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A kilobyte is actually 1000 bytes. "kilo-" is an SI prefix meaning "1000".

  • 1 km = 1000 meters
  • 1 kg = 1000 grams
  • 1 kB = 1000 bytes

When dealing with computer memory, the addresses for each memory location are typically binary numbers, which means the total number of addresses is a power of 2. It makes the most sense to use all of these positions, so the total capacity of a memory will typically be a power of two.

Since 210 is equal to 1,024, it is often approximated as "1 kilobyte" in speech, but this is just a shorthand, not a real definition.

RAM manufacturers treat this as a literal meaning instead of an approximation, though, and extend this to higher powers, which conflicts with the way units are used elsewhere. So a "1 GB" RAM IC has 230 = 1,073,741,824 bytes instead of 1,000,000,000 bytes, a 7% error. On the other hand, a 1 GB Flash memory actually doeshave around 1,000,000,000 bytes, as you would expect.

"kB" or "KB" can mean either 1024 bytes or 1000 bytes, depending on who you ask. Both meanings have been in use since the early days of computing, confusing users ever since.

kilo- means 1000, and has for centuries, so where did 1024 come from? The answer is binary addressing.

Your basic transistor, the foundation for all things computer, has 2 states (on/off), which is known as binary. So modern computers of all types use the binary numbering system (0/1 = off/on).

Memory addresses in computers are a number of bits wide. For instance, the old 6502 microprocessor had memory addresses 16 bits 'wide'.

With 10 bits, for instance, a computer can address 210 memory locations, which is 1024. With 16 bits, a computer can address 216 memory locations. So the number of memory locations is always a power of two. It wouldn't make much sense to make memory chips that don't use all of the addressable locations, so all memory is in powers of two. (This doesn't apply to other computer components, however. Hard drives, disk drives, DVDs, and other media, clock speeds and data rates and networking speeds are all measured in powers of 10.)

But 1024 is 210 (2 to the 10th power), conveniently close to 103 (1000). In computers, base-2 shows up over and over again. It's easier to approximate and say "1k" instead of 1024. 1 kilo is normally 1000, as per the metric system's prefixes.

In this case, the next higher size of memory chips was often 2x or 4x the previous size. This pulled folks away from the normal base-10 thinking toward base-2 thinking ... and we ended up with something that sounds like it is based on powers of 10, but is really based on powers of 2.

Officially, 1000 is the only valid meaning, and "k" was used by engineers for 1024 just as an approximation. (2048 bytes isequal to 2.0 kB, after all.) Over time, this approximation became used by marketing types as if it was actually defined as1024, rather than just being used as an approximation.

In 1968, for instance, Donald Morrison talked about how it was confusing to tell laymen that doubling a 32K memory produced a 65K memory. He proposed to end the confusion by using the Greek letter κ (kappa) to mean 1024, but this never stuck. Instead, people started using capital K to mean 1024, which further increased confusion instead of helping.

Nowadays however, there is a new prefix to be used for the non-standard meaning:

  • 1 kibibyte (KiB) is 1024 bytes
  • 1 kilobyte (kB) is 1000 bytes

So too for the old megabyte which was 220 bytes:

  • 1 mebibyte (MiB) is 1,048,576 bytes
  • 1 megabyte (MB) is 1,000,000 bytes.

Higher units like terabyte have always been used with the 1000x meaning except in rare cases.

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11y ago
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15y ago

In computer we store memory with binary 0 or 1. And memory is generally known as addressing capability of memory chip.So if we have a chip with 2 address line we can address(means select) 4 byte(i.e. 2 ^ 2) or 4 memory locations in 8-bit(1 byte) chip or processor.

Hence here memory capacity becomes 4 Bytes.

Similarly if 3 address lines are there then we can address 8 bytes(2^3).

4 address lines are there then we can address 16 bytes(2^4).

9 address lines are there then we can address 512 bytes(2^9).

10 address lines are there then we can address 1024 bytes(2^10).

11 address lines are there then we can address 2048 bytes(2^11).

and so on.

