Artemy Lebedev
§ 84. How many bytes does a kilobyte contain?February 26, 2002 |
My name is Alice, but
Its a stupid name enough! Humpty Dumpty interrupted impatiently. What does it mean?
Must a name mean something? Alice asked doubtfully.
Of course it must, Humpty Dumpty said with a short laugh: my name means the shape I amand a good handsome shape it is, too. With a name like yours, you might be any shape, almost.
L. Carroll. Through the Looking-Glass
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Todays section deals with a topic covered at the opening pages of any computer manual. The latter customarily starts out with explaining minimal terminology: theres a bit, and when eight bits are brought together, they become a byte. When the number of bytes mounts to 1024, they become a kilobyte. Everyone who cares reads this tiresome blather at least once, stashes it away in ones memory or discards it right away, goes on to thumb through the text, closes the bookand thats it. |
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But its where our inquiry takes its rootsan inquiry whose ending is apt to see manuals authors wind up visiting refresher courses. |
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In the days of old when knights were bold there were computers. And everything about them would be measured in bytes. But computers grew fast, and so did the bytesquickly they grew and finally there were zounds of them. Then the wise computer trailblazers devised the term K that would stand for |
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As for humankind, its development stopped at the decimal number system that was experimentally picked out after prolonged selection a trifle earlier than a computer was invented. In the late 18th century the standard-loving French came up with the metric system of measurements that was based exactly on ten. |
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Housekeeping tip |
In the metric system some Greek or Latin root is usually attached to everything. All these prefixes raise 10 to some power. Say millimeter is All metric indices should be written correctly not to distort their meaning: μ stands for micro , mmilli , Mmega . |
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So we know that the decimal prefix k stems from the word kilo (a thousand), its written in lower case and means multiplication by a thousand. The binary K has nothing to do with kilo just because a computer doesnt count bytes in tensit was people who stepped in to do that. Looking at the words 60 K bytes, some sysadmin said sixty kilo bytes :-). He was overheard by another sysadmin or some handy-andy who thought it worth remembering. So on it went. (Example of a similar interpretation of a letter in a metric way: megabytemeter). |
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This is the way we got an interpretation of the unit K byte (kabyte) as a kilobyte, although nobody originally meant that. The other meanings were selected in a similar way: megabyte, gigabyte, terabyte All these words sounding like metric units are in fact different powers of two. Thinking in the powers of two is way too hard: nobody thinks of a megabyte as 1024 kilobytes. |
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But thats only half of the story. The most interesting thing is that apart from binary kilobytes, there are decimal ones. And we have to deal with them every day. |
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It is a historical tradition that computer memory (RAM) is measured in K-bytes. Therefore 10 MB of memory are 10,485,760by no means 10,000,000bytes. |
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The larger portion of hard drives makers indicates the volume of their produce in decimal megabytes and gigabytes. In contrast to that, operating systems see hard drives from the viewpoint of binary megabytes and gigabytes. So when you buy a 50 GB hard drive, be prepared for it to fall 3.5 GB short of the target. The remaining 46.5 GBin binary gigabytes!is the fair volume of the drive. |
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The telecom industry has its own life to live. It has a long-standing custom to measure everything in decimal kilobytes. The data transfer speed is normally measured in kilobits per second (kb/s). With favorable weather conditions, a 28.8 kb/s modem would transfer exactly 28,800 bits per second, or about three binary kilobytes and a half per second on average. If you happen to come across a 28.8 K modem, remember that the K index standing for kb/s is a fancy thing coined by marketing specialists thats never used by professionals. |
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A special case was with the invention of the 3.5-inch diskette. Every box has the 1.44 MB marking on it. Everybody remembers this number. And everybody remembers that the floppy can hold less than it is promised. Why is that? Because the disc volume is indicated in decimal bytes: 1,440,000 decimal bytes are equal to 1.44 decimal MB. But in binary bytes its 1.4 MB. |
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If by now youve gotten a little tired of the difference between binary and decimal units, imagine how much dough hardware producers earn on that. Advertising will stick at nothing to make the figure look as enticing as ever. This entertaining come-on will mean nothing, but greenbacks in your purse will feel a little easier at heart when you eventually shell out. Thats all you are actually expected to do. |
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Obiter dictum |
If you happen to look at LCD monitors specifications, take notice of the following remark: screen diagonal15″ (an equivalent of 17″ CRT). What it means is just that the manufacturers of conventional picture tubes measure their diagonals before the casing is added on. There are no consumers in the whole world whod go shopping with an inch ruler to measure the screen size. The main thing is winning the competition of beautiful figures. Since the hi-tech industry has not so far learnt how to make flat panel displays with an invisible area, advertising departments are forced to let out the secrets of last years advertising tricks. |
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Seeking to somehow sort out this schizophrenic situation, the International Electrotechnical Commission (IEC) tried to get things in order in March 1999. The standards body proposed new names for binary measurements, coining new prefixes and suggesting that kilobyte be renamed into kibibyte (KiB), megabyteinto mebibyte (MiB) etc. In November 2000 these changes were officially written into international standards. |
See: IEC 600272 (200011) Letter symbols to be used in electrical technology Part 2: Telecommunications and electronics |
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The originally good idea floppedon the day this section was composed a search for kibibyte in Yandex, Russias number one search engine, turned up seven sites. Of these seven, two were collections of anecdotes. |
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A good name is an essential thing, after all, if you aspire to worldwide recognition: beeping was out of anybodys plans, while mebibyte sounds equally weird in all languages. |
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Finally, below you will find a table with correct English names and acronyms. |
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*
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This acronym may exist, but its too long and open to various readings. |
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