can utilize primary memory greater than 4 GB on your computer. It also means that you possibly have individual programs that require more than 4 Gigs of RAM.