Computer Systems Notes

Main or Primary Memory: Commonly referred to as 'memory.' It is an essential component where programs and data are loaded before processing. The CPU interacts directly with primary memory. Types include:
- RAM (Random Access Memory): Volatile; data is retained as long as power is supplied.
- ROM (Read Only Memory): Non-volatile; contents are not lost when power is off; used for startup programs (boot loader).
- Cache Memory: A very high-speed memory placed between the CPU and primary memory. Stores copies of frequently accessed data from primary memory.
Secondary Memory (Storage Device): Auxiliary memory for permanently storing data or instructions. Non-volatile with larger storage capacity than primary memory but slower and cheaper than main memory. Examples include HDD, CD/DVD, Memory Card, SSD, Pen Drives.

Computer systems use binary numbers to store data.
Binary digits (0 and 1) are called bits.
- 4 bits = Nibble (e.g., 1001)
- 8 bits (two nibbles) = Byte (e.g., 01000110)
Units of memory:
- KB (Kilobyte) = $1024$ Bytes
- MB (Megabyte) = $1024$ KB
- GB (Gigabyte) = $1024$ MB
- TB (Terabyte) = $1024$ GB
- PB (Petabyte) = $1024$ TB
- EB (Exabyte) = $1024$ PB
- ZB (Zettabyte) = $1024$ EB
- YB (Yottabyte) = $1024$ ZB

Data Transfer Between Memory and CPU: Data is transferred between CPU and primary memory and between primary and secondary memory.
Bus: Data transfer uses physical wires called a bus.
- Data bus: Transfers data between components (bidirectional).
- Address bus: Transfers addresses between CPU and main memory (unidirectional).
- Control bus: Communicates control signals between components (unidirectional).
- System bus: Collectively, these buses make up the system bus.
The CPU places the address of the memory location on the address bus to read or write data.
The CPU specifies read or write control signals through the control bus.
Memory Controller: A memory controller manages the flow of data into and out of the computer's main memory.

A processor (CPU) implemented on a single microchip.
Microprocessors carry out data processing, arithmetic, and logical operations.
Built over integrated circuits with millions of components like resistors, transistors, and diodes.
Evolution: increased processing capability, decreased physical size, reduced cost.
Capable of processing millions of instructions per millisecond.
Microprocessor Specifications:
- Word Size: The maximum number of bits a microprocessor can process at a time.
- Memory Size: The size of RAM varies depending on the word size.
- Clock Speed: The number of pulses generated per second (measured in GHz).
- Cores: Basic computation units within the CPU (dual-core, quad-core, octa-core).

A small computing device with a CPU, RAM, ROM, and other peripherals embedded on a single chip.
Examples: Keyboard, mouse, washing machine, digital camera, pendrive, remote controller, microwave.
Designed for specific tasks, reducing size and cost.
Embedded in devices or systems to perform specific functionality.
Enable automation of repetitive tasks without human intervention.

Data: Raw, unorganized facts that are processed to get meaningful information. A computer considers everything as data.
Data and Its Types: Data can be input in various forms, internally stored in binary form (0 and 1).
- Structured Data: follows a strict record structure, organized in row/column format, easily understandable (e.g., monthly attendance records).
- Unstructured Data: Not organized in a pre-defined format (e.g., audio and video files, text documents).
- Semi-structured Data: No well-defined structure but maintains internal tags (e.g., email, HTML page).

Data Capturing: Gathering data from different sources in a digital form (e.g., keyboard, barcode readers, social media posts).
Data Storage: Storing captured data for later processing (e.g., digital storage devices).
Data Retrieval: Fetching data from storage devices for processing.

Deleted data can be recovered if not overwritten.
Concerns: unauthorized deletion and unwanted recovery.
Mitigation: Limit access, use passwords, encrypt files, and use proper tools to delete or shred data.

A set of instructions that operates the hardware. Without it the hardware components cannot function.
Need of Software: Makes computer hardware useful and operational. Acts as an interface between users and hardware.
System Software: Provides basic functionality to operate a computer (e.g., operating systems, system utilities, device drivers).
- Operating System: Manages computer operations, resources, access, and security (e.g., Windows, Linux, Android, iOS).
- System Utilities: Used for maintenance and configuration (e.g., disk defragmentation tool, anti-virus software).
- Device Drivers: Ensures proper functioning of a particular device; acts as an interface between the device and the operating system.
Programming Tools: Used for writing instructions (code) for the computer. Includes programming languages and language translators.
Application Software: Meets specific user requirements (e.g., word processing, video playback).
- General Purpose Software: Developed for generic applications (e.g., LibreOffice, Adobe Photoshop).
- Customized Software: Tailor-made for specific organizations or individuals (e.g., websites, school management software).

Free and Open Source Software (FOSS): Source code and software are freely available (e.g., Ubuntu, Python).
Freeware: Software is freely available, but the source code may not be available (e.g., Skype, Adobe Reader).
Proprietary Software: Software purchased from a vendor with copyright (e.g., Microsoft Windows, Tally, Quickheal).

A resource manager managing hardware resources, application software, and device drivers.
Objectives: provides services for building and running applications and provides the user interface.

Command-based Interface: Requires entering commands (e.g., MS-DOS, Unix).
Graphical User Interface (GUI): Uses icons, menus, and visual options (e.g., Microsoft Windows, Ubuntu, Macintosh).
Touch-based Interface: Uses touch input (e.g., Android, iOS, Windows 8.1 and 10).
Voice-based Interface: Uses voice commands (e.g., iOS (Siri), Android (Google Now), Windows 10 (Cortana)).
Gesture-based Interface: Uses gestures like waving, tilting, and eye motion (smartphones and laptops).

Process Management: Manages and allocates CPU resources to processes.
Memory Management: Allocates and frees memory to running processes.
File Management: Creates, updates, deletes, and protects files in the secondary memory.
Device Management: Manages I/O devices and hardware connected to the computer system.