A basic computer system consists of what? (6)
- CPU
- System Clock
- Primary Memory (RAM)
- Secondary Memory (SSD or HDD)
- Peripheral I/O Devices
- Bus
Computer System Elements Diagram
Check Notes
What does the CPU do?
- Executes instructions (i.e. a program)
- Controls the transfer of data across the bus
Where is the CPU contained?
On a single microprocessor chip
3 Main Parts of a CPU
- Control Unit (CU)
- Arithmetic Logic Unit (ALU)
- Registers
What does the CU do?
The CU directs the execution of instructions
- Loads an opcode from Primary Memory into Instruction Register (IR)
- Decodes the opcode to identify the operation
- If needed, transfers data between PM and Registers
What does the ALU do?
The ALU performs arithmetic and logical operations on data stored in registers
What are Registers?
They are binary storage units in the CPU
What may Registers contain?
- Data
- Addresses
- Instructions
- Status Information
What are General-purpose Registers used for?
To temporarily hold data and addresses
What does the Program Counter (PC) contain?
It contains the address in memory of the currently executing instruction
It is incremented to execute the next instruction
What does the Status Register (SR) contain?
It contains information (flags) about the result of a previous instruction (e.g. overflow or carry)
What does the System Clock do?
It generates a clock signal to synchronize the CPU and other clocked devices
- It is a square wave at a particular frequency
- Device coordinate on the rising or falling edges
Features of Primary Memory?
- RAM (any byte in memory can be accessed directly if you know its address)
- Can be written to and read from
- Is volatile (Data disappears when powered off)
- Is used to store program instructions and data (variables)
- Consists of a sequence of addressable memory locations (each location is typically one byte long)
Two architectures and features
- In a VON NEUMANN ARCHITECTURE, RAM contains both data and programs
- In a HARVARD ARCHITECTURE, it uses separate memories for data and programs
What is the Bus and what does it do?
The Bus is a set of parallel data/signal lines
It is used to transfer information between computer components
The bus is subdivided into what?
- Address Bus
- Data Bus
- Control Bus
What does the Address Bus do?
The Address Bus specifies memory location in RAM
or sometimes a memory-mapped I/O device
What is the Data Bus used for?
The Data Bus is used for bidirectional data transfer
What is the Control Bus used for?
The Control Bus is used to control or monitor devices connected to the Bus
e.g. read/write signal for RAM
Features of Secondary Memory?
Usage?
Volatility?
Embodied on?
- Is used to hold a computer’s file system (Stores files containing program or data)
- Is non-volatile read/write memory (Its contents persist through power cycle)
- Usually embodied on a HDD or SSD
What do Peripheral I/O Devices do?
They allow communication between the computer and the external environment
e.g. I/O devices are HDD, Modem
Basic CPU Architectures Diagram
Check Notes
Explaining the Basic CPU Architecture Diagram
- Operands for an instruction come from the Accumulator Register (ACC) and from a single location in RAM
- ALU results are always put into the ACC
- Only Load and Store instructions can access RAM
- Other instructions operate on Specified Registers in Register file, not on RAM (b/c registers are more quickly access than RAM, so faster)
