System Architecture.

Friday 2/11/18


Von Neumann Architecture-The von Neumann architecture also known as the von Neumann model or Princeton architecture is a computer architecture.


MAR(Memory address register)- In a computer, the Memory Address Register is the CPU register that either stores the memory address from which data will be fetched from the CPU, or the address to which data will be sent and stored.


MDR(Memory data register)-The Memory Data Register or Memory Buffer Register is the register of a computer's control unit that contains the data to be stored in the computer storage , or the data after a fetch from the computer storage.


Program Counter-A program counter is a register in a computer processor that contains the address (location) of the instruction being executed at the current time.


Accumulator-In a computer's central processing unit (CPU), an accumulator is a register in which intermediate arithmetic and logic results are stored.


ALU(Arithmetic logic unit)-An arithmetic logic unit is a combinational digital electronic circuit that performs arithmetic and bitwise operations on integer binary numbers.


CU(Control unit)-A control unit (CU) handles all processor control signals
.
Cache-Cache memory is extremely fast memory that is built into a computer’s central processing unit (CPU), or located next to it on a separate chip.


Fetch/Execute-An instruction cycle is the basic operational process of a computer. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction dictates, and carries out those actions.


Busses-A wire that carries information from one place to another.

Hardware.

Embedded System:
An embedded system is a dedicated computer system designed for one or two specific functions. This system is embedded as a part of a complete device system that includes hardware, such as electrical and mechanical components. The embedded hardware is unlike a general purpose computer as it made to be specialised but a general purpose computer is made for lots of different purposes.
Some different thing you may find at your home are;

• Dishwasher
• Fridge
• Freezer
• Washing Machine
• Microwave
• Kettle
• Smartlights
• Smoke Alarm
• Burglar alarm.

Binary And Hexadecimal.

Binary


Binary consists of the values 0 and 1, False and true. This is because computers can only understand this. Binary looks like this:


128  64  32  16  8  4  2  U
0       1     0    0   0  1  1  0


This is equal to = 70.


Hexadecimal:
Hexadecimal consists of numbers and letters, 1 2 3 4 5 6 7 8 9 A B C D E F, this is equal; to 1 2 3 4 5 6 7 8 9 A=10 A=11 A=12 A=13 A=14 A=15.
For example: the value A3 is equal to 10100011.


Somme more examples are;


01101110 = 124
11111111 = 255
00001111 = 15
7 = 00000111
4 = 00000100
74 = 01001010


Some extra information can be found on the bbc bitesize website; BBC BITESIZE

Boolean Logic

Logic Gates:


There are different types of logic gates depending upon what the logic gate is needed to do.


OR Gates


An OR gate will give a true(1) if either of the values give input as a true. A logic table for this is:


ABQ
0 0 0
0 1 1
1 0 1
1 1 1


AND Gates 
 An AND gate will give a true statement if both of the inputs are true. A logic table for this is:


ABQ
0 0 0
0 1 0
1 0 0
1 1 1


NOT Gates


A NOT gate will give a true statement if a false statement is the input. A logic table for this looks like;
AQ
0 1
1 0


A very good website for extra revision is BBC Bitesize as this has a few different examples of logic gates: BBC Bitesize


Think about what happens when you get into a lift - the doors close, you press the button to say which floor you want, and the lift starts moving.
What happens if the doors close but you don’t press a button to choose a floor? Nothing happens. The lift doesn’t know which floor you want, so it stays where it is.
Alternatively, what happens if you are too quick to press the floor button, and press it before the doors have closed? Well, of course the lift doesn’t start moving, that would be extremely dangerous. It will wait until the doors close.
The lift will only move if the door is closed AND you have pressed a floor button. The door has a sensor which produces an electrical signal when the door is closed. The floor button produces an electrical signal when you choose a floor. The control circuit inside the lift monitors both input signals, and only when they are BOTH on, it produces an output signal to drive the lift motor.
An AND gate has two input signals and one output signal.
The two input signals can each be either on or off. When we describe logic gates we normally refer to these states as 0 or 1.

The state of the inputs controls the state of the output. The output value is 1 (on) if both inputs are 1, otherwise it is 0 (off). It is called an AND gate because the output will only be 1 if inputs A AND B are both one.

An OR gate has two inputs and one output. It is similar to an AND gate, except that the output obeys different rules.
The two inputs can each have values 0 or 1.
The state of the inputs controls the state of the output. The output value is 1 if either (or both) inputs are 1, otherwise it is 0. It is called an OR gate because the output will be 1 if input A OR input B is one.
An NOT gate is a little different, as it only has one input and one output.
The input can have a value of 0 or 1.
The state of the input controls the state of the output. The output value is 1 if the input is 0, and it is 0 if the input is 1. In other words, the output value is the opposite of the input value.
We call it a NOT gate, because if the input is true, the output is NOT true, and vice versa. NOT gates are sometimes called inverting gates (because they invert the logical sense of the input), and we sometimes use the term negative logic when we are talking about NOT gates. All these different terms mean the same thing.
Here is the symbol for an NOT gate. The input is labelled A, the output is labelled Q.





We can combine two or more gates to perform more complex functions.
In this diagram, we have three inputs (A, B and C) and one output (Q). We are using an AND gate and an OR gate.

We have also labelled the output of the AND gate as D. D is not an input, it is an intermediate value which we will use when calculating the truth table.

Introduction

This is where I am keeping my computer science work that I will look back on when revising.