2^64 Bits In Gigabytes

[Marie Ota]

Secondmotherboards have their own limits on how much RAM they can support, both physically and logically. Physically, there are only going to be so many slots available for RAM. As for the "logical" limits, I don't fully understand why this is still the case for x86-64 (the memory controller having long since been migrated into the CPU itself), but there it is. Presumably corners are being cut on address lines to save a few bucks in design and manufacturing.

Third, an operating system may have internal limitations as to how much RAM it can efficiently support. In part, this is actually to prevent needing overly large data structures to keep track of usage for memory that isn't really there. Last I checked, Linux allows 128TB of virtual address space per process on x86-64, and can theoretically support 64TB of physical RAM.

Fourth, some operating systems (e.g. Windows) will artificially limit how much RAM can be used as a tactic to make users upgrade to more expensive versions if they want more RAM (Windows 7 Starter is limited to 2GB, Home Basic to 8, Home Premium to 16, and Professional and above are 192GB, and Windows Server releases have far higher limits).

A 64-bit machine should be able to address up to 264 addressable units (in architectures designed over the last few decades, addressable units are invariably bytes, a.k.a. octets). If you define a "gigabyte" as 230 addressable units, then yes, 234 gigabytes would be another way to express the same count.

What Google search produced those ridiculous tiny results? Maybe the page you found was talking about the amounts of RAM you can buy in reasonably cheap boxes of a certain model -- you can most definitely have much more RAM (all addressable, of course) even in boxes that are far from being very costly.

Operating systems most definitely can and do restrict the amount of addressable memory (for example, they can do so by limiting the size of page tables, perhaps to some configurable maximum that can be set by recompiling or otherwise reconfiguring the OS -- it's hard to be more specific without focusing on some specific group of OSs).

If you're running an hungry CPU intensive application that's also intensive on other hardware like your hard disk then you best seriously consider a second CPU, in a completely separate machine. For example, running an database application and email server both on separate machines.

For a single machine with loads of memory it's better but not that brilliant if you have multiple applications running on the same system - regardless with the amount of memory installed. This is the very reason why big companies use not only 64bit architecture to address more memory but they also load balance the whole lot with two or more servers.

My advice is to save your bucks on memory and purchase a second server and then load balance the two. It's a lot simpler plus - once you get into the grips of it - it's easy to expand when you need more processing power and speed.

Since the whole market is going 64bit in terms of both hardware and software I would advise to go 64bit for the long term but, forget the idea of squashing all onto one single machine with bucket loads of memory because you'll be disappointed.

That means 64-bit processor can take 264 B = 16 EB, but I can't how addresses that locked for reversed used. so we can say 64-bit processor take more than 1 EB. and this specification does not depend of what the OS the PC used or what its model.

Taking an Intel or AMD CPU as an example, there are several limitations to both physical memory and virtual memory. Other people have talked about hardware pin-out and motherboard limitations, but there are also internal limitations.

Internal to the CPU, the CPU caches also have a limitation on the number of physical address bits they store, since each additional address bit eats more transistors to the cache tag. DRAM controller pin limitations are not necessarily the final word, since memory can also be addressed through DMI links.

Do you think that we will someday need more memory than can be addressed with 64 bits?2^64 is 18,446,744,073,709,551,616. That's 17,179,869,184 gigabytes.

Suppose you had some kind of memory storage device which could store 1 gigabyte in a 1 millimeter by 1 millimeter square. Then your whole system would occupy a field 130 meters by 130 meters. Or you could go 3-D -- suppose you have a 1 GB device 1 millimeter by 1 millimeter by 1 millimeter. Then you would need a volume 2.5 meters by 2.5 meters by 2.5 meters to hold enough of these devices to store 2^64 bytes.And what would you store in there? Let me put it another way -- what's your max bandwidth? How many bytes of data can you meaningfully produce or consume in a second? Let's say that you will someday produce and/or consume 1 GB per second, and you want to store all of this stuff for possible later use. Then this device that you have can store enough of this data for 544 year's worth of uninterrupted, non-repeating production/consumption.Maybe corporations, AIs, or neo-humans will have use for such amounts of memory, but I don't think that humans will!

