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# What Is a Bit, and Why Are Some 32 and Others 64?

Gary can you please explain to me, or point me towards a video that will explain the difference between a “32 bit”, and a “64 bit”…”something”?
What is a bit? what is 32 & 64.

These two things keep popping up in my life and I figure better to learn them, than to avoid this any longer. Which is what I’ve been doing.

This morning I received a link for a bundle of free macros for Affinity Photo for HDR. But, it said this is for 32 bit only….no idea what that means.
—–
Greg

### Comments: 2 Responses to “What Is a Bit, and Why Are Some 32 and Others 64?”

3 years ago

A bit is the smallest unit of memory in a computer. It can hold only one value, on or off, also represented as 0 or 1. So computers use a number system based on the bit, known as base-2. We usually use numbers in base-10 which has digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. But base-2 just has 0 and 1.

In base-10, we count from 0 to 9, and then the next number is 10. In base-2, you go 0, 1, and then 10. A "10" in base-2 is the same as the number "2" in base-10. So 0, 1, 2, 3, 4, 5 would be written in base-2 as 0, 1, 10, 11, 100, 101.

So an 8-digit base-2 number can range from 00000000 to 11111111 which is the equivalent to 0 to 255 in base-10. An 8-digit base-2 number can also be called an "8-bit number." So a "32-bit number" would be something with 32 digits in it. From 32 zeros to 32 ones. That would represent the base-10 numbers from 0 to 4,294,967,295 (4 billion). A 64-bit number would be able to go up to 18,446,744,073,709,551,615 (18 billion billion).

So how does this apply to apps? When apps do things they use numbers. A computer program, or app, is basically just a long list of numbers that manipulates other long lists of numbers. So what is the largest number than an app can use? If it is a 32-bit app, then it is 4 billion. If it is a 64-bit app, then the largest numbers is 18 billion billion. That doesn't mean a 32-bit app can't use larger numbers. It just takes more units of memory to do so. So a 64-bit app can handle larger numbers faster than a 32-bit app.

But the operating system (macOS) and the app must agree on whether they are using 32-bit or 64-bit numbers. The early versions of OS X were 32-bit and only 32-bit apps existed. Starting around OS X Leopard, the operating system supported both 32-bit and 64-bit apps and developers could build their apps either way. Starting with macOS Catalina, only 64-bit apps are supported. This means macOS no longer has to include old code that enabled old 32-bit apps.

When an app says it is for "32-bit only" that means it will only work on macOS version Mojave or earlier. Chances are that is an old version of the app that hasn't been updated. Since around 2016 Apple has encouraged all developers to make their apps 64-bit. Even before that, many of them did. And in the last few years any app needed to be 64-bit to even get into the Mac App Store.

Greg
3 years ago

WOW! Thanks so much!