Bit vs byte: one binary digit, and a group of eight
A bit (binary digit) is the smallest unit of information: a single 0 or 1, which in a circuit is one wire that is low or high. A byte is a group of 8 bits, enough for 256 different values (00000000 to 11111111, or 0 to 255), and it is the unit computers use to address memory and measure files. Half a byte, 4 bits, is a nibble, which is exactly one hexadecimal digit, so a byte is always written as two hex digits. The symbols differ only in case: a lowercase b means bits and an uppercase B means bytes, so 100 Mb/s is a hundred million bits per second, while 100 MB is a hundred million bytes. To convert, divide bits by 8 to get bytes, or multiply bytes by 8 to get bits.
Where each unit is used
Bits are used for things that move one bit at a time: network and internet speeds (Mbit/s, Gbit/s), serial links and the width of a bus or a register (an 8-bit or 64-bit processor). Bytes are used for things that are stored: file sizes, memory and disk capacity. That is why a 100 Mbit/s connection downloads at most 12.5 megabytes per second (100 / 8), before any protocol overhead. Larger units come in two flavours, decimal (1 kB = 1000 bytes) and binary (1 KiB = 1024 bytes), compared on our KB vs KiB page.
See bits and bytes live in digiwleea
In digiwleea a bit is literally a wire you can see turn 0 or 1, and a byte is eight of them side by side. The course's CPU is an 8-bit machine: you build its 8-bit registers and 8-bit adder from transistors up, one bit at a time. To practise reading bytes, play the binary game or convert values in the binary converter; the binary and hexadecimal lessons explain why two hex digits make one byte.
Common sizes
| Unit | Bits | Values it can hold |
|---|---|---|
| 1 bit | 1 | 2 (0 or 1) |
| 1 nibble | 4 | 16 (one hex digit) |
| 1 byte | 8 | 256 |
| 2 bytes (16-bit word) | 16 | 65,536 |
| 4 bytes (32-bit word) | 32 | 4,294,967,296 |
No sign-up is needed to start: open the lab and place your first transistor, or read the free theory course. The account (and the AI tutor) are optional.
More comparisons: Digital logic concepts compared
See for yourself: build a logic gate from transistors in the simulator, then follow the path from sand to an 8-bit CPU.
Open the digiwleea lab →Frequently asked
What is the difference between a bit and a byte?
A bit is a single binary digit, 0 or 1. A byte is a group of 8 bits, which can represent 256 different values.
How many bits are in a byte?
Eight. Half a byte, 4 bits, is called a nibble and corresponds to one hexadecimal digit.
Is Mbps the same as MB/s?
No. Mbps (or Mb/s) is megabits per second and MB/s is megabytes per second; divide Mbps by 8 to get MB/s, so 100 Mbps is at most 12.5 MB/s.
Why does a byte have 8 bits?
Eight bits give 256 values, enough for a character set such as ASCII plus extras, and 8 is a power of two, which makes addressing and hardware simple. Early computers used other sizes, but the 8-bit byte became the standard.
What does b and B mean?
Lowercase b means bit and uppercase B means byte, so kb is kilobits and kB is kilobytes.