# What is 256-bit?

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256-bit (2256) is a measure of computer information and an attribute of computer systems. It makes awfully large numbers so it is a common length for cryptography keys that we don't want people to be able to guess or calculate.

How big is 256-bits?

256-bits is too big for us to even imagine!

We're fooled by the integers we can see and understand: "2" and "256" seem so reasonable but every 210 is equivalent to 103 or 10001. That means 2256 is about 10168 (1 with 168 zeroes following) or 100026. So let's have a look at the world in the universe that we can see around us:

• All the data in the world was estimated at 4.4 Zettabytes (273 bits) in 2013. That is more than a 64-bit number could address. If each of those bit were duplicated 273 times we would finally have a number larger than 128-bits. We'd get to 146 bits, yet we'd still be a long way from the range addressable with 256-bits.
• What about stars in the universe? One estimate is an unimaginable 7 x 1022 stars. A Zettabyte is 1021 so this estimate is only one magnitude of difference from all the data in the world. Yet the gulf between this and 256-bits remains immense.
• If we consider the number of atoms in the universe then we creep a little close at 1082. If 96% of the universe is dark matter then that would help a lot … not. We would only get up to about 1085.

 Common uses of 256-bits Category Description CPU No general purpose CPUs are 256-bit but there are general purpose CPUs which have special extensions that use 256-bit instructions. Often the instructions consist of several narrower instructions to be performed in parallel. CPU support It is common for video graphics cards to have 256-bit memory bus widths. Here's an example. Technically, that is the aggregate of what are usually 32-bit interfaces to each memory module as in the diagrams in this article. Operating software na Communications and networking na Displays na Imaging na Audio na Cryptography Cryptography is the main use of bit-lengths 128-bit, 256-bit, and higher. 128-bit is generally the minimum recommended for a private key using a secure algorithm like AES or Triple-DES. Therefore 256-bit would be recommended to ensure longer-term security. Remember that if you are using public keys then the key length will need to be much longer.