2.
System Buses Definition:
A system bus is a set of electrical pathways that connect major components of a computer (CPU,
memory, I/O devices) to transfer data, addresses, and control signals.
Types of Buses:
Data Bus: Carries actual data between components (bidirectional).
Address Bus: Carries memory addresses to specify where data is read from or written to (unidirectional).
Control Bus: Carries control signals to manage operations (e.g., read, write, interrupt).
Characteristics:
Bus Width: Number of bits transferred simultaneously (e.g., 32-bit data bus).
Bus Speed: Measured in MHz or transfer rate (e.g., bytes per second).
Operation:
The CPU uses the address bus to select a memory location or I/O device.
Data is transferred via the data bus.
Control signals coordinate timing and operations.
3. Internal Memory – Computer Memory System
(RAM/ROM)Definition:
Internal memory is the primary storage used by the CPU for immediate data access during processing. It
includes RAM and ROM.
RAM (Random Access Memory)Definition:
Volatile memory used to store data and instructions temporarily during program execution.
Types:
1.SRAM (Static RAM):
Uses flip-flops, faster, more expensive.
Used in cache memory.
2.DRAM (Dynamic RAM):
Uses capacitors, needs periodic refreshing, cheaper.
Used in main memory.
Characteristics:
Volatile: Loses data when power is off.
Read/write capability.
Faster than secondary storage but slower than registers.
ROM (Read-Only Memory):
Non-volatile memory that stores permanent data, such as firmware or boot instructions.
Types:
PROM (Programmable ROM): Programmed once after manufacturing.
EPROM (Erasable PROM): Erasable using UV light.
EEPROM (Electrically Erasable PROM): Erasable electrically, used in flash memory.
Characteristics:
Non-volatile: Retains data without power.
Primarily read-only (except in specific cases like EEPROM).
Comparison:
RAM: Volatile, read/write, used for temporary storage.
ROM: Non-volatile, read-only, used for permanent storage.
4. Input and Output Devices - External Devices, I/O Modules, Programmed I/O, Interrupt-Driven I/O,
Direct Memory Access, I/O Channels and Processors, External Interface
Input and Output Devices
Input Devices: Devices that send data to the computer (e.g., keyboard, mouse, scanner).
Output Devices: Devices that receive data from the computer (e.g., monitor, printer, speakers).
Examples:
Input: Touchscreen, microphone, joystick.
Output: Projector, plotter.
Role:
Facilitate interaction between the user and the computer.
I/O Modules
Hardware components that interface between the CPU and I/O devices to manage data transfer.
Functions:
Buffering data.
Error detection and correction.
Converting signals between CPU and device formats.
Example:
A USB controller acts as an I/O module for USB devices.
Programmed I/O Definition:
The CPU directly controls I/O operations, checking device status and transferring data.
Process:
CPU polls the device to check if it’s ready.
Data is transferred via CPU registers.
Drawbacks:
CPU is busy during I/O operations, reducing efficiency.
Suitable for low-speed devices.
Example:
Reading data from a keyboard.
Interrupt-Driven I/O
The device interrupts the CPU when it is ready to send or receive data.
Process:
Device sends an interrupt signal.
CPU pauses current tasks, handles I/O, then resumes.
Advantages:
CPU is free for other tasks until the interrupt.
More efficient than programmed I/O.
Example:
Mouse click triggering an interrupt.
Direct Memory Access (DMA):
A method allowing I/O devices to transfer data directly to/from memory without CPU involvement.
Process:
DMA controller takes over the bus.
Transfers large data blocks directly between device and memory.
Advantages:
Frees CPU for other tasks.
Faster for large data transfers (e.g., video streaming).
Example:
Hard disk transferring data to RAM.
I/O Channels and Processors:
Specialized processors that manage I/O operations independently of the CPU.
Types:
I/O Channel: Handles multiple devices, offloading I/O tasks (e.g., in mainframes).
I/O Processor: More advanced, with its own instruction set for complex I/O tasks.
Advantages:
Enhances system performance by reducing CPU load.
External Interface:
The connection between the computer and external devices.
Types:
Serial Interface: Data transmitted bit by bit (e.g., USB, RS-232).
Parallel Interface: Multiple bits transmitted simultaneously (e.g., printer ports).
Examples:
USB, HDMI(High-Definition Multimedia Interface), SATA (serial advanced technology
attachment, is a computer bus interface used to connect storage devices like hard drives and SSDs to a
computer's motherboard.), Ethernet.
Role:
Ensures compatibility and efficient data transfer between devices.
