COMPUTER ARCHITECTURE

Memory Data Register (MDR) Process

Fetch

•   The contents of the Program Counter (PC) are transferred to the Memory Address Register (MAR).
•   Address bus used to transfer this address to the main memory
•   The contents of the addressed memory location are moved into the Memory Buffer Register (MBR), also known as MDR.
•   This transfer uses the data bus.
•   The PC is then incremented.
•   The content of the MBR is transferred to the Current Instruction Register (CIR).

Decode

• The instruction held by the CIR is decoded.
• The Control Unit decodes the instruction, splitting it into an operation code (opcode) and operand.

Execute

• Data is fetched if necessary.
• The opcode identifies the instruction or operation to be executed.
• The relevant part of the processor executes the instruction.
• The result is stored in the accumulator.

Definitions:

• Opcode: Operation Code.
• Operand: The location of the register/data (memory location).

Central Processing Unit (CPU):

• The CPU is essential for processing all data and instructions.
• It’s the most important component of a computer, processing instructions, and data inputted into the computer to produce output.

RAM and Software:

• RAM holds instructions, the operating system, currently open programs/applications, and data.
• System software provides essential functionalities needed to run other software.
• Application software serves specific user purposes.
• Graphical User Interface (GUI) is a user-friendly interface.
• There are two types of addressing: direct and indexed.

Control Unit and ALU

• The Control Unit coordinates all computer operations, sending out control signals like the clock signal.
• Speeding up the clock signal (measured in hertz, currently gigahertz) increases operation speed.
• The Arithmetic Logic Unit (ALU) performs all arithmetic calculations and logical comparisons.
• Logical operations typically involve comparing data items.

A>B        X=Y

CPU Operations

1. Fetch: Fetches the next instruction and any related data from the main memory.
2. Decode Decodes the instruction.
3. Execute: Carries out the instruction.

• The Control Unit is responsible for decoding and executing instructions.
• The CPU includes a Program Counter (register) to fetch the next instruction from memory.

Registers and Buses

• General-purpose registers: Hold data like numbers during arithmetic calculations.
• MAR: Holds the address.
• MDR: Holds the data.
• A bus is a set of parallel wires connecting two or more components of the computer.
• The address bus (unidirectional) carries addresses from the CPU to the memory.
• The control bus (bidirectional) sends control signals.
• The data bus (bidirectional) transfers data.

The information about buses:

• The CPU sends addresses to memory on the address bus.
• Data from the memory is returned to the CPU on the data bus.
• The Control Unit uses the control bus, MAR uses the address bus, and the MDR uses the data bus.

Assembly language is a low-level language that is used for instructions in a machine. In order to translate the assembly code into machine code, you require an assembler. The assembly language is broken up into 2 parts. The first part is the OP Code. Operational Code. OP is basically the instruction that needs to be executed. Operand is the second part. Operand is the location/ address/ data that needs to be processed.

The number of cores, size of the cache and speed of the clock can affect the performance of a CPU 

REGISTERS:

PC= program counter 

CIR= Current Instruction Register 

MDR= Memory Data Register 

AC= Accumulator 

CU=Control Unit 

MAR= Memory Address Register

MEMORY The memory unit consists of RAM, sometimes referred to as primary or main memory.  Unlike a hard drive (secondary memory), this memory is fast and also directly accessible by the CPU.

ALU= Arithmetic Logic Unit 

CACHE

CPU= Central Processing Unit  

RAM= Random Access Memory 

A bridge prevents the signal from changing from one input to another 

An embedded system is used to perform a dedicated function, e.g. domestic appliances, cars, security systems, lighting systems, or vending machines. This is different from a general-purpose computer that is used to perform many different functions, e.g. a personal computer (PC) or a laptop