# Gigabytes, gigabits, gibibytes, etc.
**URL:** https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934
**Category:** Factual Questions
**Created:** [April 20, 2007, 1:55pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934 "2007-04-20T13:55:21Z")
**Posts on this page:** 14
**Page:** 1
### Author:  [@ReuvenB](https://boards.straightdope.com/u/ReuvenB)
#### Post date: [April 20, 2007, 1:55pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/1 "2007-04-20T13:55:21Z")
After looking at hard drives to add to my computer (running out of space), it occurred to me that while I seem to have been told that a gigabyte is 1024 (2[sup]10[/sup]) megabytes, someone has told hard drive manufacturers differently. A friend of mine pointed out that he believes they’re defining one gigabyte as 1000 megabytes or perhaps just 1,000,000,000 bytes. What’s the correct definition? Why do hard drive manufacturers define it differently than I do? Which media use the same definition that I do, and which use the mutant numbering scheme of hard drives? Which do flash media use? DVDs? HD-DVD? Blu-Ray?
And most importantly, why can’t everyone just agree on a standard?
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### Author:  [@Scuba\_Ben](https://boards.straightdope.com/u/Scuba_Ben)
#### Post date: [April 20, 2007, 2:10pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/2 "2007-04-20T14:10:53Z")
I happened to come across this the other day: In storage media, capacities are expressed in powers of ten. In the rest of the computing world, it’s in powers of 2[sup]10[/sup]. So what you and I as tech folk call a gigabyte (2[sup]30[/sup] bytes) is apparantly properly called a gigabibyte (GiB).
However, I have only read this on Wikipedia. It cites IEEE 1541 as a standard defining the engineering prefixes for binary values; I have yet to read the IEEE standard.
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### Author:  [@Keeve](https://boards.straightdope.com/u/Keeve)
#### Post date: [April 20, 2007, 2:21pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/3 "2007-04-20T14:21:17Z")
[QUOTE=XWalrus2]
Why do hard drive manufacturers define it differently than I do?
[/QUOTE]
Marketing. It’s all marketing. Like other terms such as “low-fat cookies” or “long-life lightbulbs”, these terms can mean anything that the advertisers want them to mean. Eventually, some gov’t agency or industry group will set some sort of standard meaning, but until then it is every man for himself.
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### Author:  [@awldune](https://boards.straightdope.com/u/awldune)
#### Post date: [April 20, 2007, 2:36pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/4 "2007-04-20T14:36:21Z")
[http://en.wikipedia.org/wiki/Binary\_prefix](http://en.wikipedia.org/wiki/Binary_prefix)
> **[Hard disk drive](https://en.wikipedia.org/wiki/Hard_disk#Capacity_measurements)**
>
> A hard disk drive (HDD), hard disk, hard drive, or fixed disk,\[b\] is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored and retri
Basically, the 1024 = kilo convention is non-standard and hard drive capacities follow the official SI (International System) standard. CD media and RAM are two formats that use the 1024 measurement, but most other hardware uses decimals.
Given the popular understanding of 1024 = kilo, it is arguable for hard drives to adopt that convention, but the SI standard gives them a decent excuse for providing you a little less.
The SI standard prefix for multiples of 1024 is kibi, mebi, gibi, etc. No one seems to want to use them, and I don’t blame them.
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### Author:  [@Polycarp](https://boards.straightdope.com/u/Polycarp)
#### Post date: [April 20, 2007, 2:51pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/5 "2007-04-20T14:51:04Z")
Actual SI nomenclature is decimal: kilo = 1000, mega = 1 million, giga = 1 billion.
As **Scuba Ben** notes, in many but not all aspects of electronic information storage, the related forms in binary are the default:
Kilo = 2[sup]10[/sup] = 1,024
Mega = 2[sup]20[/sup] = 1,048,576
Giga = 2[sup]30[/sup] = 1,073,741,824
These are used because they are powers of 2, hence logical increments in binary usage, which approximate the related powers of 10, for which there are common SI prefixes.
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### Author:  [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)
#### Post date: [April 20, 2007, 2:52pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/6 "2007-04-20T14:52:09Z")
[QUOTE=Scuba\_Ben]
I have yet to read the IEEE standard.
[/QUOTE]
It’s very short, just a few lines more than two pages. It does distinguish between the gibi- prefix as gigabinary or 2[sup]1000[/sup] versus the giga- which is 10[sup]9[/sup]. The following text is how the standard closes:
> [@IEEE 1541](#):
>
> Example 1:
> The common 90 mm diskette, as formatted for PC use, is usually advertised as containing 1.44 megabytes.
>
> It is actually formatted for 1440 kibibytes, and the “mega” in this application is neither a proper SI prefix nor a binary prefix. The resulting hybrid “megabyte” is equal to 10[sup]3[/sup] ×2[sup]10[/sup] bytes.
>
> Example 2:
> The following “frequently asked question” appears in an instruction manual widely distributed in 1999:
>
> Q: The formatted capacity of my hard drive seems smaller than what was ordered. Why?
>
> A: Your operating system assumes that 1 MB equals 1 048 576 bytes. Drive manufacturers consider 1 MB as equal to 1 000 000 bytes. Thus, if the drive is advertised as 6.4 gigabytes (6 400 000 000 bytes), the operating system sees it as approximately 6.1 GB [(6 400 000 000)/(1 048 576 000) = 6.1035…].
>
> Note that in this example, the PC vendor creates a hybrid “gigabyte” that is equal to 10[sup]3[/sup] × 2[sup]20[/sup] bytes.
