Instruction Decoder

The instruction decoder of a processor is a combinatorial circuit sometimes in the form of a
read-only memory, sometimes in the form of an ordinary combinatorial circuit. Its
purpose is to translate an instruction code into the address in the micro memory where
the micro code for the instruction starts. 

A decoder is a device which is the reverse, undoing the encoding so that the original
information can be retrieved. The same method used to encode is usually just reversed in
order to decode.This unit receives the programming instructions and decodes them into
a form that is understandable by the processing units, i.e. The ALU or FPU Then, it
passes on the decoded instruction to the ALU or FPUs as desired.

Bus Interface Unit

The bus interface unit is the part of the processor that interfaces with the rest of the PC.
Its name comes from the fact that it deals with moving information over the processor
data bus, the primary conduit for the transfer of information to and from the CPU. The
bus interface unit is responsible for responding to all signals that go to the processor,
and generating all signals that go from the processor to other parts of the system.
It receives instructions & data from main memory to be processed and operations. After
the operations are processed it then sends back the information (processed data) to the
cache. It also receives the processed data to send it to the main memory.

On-Chip Cache Memory (2)

L2, cache memory, which is on a separate chip from the microprocessor but faster to
access than regular RAM.
It is the small size and proximity to the microprocessor makes access times short,
resulting in a boost in performance. Microprocessors predict what data will be required
for future calculations and it pre-fetches that data and places it in the cache so that it is
available immediately when the need arises.

On-Chip Cache Memory (1)

That small amount of memory located on the same chip as the microprocessor is called
On-Chip Cache Memory.
The microprocessor stores a copy of frequently used data and instructions in its cache
memory. When the microprocessor desires to look at a piece of data, it checks in the
cache first.  If it is not there, only then the microprocessor asks for the same from the
main memory.

Cache

A cache is a collection of duplicate data, where the original data is expensive to fetch or
compute (usually in terms of access time) relative to the cache. Future accesses to the
data can be made by accessing the cached copy rather than refetching or recomputing
the original data, so that the perceived average access time is lower. Caches may mark the
cached data as 'stale' when the original data is changed, but this is not always the case.

Solution to the Bottleneck Problem

In order to eliminate the solution it was suggested to make the main memory faster. But
that evolved a problem that the 1-ns memory is extremely expensive as compared the
currently popular 100-ns memory.
Finally it was decided that in addition to the relatively slow main memory, put a small
amount of ultra-fast RAM right next to the microprocessor on the same chip and make
sure that frequently used data and instructions resides in that ultra-fast memory
It increases the performance. It supports better over performance due to fast access to
frequently  used data and instructions.

The Main Memory Bottleneck

Modern super-fast microprocessors can process a huge amount of data in a short
duration. They need data to be processed at the same speed. Other wise they have to sit
idle and wait for the input/data, because speed of input is rather small then processing
of data. They require quick access to data to maximize their performance. If they don’t
receive the data that they require, they literally stop and wait, this results in reduced
performance and wasted power.
Current microprocessors can process an instruction in about ns (nanosecond).  Time
required for fetching data from main memory (RAM) is of the order of 100 ns

Micro-controllers

A microcontroller is a microprocessor optimised to be used to control electronic
equipment. Microcontrollers represent the vast majority of all computer chips sold, over
50% are "simple" controllers, and another 20% are more specialized decipline
processors. While you may have one or two  general-purpose microprocessors in your
house (you're using one to read this), you likely have somewhere between one and two
dozen microcontrollers. They can be found in almost any electrical device, washing
machines, microwave ovens, telephones etc.
A microcontroller includes CPU, memory for the program (ROM), memory for data
(RAM), I/O lines to communicate with peripherals and complementary resources, all
this in a closed chip. A microcontroller differs from a standalone CPU, because the first
one generally is quite easy to make into a working computer, with a minimum of external
support chips. The idea is that the microcontroller will be placed in the device to control,
hooked up to power and any information it needs, and that's that.

Microprocessor system

Microprocessors are powerful pieces of hardware, but not much useful on their own.  
They do not have the sense of their own.  Like the human sample it needs some
instructions inputs and outputs to process some task. As per instruction given to the
microprocessor.
A microprocessor system is microprocessor plus all the components it requires to do a
certain task.
Shortly, a microprocessor needs help of some components to make up the task to fulfill.
These components are input, output, storage, and memory. All these components and
microprocessor make up a microprocessor system.
Personal Computer is an example of microprocessor System. Another example is the
microcontroller.

And are made of the following materials

Silicon - semiconductor
Copper - conductor
Silicon Dioxide - insulator