Bus width is the number of bits that a [microprocessor](https://www.ampheo.com/c/microprocessors) can transfer simultaneously over a bus (data bus, address bus, or control bus).
Think of it like the number of lanes on a highway — more lanes allow more cars (bits) to move in parallel.

**1. Types of Bus Width**
**(a) Data Bus Width**
Number of bits the CPU can read/write to memory or I/O in one operation.

Example:

* 8-bit bus → moves 1 byte per transfer.
* 32-bit bus → moves 4 bytes per transfer.

**(b) Address Bus Width**
* Number of bits used to address memory locations.
* Determines maximum directly addressable memory:


**(c) Control Bus Width**
* Carries control signals (read/write, clock, interrupts).
* Width varies depending on architecture.

**2. How Bus Width Affects Performance**
**(a) Data Throughput**
Wider data bus = more data moved per clock cycle.

Example:
At 100 MHz:

* 8-bit bus → 100 MB/s max theoretical transfer.
* 32-bit bus → 400 MB/s max theoretical transfer.

**(b) Memory Access**
If the CPU needs 32-bit data but only has an 8-bit bus, it must perform 4 separate reads → slower execution.

**( c) Instruction Size & Execution**
On some architectures, instruction fetch width is tied to data bus width — wider buses allow fetching larger instructions or multiple instructions faster.

**(d) Addressing Capability**
* A larger address bus allows more RAM/ROM to be connected without bank switching.
* E.g., a 16-bit [microcontroller](https://www.ampheo.com/c/microcontrollers) with an 8-bit data bus can still address 64 KB, but moves only 1 byte at a time.

**3. Real-World Example**
* [Intel](https://www.ampheo.com/manufacturer/intel) [8088](https://www.ampheo.com/search/8088) (used in original IBM PC):

16-bit internal registers, 8-bit external data bus → slower memory access than the 8086 (16-bit data bus).

* ARM Cortex-M4 ([STM32F4](https://www.ampheo.com/search/STM32F4) series):

32-bit internal registers, 32-bit data bus → can fetch entire words in one cycle.

**In short:**

* Data bus width → affects how fast data moves.
* Address bus width → affects how much memory can be accessed.
* For performance, wider buses generally mean higher throughput, but clock speed, cache, and memory latency also play big roles.