>
> The first example represents more of a curiosity than a real problem, for the difference between the advertised “1.44 MB” and the more accurate 1.47 MB is of little practical importance. The second example, however, calls attention to an area where there has been real misunderstanding between buyers and sellers of
> hard drives. The difference between a gigabyte and a gibibyte is approximately 7.5%.
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### Author:  [@Ximenean](https://boards.straightdope.com/u/Ximenean)
#### Post date: [April 20, 2007, 3:41pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/7 "2007-04-20T15:41:52Z")
[QUOTE=awldune]
The SI standard prefix for multiples of 1024 is kibi, mebi, gibi, etc. No one seems to want to use them, and I don’t blame them.
[/QUOTE]
Something’s gonna have to give when we get up into tera- and peta-, with their 10% and 13% discrepancies.
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### Author:  [@naita](https://boards.straightdope.com/u/naita)
#### Post date: [April 20, 2007, 4:57pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/8 "2007-04-20T16:57:24Z")
[QUOTE=CookingWithGas]
It’s very short, just a few lines more than two pages. It does distinguish between the gibi- prefix as gigabinary or 2[sup]1000[/sup] versus the giga- which is 10[sup]9[/sup]. The following text is how the standard closes:
[/QUOTE]
It’s mentioned several times in the thread, but just so this typo doesn’t confuse anyone:
gibi- is 2[sup]30[/sup] = 1 073 741 824
2[sup]1000[/sup] = 1.07150861 × 10[sup]301[/sup]
I can cathegorically say we’ll never have that much storage available, and I need not fear being proven wrong.
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### Author:  [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)
#### Post date: [April 20, 2007, 5:44pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/9 "2007-04-20T17:44:50Z")
[QUOTE=naita]
It’s mentioned several times in the thread, but just so this typo doesn’t confuse anyone:
gibi- is 2[sup]30[/sup] = 1 073 741 824
2[sup]1000[/sup] = 1.07150861 × 10[sup]301[/sup]
I can cathegorically say we’ll never have that much storage available, and I need not fear being proven wrong.
[/QUOTE]
Thanks for the correction. The document said (2[sup]10[/sup])[sup]3[/sup], which I misread as 2[sup]10[sup]3[/sup][/sup].
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### Author:  [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)
#### Post date: [April 20, 2007, 6:10pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/10 "2007-04-20T18:10:02Z")
[QUOTE=Usram]
Something’s gonna have to give when we get up into tera- and peta-, with their 10% and 13% discrepancies.
[/QUOTE]
Why? They aren’t really wrong and a changeover would cost big bucks and aggrevation to explain what they are doing and why. It just is the way they measure things and it is extremely unlikely that a drive manufacturer will decide to change things on its own. There is no reason they have to express everything in the same measure as others.
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### Author:  [@Happy\_Fun\_Ball](https://boards.straightdope.com/u/Happy_Fun_Ball)
#### Post date: [April 20, 2007, 6:22pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/11 "2007-04-20T18:22:52Z")
[QUOTE=Usram]
Something’s gonna have to give when we get up into tera- and peta-, with their 10% and 13% discrepancies.
[/QUOTE]
Nope. I work on a next generation storage technology and, from what I hear, these discrepancies will be used to our advantage in marketing. I have been led to understand that this is pretty much the thinking of the entire industry.
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### Author:  [@Voyager](https://boards.straightdope.com/u/Voyager)
#### Post date: [April 20, 2007, 6:33pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/12 "2007-04-20T18:33:21Z")
Though I don’t know exactly when the nomenclature diverged, there is a good reason for it. Memory is inherently binary, in the sense that memory address is done through an n bit address register, which can address 2\*\*n locations. A kilobit of memory is 1024 bits, and it makes no sense for it to be 1,000. Kilo was used for convenience.
Rotating memories like disk or CD are addressed in a totally different way, using tracks and sectors. (At least they were when I learned this during the dark ages.) I’d suspect each disk actually has a slightly different amount of storage, based on how many bad blocks get mapped out, but the stated capacity is guaranteed.
A Megabyte memory actually contains more than a megabyte of memory cells, by the way. To improve yields, there are usually redundant rows and columns, which get swapped in if manufacturing test (I should say when) finds bad cells. Typically a fuse is burned to show this. However, because of the addressing architecture, you never get access to more cells, even if more are available. It is possible to test and repair in the field, when the product is powered on, but this requires an extensive memory test to be run at power up, and is usually not done. (The test that does get run is I suspect rather feeble.)
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### Author:  [@Ximenean](https://boards.straightdope.com/u/Ximenean)
#### Post date: [April 20, 2007, 6:35pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/13 "2007-04-20T18:35:41Z")
@ **Etyer8** and **Shagnasty**
But surely some canny memory seller will try to steal a march on its competitors by marketing its 128 Petabyte memory sticks, quite correctly, as “144 Petabytes”? It’s not really worth doing that at the moment.
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### Author:  [@Voyager](https://boards.straightdope.com/u/Voyager)
#### Post date: [April 20, 2007, 6:42pm UTC](https://boards.straightdope.com/t/gigabytes-gigabits-gibibytes-etc/400934/14 "2007-04-20T18:42:07Z")
[QUOTE=Usram]
@ **Etyer8** and **Shagnasty**
But surely some canny memory seller will try to steal a march on its competitors by marketing its 128 Petabyte memory sticks, quite correctly, as “144 Petabytes”? It’s not really worth doing that at the moment.
[/QUOTE]
What is the deal with memory sticks? Since they are implemented with flash, they should use the RAM, not the disk, convention, but if they are considered as part of the external storage market I can see them saving a few bucks by not providing the full load.