to post comments 2^64 bytes is enough for any human Posted Apr 15, 2004 17:59 UTC (Thu) by fjf33 (guest, #5768) [Link] (4 responses)

I'm always suspicious of these statements. Throughout history, people have been smart and imaginative. Though I was not talking to people about memory sizes in those days, I'm sure anyone who thought about it seriously realized we would need 1MB of memory in a computer.They quite possibly didn't think we'd ever be able to get it, but that's a whole different discussion.I guess we could put it another way: Nobody thought in the future we would need 20 bit addresses. (Because we'd never be able to get 1MB of memory behind a single CPU). 2^64 bytes is enough for any human Posted Apr 20, 2004 16:47 UTC (Tue) by zooko (guest, #2589) [Link] (2 responses)

I've seen discussions of this number before, but I don't remember the result. But I seem to recall it being less than 2^128; thus, a 128-bit address space is good enough for anyone. Really.There are other arguments based on thermodynamics limiting the complexity of a computer. Google for discussions of thermodynamics and reversible vs. irreversible computers and you'll see what I mean. 2^64 bytes is enough for any human Posted Apr 15, 2004 18:26 UTC (Thu) by tjc (guest, #137) [Link] (1 responses)

And just think how long it would take for the POST to count all that! :-) You'd need a pretty fast CPU too.. 2^64 bytes is enough for any human Posted Apr 16, 2004 3:29 UTC (Fri) by wolfrider (guest, #3105) [Link]

I do, but the question you've answered is really, will we someday need more than 2^64 bytes of memory in a computer like the ones we have today?You've made an excellent argument that the answer to that question is no.On the other hand, I'm sure some day computers will be structured differently, and we will most likely be addressing memory larger than what fits on a motherboard, or even in one building. There is definitely more than 2^64 bytes of information to be stored in the world. We'll struggle for a while with all the usual stopgaps -- paging, multilevel addressing, and such. But eventually we'll break down and get more than 64 bits of address space and go through a transition much like the 32/64 one. 2^64 bytes is enough for any human Posted Jan 18, 2011 10:24 UTC (Tue) by stealthpaladin (guest, #72424) [Link] (1 responses)

Some time around 2009 Google CEO estimates 500 million terabytes of data attributed to the internet.

So by now, we could probably use a 2^64 computer to hold 2.x backups of the internet =P Which could have it's uses =P

as goes 2^128 and this idea

"Clearly you can't do better than (or even as well as) harnessing the largest set of good quantum numbers of every particle in the universe. (Your computer has to be in the universe!) "

Well there are ways to take a few values (say 8 for example) and based on these achieve further resolution than 8 (say 256 for example =P) Really there are many techniques which provide more resolution for processing and storage than their components, so I think identifying the whole universe may not be so impossible really.

I also think of the whole,... leaf in a pond thing. There's an idea that if you can *fully* define and understand one particle on the leaf then you can access the info of the entire pond. Perhaps with 2^128 we could define one proton so well that everything else is just implied lol.

2^64 bytes is enough for any human Posted Jan 18, 2011 10:28 UTC (Tue) by stealthpaladin (guest, #72424) [Link]

The size of information in the computer is measured in kilobytes, megabytes, gigabytes, and terabytes. In this section, we'll look at common sizes you would see in real life and learn how to reason about various numbers of bytes.Kilobyte or KBKilobyte KB - about 1 thousand bytesAs we know, 1 byte is one typed character

