What is computer architecture
Computer architecture refers to the overall organization of a computer system. It is analogous to a blue print.
The architecture of a computer specifies
1)The functionality of the major components.
2) The intercommunication among components
Types of computer architecture
1.Von Neumann architecture
2. Harvard architecture
3. Instructions set architecture
4. Microarchitecture
……….. Is the fundamental architecture for every digital computer
Von Neumann architecture
Who proposed von Neumann architecture
John von Neumann
Von Neumann architecture consist of
- CPU also known as processor
- Memory
- Interconnection between the memory and the CLU
How does von Neumann architecture execute instructions
- A von Neumann machine executes a single instructions at a time
- Each instruction operates on only a few pieces of data
Discuss the CPU
- The CPU is brain of the computer
- The CPU, also called the “processor” is the unit that does all the processing in a computer
- This unit of the computer retrieves and executes instructions.
- The CPU is an integrated circuit that performs the calculation that runs a computer.
- The CPU performs
Arithmetical
Logical
Input/output
instructions that passed from an operating system
The CPU is made up three essential components, what are there??
- Arithmetic and logic unit (ALU)
- Control unit ( CU)
- Registers
Discuss ALU ( Arithmetic and Logic Unit)
- The ALU is a digital circuit ( integrated circuit) used to perform arithmetic and logic operation.
- ALU represents the fundamental building block of the CPU in any computer
- Modern CPU contain very powerful and complex ALU’s
Examples of arithmetic operations carried out by ALU are
- Addition
- Subtraction
- Multiplication
- Division
Examples of logic operations in ALU are
- AND
- OR
- NOT
When operations become more and complex the ALU…………
Also becomes more complex and expensive and takes more space in the computer and dissipates more heat
Discuss the CU ( control unit)
The CU tells the ALU what operations to perform on data and ALU stores the results in an output register
The CU moves the data to the output devices
Discuss registers
Registers are special transistors that store data and instructions as they are being manipulated by the control unit and ALU.
Registers are essentially extremely fast memory locations within the CPU that are used to create and store the results of the CPU operations.
Every data to be processed by CPU must be in the registers
Essentially, registers are the memory locations to which data are sent and retrieved.
Computer differ from one another in……..
1.The number of registers
2.Register types
3.Length of each register
4. They also differ in the usage of each register
General purpose register are used for multiple purposes and assigned a variety of functions by programmers
So registers are user visible and modifiable. Others are not e.g
USER VISIBLE AND MODIFIABLE
1.General purpose
2.Data(e.g, accumulators)
3Address( e.g base, addressing, index addressing)
CONTROL ( NO VISIBLE TO USERS)
1. Program counter (PC)
2. Instructions Decoding Register (IR)
3. Memory Address Registers (MAR)
4. Memory Buffer registers (MBR)
STATE REGISTERS ( VISIBLE TO USER BUT NOT DIRECTLY MODIFIABLE)
1.Program status word (PSW)
Types of registers
- Memory access registers (MAR)
- Instruction fetching registers
- Conditions registers
- Special address registers
Memory access registers (MAR)
To perform write and read operations, two registers are essential
1. Memory data register (MDR)
2. Memory access registers (MAR)
The MDR are used exclusively by the CPU and are not directly accessible to the programmer
Memory access registers (MAR)
In order to perform a write operation into a specified memory locations, the MDR and MAR are used as follows
- The word to be stored into the memory locations is first loaded by the CPU into MDR.
- The address of the location into which the word is to be stored loaded by the CPU into the MAR.
- A writ signal is then issued by the CPU
Memory access registers (MAR)
Similarly, to perform a memory read operations, the MDR and MAR are used as follows
- The address of the location from which the word is to be read is loaded into the MAR
- A read signal is issued by the CPU
- The required words is then loaded by the memory into the MDR and ready for use by the CPU.
Instructions fetching registers
In order to fetch an instruction for execution, two registers are used, these are
- Program counter (PC)
i) the PC contains the address of the next instruction to be fetched.
ii) After a successful fetch, the PC is updated to point to the next instruction to be executed
iii) In the case of a branch operation, the PC is updated to point to the branch target instruction after the branch is resolved - Instruction registers (IR)
The fetched instructions is loaded in the IR for execution.
Condition registers
- Condition registers/flag are used to maintain status information
- Some architecture contain a special program status word (PSW)
- The PSW contains bits that are set by the CPU to indicate the current status of an executing program
- These indicator are typically for:
i. Arithmetic operations
ii interrupts
iii memory protection information
iv processor status
Memory
- In a computer, memory refers to devices that can store information temporarily or permanently.
- A computer needs storage devices to operate. Some of the major devices are: HDD, CD, ROM, RAM, Floppy disk etc
- The memory of a computer is an array of millions of adjacent cells
- Each cell in a memory is capable of storing a binary (bit), having a value 1 or 0
- These cells are organized in the form of fixed numbers, say n can be dealt with as an entity
