< > [Programming](../index.html) > MPU
##MPU
Microprocessor is a CPU on a single chip.<br>
CPU (Central Processing Unit) is an integrated circuit within a computer that carries out instructions.<br>
<p align="center">
<img src="cpu0.gif" width="50%" height="50%">
<br>
Relationship between the elements of the CPU, input and output, and storage.
</p>
<p align="center">
<img src="cpu1.gif" width="50%" height="50%">
<br>
Block diagram of a basic uniprocessor-CPU computer. Black lines indicate data flow, whereas red lines indicate control flow; arrows indicate flow directions.
</p>
<p align="center">
<img src="chip_labeled.png" width="50%" height="50%">
<br>
[Overview of the ARM1 chip](http://www.righto.com/2015/12/reverse-engineering-arm1-ancestor-of.html)
</p>
##Types of MPUs
####Depending on word size:
<ul>
<li>8bit</li>
<li>16bit</li>
<li>32bit</li>
<li>...</li>
</ul>
####Depending on purpose:
<ul>
<li>general</li>
<li>floating point calculations</li>
<li>image processing</li>
<li>...</li>
</ul>
####Depending on ISA (Instruction Set Architecture):
#####RISC(Reduced Instruction Set Computing) => Apple iPod, AVR Arduino, ARM, Nintendo
<ul>
<li>emphasis on Software</li>
<li>large number of simply encoded and short instructions in a pipeline</li>
<li>all instructions are similar in length and execution time</li>
<li>uses low cycles per second and single-clock</li>
<li>uses RAM to store assembly level instructions </li>
<li>used in portable devices because it is power efficient and suited for simple programs</li>
</ul>
#####CISC(Complex Instruction Set Computing) => Intel and x86 (32-bit and 64-bit) family
<ul>
<li>emphasis on Hardware</li>
<li>small number of variable complexity instructions</li>
<li>all instructions can be different in length and execution time</li>
<li>uses high cycles per second and multi-clock</li>
<li>used in intensive workstations and cloud computing because it better handles complex programs</li>
</ul>
<br>
The execution time<br>
<p align="center">
<img src="execution_time.png">
<br>
</p>
of a program depends on<br>
N: total number of instructions in the program.<br>
CPI: average number of cycles in each instruction.<br>
CT: clock cycle time.<br>
<p align="center">
<img src="risc_cisc_table.png">
<br>
</p>
The CISC instructions are closer to the high-level languages, while the RISC instructions are closer to the signel-step micro-instructions.<br>
<p align="center">
<img src="risc_cisc.gif">
<br>
</p>
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