- see below for why the phrase "about 1 thousand" is required hereAn email without images is about 2 KBA five page paper might be 100 KBText is compact, requiring few bytes compared to images or sound or videoe.g. 23,000 bytes is about 23 KBOne kilobyte (KB) is a collection of about 1000 bytes. A page of ordinary Roman alphabetic text takes about 2 kilobytes to store (about one byte per letter). A typical short email would also take up just 1 or 2 kilobytes. Text is one of the most naturally compact types of data at about one byte required to store each letter. In non-roman alphabets, such as Mandarin, the storage takes up 2 or 4 bytes per "letter" which is still pretty compact compared to audio and images.Megabyte or MBMegabyte (MB) - about 1 million bytesaka about 1000 KBMP3 audio is about 1 megabyte per minuteA high quality digital picture is about 2-5 megabytese.g. 45,400 KB is 45.4 MBOne megabyte is about 1 million bytes (or about 1000 kilobytes). An MP3 audio file of a few minutes or a 10 million pixel image from a digital camera would typically take up few megabytes. The rule of thumb for MP3 audio is that 1 minute of audio takes up about 1 megabyte. Audio and image and video data typically stored in "compressed" form, MP3 being an example. We'll talk about how compression works later. A data CD disk stores about 700 MB. The audio on a CD is not compressed, which is why it takes so much more space than the MP3. The series of bits are represented as spiral path of tiny pits in the silver material in the disk. Imagine that each pit is interpreted as a 0, and the lack of a pit is a 1 as the spiral sequence is read. Fun fact: the whole spiral on a CD is over 5km long.Math - You Try It 2,000,000 bytes is about how many MB?Show Solution2,000,000 bytes = 2 MB 23,000 KB is about how many MB?Show Solution23,000 KB = 23 MB (1000 KB = 1 MB) 500 KB is about how many MB?Show Solution500 KB = 0.5 MBGigabyte or GBGigabyte GB = about a billion bytesaka about 1000 MBGB is a common unit for modern hardwaree.g. 4000 MB = 4 GBAn ordinary computer might have:

-4 GB or RAM

-256 GB of persistent storageA DVD disk has a capacity 4.7GB (single layer)-Figure 2 GB per hour of video (varies greatly)A flash drive might hold 32 GBA hard drive might hold 750 GBOne gigabyte (GB) is about 1 billion bytes, or 1 thousand megabytes. A computer might have 4 GB of RAM. A flash memory card used in a camera might store 16 GB. A DVD movie is roughly 4-8 GB.Math - You Try ItHow many GB is 4,000,000,000 bytes?Show Solution4 billion bytes = 4 GBSay you have many 5 MB JPEG images. How many fit on a 16 GB flash drive?Show Solution(convert everything to MB)

16 GB is 16,000 MB

16,000 / 5 = 3,200Terabyte or TBOne terabyte (TB) is about 1000 gigabytes, or roughly 1 trillion bytes. You can buy 4 TB hard drives today, so we are beginning the time when this term comes in to common use. Gigabyte used to be an exotic term too, until Moore's law made it common.Gigahertz - Speed, not BytesOne gigahertz is 1 billion cycles per second (a megahertz is a million cycles per second). Gigahertz is a measure of speed, very roughly the rate that at a CPU can do its simplest operation per second. Gigahertz does not precisely tell you how quickly a CPU gets work done, but it is roughly correlated. Higher gigahertz CPUs also tend to be more expensive to produce and they use more power (and as a result give off more heat) - a challenge for putting fast CPUs in small devices like phones. The ARM company is famous for producing chips that are very productive with minimal power and heat. Almost all cell phones currently use ARM CPUs.Kilobyte / Megabyte / Gigabyte Word ProblemsYou should be comfortable doing simple arithmetic to figure MB / GB sizes, just as you should be able to do basic computations with second, miles, kilos and so forth.Basic plan: before adding measures X and Y, convert them to be in the same units.Word ProblemsSolutionAlice has 600 MB of data. Bob has 2000 MB of data. Will it all fit on Alice's 4 GB thumb drive?showYes it fits: 600 MB + 2000 MB is 2600 MB. 2600 MB is 2.6 GB, so it will fit on the 4 GB drive no problem. Equivalently we could say that the 4 GB drive has space for 4000 MB.Alice has 100 small images, each of which is 500 KB. How much space do they take up overall in MB?show100 times 500 KB is 50000 KB, which is 50 MB.Your ghost hunting group is recording the sound inside a haunted Stanford classroom for 20 hours as MP3 audio files. About how much data will that be, expressed in GB?showMP3 audio takes up about 1 MB per minute. 20 hours, 60 minutes/hour, 20 * 60 yields 1200 minutes. So that's about 1200 MB, which is 1.2 GB.

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