# Kiến thức cơ bản

**Bits, Bytes, Mega, Giga, Tera (explained) **

1 bit = a 1 or 0 (b)

4 bits = 1 nybble (?)

8 bits = 1 byte (B)

1024 bytes = 1 Kilobyte (KB)

1024 Kilobytes = 1 Megabyte (MB)

1024 Megabytes = 1 Gigabyte (GB)

1024 Gigabytes = 1 Terabyte (TB)

1024 Terabytes = 1 Petabyte (PB)

Common prefixes:

- kilo, meaning 1,000. (one thousand) 10^3 (Kilometer, 1,000 meters)

- mega, meaning 1,000,000. (one million) 10^6 (Megawatt, 1,000,000 watts)

- giga, meaning 1,000,000,000 (one billion) 10^9 (Gigawatt, 1,000,000,000 watts)

- tera, meaning 1,000,000,000,000 (one trillion) 10^12

- peta, meaning 1,000,000,000,000,000 (one quadrillion) 10^15

The smallest amount of transfer is one bit. It holds the value of a 1, or a 0. (Binary coding). Eight of these 1's and zero's are called a byte.

Why eight? The earliest computers could only send 8 bits at a time, it was only natural to start writing code in sets of 8 bits. This came to be called a byte.

A bit is represented with a lowercase "b," whereas a byte is represented with an uppercase "b" (B). So Kb is kilobits, and KB is kilobytes. A kilobyte is eight times larger than a kilobit.

A simple 1 or 0, times eight of these 1's and 0's put together is a byte. The string of code: 10010101 is exactly one byte. So a small gif image, about 4 KB has about 4000 lines of 8 1's and 0's. Since there are 8 per line, that's over (4000 x 8) 32,000 1's and 0's just for a single gif image.

How many bytes are in a kilobyte (KB)? One may think it's 1000 bytes, but its really 1024. Why is this so? It turns out that our early computer engineers, who dealt with the tiniest amounts of storage, noticed that 2^10 (1024) was very close to 10^3 (1000); so based on the prefix kilo, for 1000, they created the KB. (You may have heard of kilometers (Km) which is 1000 meters). So in actuality, one KB is really 1024 bytes, not 1000. It's a small difference, but it adds up over a while.

The MB, or megabyte, mega meaning one million. Seems logical that one mega (million) byte would be 1,000,000 (one million) bytes. It's not however. One megabyte is 1024 x 1024 bytes. 1024 kilobytes is called one Megabyte. So one kilobyte is actually 1024 bytes, and 1024 of those is (1024 x 1024) 1048576 bytes. In short, one Megabyte is really 1,048,576 bytes.

There is a difference of about 48 KB, which is a decent amount. If you have a calculator, you will notice that there is actually a 47KB difference. There is a difference of 48,576 bytes, divided by 1024, and you get the amount of real kilobytes... 47.4375

All of this really comes into play when you deal with Gigabytes, or roughly one billion bytes. One real Gigabyte is actually 1024 bytes x 1024 bytes x 1024 bytes...1,073,741,824. However, most people like to simplify this by simply saying that one Gigabyte is only 1,000,000,000 (one billion) bytes; which makes sense because the prefix Giga means one billion.

**References**

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