File System Organization

• Computer system organization involves the structure and components that enable efficient task execution and resource management
• Storage structure defines how data is managed, stored, and retrieved, with different storage devices using various methods like magnetic or flash storage
• File systems are methods or structures the OS uses to organize, store, manage, and retrieve data on storage devices, defining how data is stored, classified by file type, named, accessed, and modified

File System Organization

• A file system organizes data into files and directories, serving as an interface between the user and the physical storage device
• It allows users to organize files into directories or folders with a hierarchy and structure
• Each file has a name and attributes like size, permissions, and timestamps
• File contents are stored in blocks or clusters managed by the file system for optimized storage and retrieval

Access Control & Metadata

• The File system controls file access based on permissions, defining who can read, write, or execute a file with different operating systems having different permission models
• Metadata is data about data, including the file name, size, permissions, creation date, last modified date, and physical location, typically stored in a table like an inode or file allocation table (FAT) in older systems
• The File system decides how to allocate and manage storage space for files, dividing storage into blocks or sectors and keeping track of which blocks are in use or free

File System Operations & Types

• The File system is in charge of renaming and moving data across directories, allowing files to be renamed and moved
• Different operating systems use different file systems
• Common file systems include FAT, FAT32 (used by older OS), NTFS (used by Windows OS), and exFAT (Extended File Allocation Table), optimized for flash drives and SD cards
• Storage structure importance
• They facilitate allocation, retrieval, and organization of data in main and secondary storage, which is important for data management in the OS
• Storage structure is also important for resource allocation, allocating storage for resources effectively to meet running processes and application demands

Storage Systems

• Storage systems are organized hierarchically based on speed, cost, volatility, and caching
• Volatility is a crucial aspect of the storage hierarchy, where higher levels (registers, cache) are volatile, and lower levels are non-volatile
• Caching is employed to bridge the speed gap between storage tiers, copying frequently accessed data from slower storage systems into faster memory
• The CPU reduces the time it takes to retrieve frequently used data by employing the caching method
• Main memory (RAM) can act as the last cache for secondary storage, temporarily storing frequently accessed data for faster CPU access
• Storage systems in a hierarchical structure balance speed, cost, and volatility, utilizing caching mechanisms to enhance performance

Memory Hierarchy

• Computer systems have a memory hierarchy with multiple levels of memory with varying access speeds and capacities
• Each level of hierarchy offers varying speed, cost, and capacity. Volatility in the storage hierarchy is determined by the technology used in each level
• Higher levels like main memory (RAM), cache, and registers are volatile for speed and quick access
• Data stored in RAM is temporary and intended for the current processing task
• Lower levels of secondary storage (HDD or SSD) are non-volatile, storing data persistently over the long term
• Hierarchy from fastest/most expensive to slowest/least expensive: registers, cache, RAM, solid state drives, hard disk drives, optical disks, magnetic tape

CPU Registers

• Fastest and smallest storage units located within the CPU, holding data and instructions currently being processed
• Used as temporary storage for data actively being processed, serving as operands for arithmetic, logic, and other CPU operations
• Directly integrated in the CPU, providing fast access times crucial for efficient processing, acting as an intermediate stage between the CPU's internal operations and larger, slower memory systems like RAM

Cache Memory

• Cache is a small but faster form of volatile memory located between the CPU and main memory, serving as a buffer storing frequently accessed data and instructions to reduce access times
• Divided into multiple Levels, with each level providing progressively larger capacity but slower access times compared to registers
• Used to reduce the average time to access data stored in the main memory
• When you visit a website for the first time, your CPU cache stores parts of the instructions that is needed to load and render that webpage
• When the processor needs to read or write a location in the memory or in the main memory it first checks for a corresponding entry in our cache.

Main Memory

• Also known as RAM, it is the primary form of volatile memory in a computer system, holding data and instructions the CPU needs for quick access during program execution
• All program instructions to fulfill a user's request is stored in this RAM
• Offers faster access times compared to secondary storage devices like SSDs and HDDs but is more expensive and has limited capacity

RAM Types and usage

• There are two types of RAM the DRAM and DSRAM
• DRAM is the most common type of RAM used in modern computers, further divided into generations like DDR, DDR2, DDR3, DDR4, and DDR5, each offering improvements in speed, efficiency, and capacity compared to its predecessors
• Requires refreshing of data every few milliseconds to maintain its contents
• Static random access memory is faster and more expensive than DRAM because unlike DRAM, SRAM doesn't require refreshing to maintain the data, making it faster but also more expensive and less dense

