What is 64-bit?

Have you noticed that the technical specifications for computing technology always seem to be numbers that double after a while? This has particularly been true of numbers with the word “bit” after them. 8-bit. 16-bit. 32-bit. And now, yes, 64-bit is the latest buzz. But if you’re a normal person (not a computer person), what does this mean?

One of my colleagues (Ed) sent me a link to this short article that loosely explains what 64-bit means to you, the normal person: What the iPhone 5s ’64-bit’ processor means, in plain English. I particularly like the library and book analogy. While I see from the comments that the true technophiles object to the explanation, I’m still going to call it good enough for the normal person. By passing it along, I hope it’s helpful to you or someone you know.

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2 Responses to What is 64-bit?

  1. Danny says:

    Resident technophile here. Yes, I disagree with that analogy. πŸ˜‰ The explanation in that article is why a 64-bit bus would be better than a 32-bit bus. And it’s a good analogy of that difference. The main problem is that bus width is not the important part of what changed. πŸ™‚ The “number of bits” in a processor refers to the size of an address that it can talk to; it’d be more like the number of shelves in the library. A better analogy, IMHO, would involve a telephone. Say the CPU is participating on a game show. When it doesn’t have the information it needs, it can phone a friend to get that information. The phone numbers for the CPU’s friends are in a rolodex. But the rolodex only has a fixed number of cards inside, and that’s all the friends it can possibly call. A 32-bit processor only has enough cards to call 2^32 friends as most. That’s about about 4 billion friends (which is about 4GB of RAM). However, a 64-bit processor can keep a whole lot more phone numbers in its rolodex. At first, you think “well, it’s just 2x more”. No. 2^64 is theoretically about 16 exabytes. And “exabyte” is so big that most people have no idea if that’s even a real word (the relevant sequence is kilobyte, megabyte, gigabyte, terabyte, petabyte, exabyte). It’s like having 4 billion rolodexes that could hold 4 billion numbers each. It’s a whole lot more phone numbers than people will be needing in the near future. πŸ™‚

    Perhaps rather than a rolodex, it’s a card catalog with a fixed number of drawers. Or some other technology with limited storage capability. Whatever.

    Anyway, why is it important to be able to use more than 4GB of RAM? I mean, hard drives are literally thousands of times larger. I can buy a 4 terabyte hard drive! Who cares about puny ol’ RAM? Well, the CPU getting information from RAM is fast – like making a phone call. But if the information isn’t available in RAM; it has to go to the hard drive. That’s more like writing a letter, but like a letter to someone in the same state (it’s a big state; maybe Texas, and we’re probably using priority mail rather than regular first class). Fetching information from the Internet is like writing a letter to someone in a differnet country. The CPU’s L1 cache would be like asking your spouse who’s sitting next to you on the couch, the L2 cache would be like shouting up the stairs to your son who just won’t move out even though college was over years ago, and L3 cache would be yelling out the window at your neighbor who bumped his head earlier this afternoon and is still a tad groggy. But that’s dragging this analogy significantly farther than it needs to be drug. The salient pont here is that CPU bittedness (which really should be a word, but probably isn’t) refers to how much RAM can be uniquely addressed, not necesarily how fast it can be fetched. It’s the number of license plates available in the state, not how many lanes are on the road. πŸ˜‰

    • Ben K says:

      Thanks for the thoughtful response, Danny! I really like the “number of license plates available in the state vs. the number of lanes on the road” analogy. We might have to work that into a video so that there’s a better analogy-based explanation out there for this 32 vs. 64 bit question.

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