We can mark here the memory capacity does not reach any where 1000(conventionally kilo) byte but nearest approximation is 1024 bytes(in computer language Kilo i.e. 1024=1 KB) which is 24 nos more but we can not neglect in case of computation or real field so 1 KB is 1024 Byte rather than 1000 Bytes.

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12y ago

1024 is the closest number to 1000 you can reach in the binary system of counting. Hard drive manufacturers use decimal counting to rate there drives which is why you don't get exactly 100GB out of a 100GB hard drive.

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6y ago

This is due to the binary nature of bytes:

For 1 digit in binary, you can represent 2 numbers: 0 and 1

For 2 digits in binary, you can represent 4 numbers: 00, 01, 10, 11

For 3 digits in binary, you can represent 8 numbers: 000,001, 010, 011, 100, 101, 110, 111

This carries on : For n digits in binary you can represent 2n numbers

This is because each digit has two states (1 and 0), so for n=3:

First digit has two states, Second digit has two states, Third digit has 2 states = 2 x 2 x 2 = 23

In the special case above, we have a ten digit binary number, which gives you 210 numbers = 1024.

Technically though 1 kilobyte (kB) = 1000bytes

1024 bytes is known as 1 Kibibyte

The decimal prefixes go up in power multiples of 3, so

100 = 1 => no prefix

103 = 1,000 => 1 Kilo (k)

106 = 1,000,000 => 1 Mega (M)

109 = 1,000,000,000 => 1 Giga (G)

1012 = 1,000,000,000,000 => 1 Tera (T)

1015 = 1,000,000,000,000,000 => 1 Peta (P)

The binary prefixes go up in power multiples of 10, so

20 = 1 => byte

210 = 1,024 => 1 Kibibyte (kiB)

220 = 1,048,576 => 1 Mebiabyte (MiB)

230 = 1,073,741,824 => 1 Gibibyte (GiB)

240 = 1,099,511,627,776 => 1 Tebibyte (TiB)

250 = 1.12x1015 => 1 Pebibyte (PiB)

Beware! Hard drives manufactures tend not to use this system when quoting disk sizes... They use 1 MB = 1,000,000 bytes, 1 GB = 1,000,000,000 bytes, etc

So when you buy a 1TB Hard drive, it won't have 1TiB capacity!

1TB = approx 935.5GiB

Windows and other OSs use the binary system, as you can see the hard drive manufacturers can use this difference to advertise larger capacities than may be apparent.

At low numbers (ie kilos and megas) the difference was not really appreciable, but since the difference is getting greater as computers use more memory and disk get bigger, etc, the two standard have been introduced. Unfortunately most people carry on using the decimal prefixes, when they mean the binary ones.

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13y ago

Computers operate in binary, meaning 1's and 0's, or in other words, "on" and "off", literally. This is how all digital machines operate. 1 and 0 are two numbers, so that means that computers run off of base-two numbering systems (2x), rather than base-ten like people do (10x). 210 (Two to the tenth power) is 1,024, not 1,000 (which is 103). Every tenth power in base-two (210, 220, 230, 240, 250, etc.) is a new designation prefix, such as Kilo, Mega, Giga, Tera, Yotta, respectively. So 210 bytes is one kilobyte, or 1,024 bytes. 1,024 kilobytes (220 bytes) is one gigabyte, and so on.

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12y ago

the parameters in computers are summarised in the number of "2"



and 1024 is called 1kb.

(attention: kilo is: 10x10x10. but in computers kilo is 1024)

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14y ago

It is used because it is 2 to the 10th power, 2 being the binary function. It was realized that it would be easier to use 2^10 than 10^3, because they are so close in size.

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11y ago

No. 1024 bytes is a kibibyte (KiB).

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Q: Why is one KB not exactly 1000 bytes?
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Short Name = Full name = Size in bytes = Size in bits KB = Kilobyte = 1000 Bytes = 8000 Bits Kb = Kilobit = 125 Bytes = 1000 Bits in previous answer there is mistake kb=12.5 bytes

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