SSD

• Volatile memory usage in computer apps include when you open a program, its code and data are loaded into RAM so when you run a program that file is pulled from the RAM.
• SSDs are non-volatile storage devices that use flash memory to store data, offering faster access times and higher reliability than traditional HDDs
• Types include SATA SSDs, NVMe SSDs, M.2 SSDs, and PCIe SSDs
• SATA SSDs use the SATA interface and are commonly found in laptops and desktops
• NVMe SSDs are optimized for flash memory and connect directly to the PCI for faster data transfer speeds
• M.2 SSDs connect directly to the computer's motherboard via the M.2 slot M.2 SSDs can use either the SATA or NVMe interface
• PCIe SSDs connect to the computer's PCIe slots and use the NVMe protocol for high-speed data transfer

SSD use

• Another type of SSDs are Enterprise SSDs, designed for use in data centers and enterprise environment. reliability, performance and endurance are critical
• Consumer SSDs. These are the kind SSDs designed for use in consumer electronics devices such as laptops, desktop and gaming consoles
• Those SSD offer balance of performance, reliability and affordability for mainstream users

Hard Disk Drives

• Magnetic disks commonly known as hard drives use rotating magnetic platters to store data
• They offer relatively slower access times compared to SSDs but provide higher storage capacity at a lower cost
• Cheaper to produce
• Still widely used for secondary storage in computers due to high storage space when you need to store high amounts of data that need to be stored log term.

Optical and Magnetic Storage

• Optical disks (CDs, DVDs, Blu-ray) use laser technology to read and write data stored on the disk surface in the form of pits and lands, offering lower access time and lower storage capacity compared to previous storage
• Optical disks offer large storage capacities with CDs typically storing around 700 MB, DVDs can store up to 4.7GB in a single layer Blu-ray discs can store up to 25GB in single layer or 50GB in dual layer
• Magnetic tape is another form of secondary memory used for long-term data storage, consisting of a thin strip of plastic coated with magnetic material, being sequential access in nature Unlike random access memory or our SSDs that allow for direct access to any location in the memory

Input/Output Structure

• Concerns everything from sending and receiving data to the various computer devices.
• Includes hardware components like ports, controllers, and buses, as well as software components such as device drivers and operating system services that manage and coordinate the flow of data between the CPU and external devices.
• The computers port are usually where external devices are connected.
• In terms of software components, the device drivers For example, if you install a printer on your computer, then you will need a driver that handles structure

Synchronous I/O and Asynchronous I/O

• Describes how the computer system handles the transfer of data between external devices and the system's memory or CPU
• Synchronous I-O happens when an I-O operation is initiated, and the control may return to the user's program after the I-O operation is complete
• Asynchronous process happens when the control can be given back to the user's program without waiting for the completion of this I-O operation.
• Asynchronous
• the control returns to the user program only upon 10 completion
• Which what happens is CPU will stay stuck in a loop waiting when the operation ends
• only one request is processed at a time
• In asynchronous process
• asynchronous I O or the when the control is in asynchronous I O the control returns to the user program
• preventing the CPU from being blocked and allowing it to perform other tasks while waiting for the IOU to finish.
• the key difference
• Synchronous I-O the control blocks the CPU from other applications
• while on the other hand with an asynchronous process the program is not waiting

DMA

• The IO device table or the device status table is used to index and determine the status of each device, If an IO operation completes, the operating system updates the table and entry and triggers an interrupt, signaling the completion of the task
• The Direct Memory Access (DMA) is technique used to improve the efficiency of the data transfer between these external devices and Main memory without involving now the CPU

Single General Purpose Processors and other facts

• The DMA structure mechanism:
• Allows the external devices to transfer the data directly to or from main memory without the CPU's intervention
• In a system utilizing this DMA mechanism the device controller gains direct access to the system memory.
• Single general purpose processors
• Most systems use a single general purpose processors processors or PDAs through mainframes so computer system architecture
• The CPU is a single general purpose processors which is designed to handle a wide range of computing tasks and instructions

Multi processors

• Multi-processors systems are growing in use and importance.
• These multi-processors systems are also known as the parallel systems or a tightly coupled system.
• These systems refer to computer architecture that consists of multiple processors, also known as CPUs or cores
• work together to execute tasks simultaneously these systems are often referred to as a parallel system because the processors are closely interconnected and collaborate on processing tasks.
• The advantages of using multi-processor systems includes the increased throughput and increase handling

Asymmetric vs symmetric

• At systems now you can distribute these requests among its CPUs or cores.
• It allows them to be processed simultaneously
• Meaning the server can serve more users or process more requests in a given amount of time.
• The multiprocessor comes in two types:
• Asymmetric processing
• symmetric Multi-processing
• asymmetric multi-processing system
• processors is assigned specific tasks or
• processors is assigned specific tasks or function
• Handled by the master processor
• processors have equal access to the system's resources and can execute any task or function.