CST 334 Week 7 - Home stretch

 1. Topics Covered in Class

·       I/O devices and system architecture

·       Device drivers

·       Device registers and memory-mapped I/O

·       Canonical I/O protocol

·       Polling

·       Interrupts

·       Direct Memory Access (DMA)

·       Blocking vs. non-blocking I/O

·       Hard disk drive (HDD) structure

·       Disk access time (seek time, rotational delay, transfer time)

·       Disk scheduling basics

·       Files

·       Directories

·       Directory hierarchy and pathnames

·       File system interface (open, read, write, close)

·       File descriptors

·       Open file table

·       File offsets

·       File sharing (fork, dup)

·       Inodes

·       File metadata

·       File system layout

·       Data blocks

·       Free space management

·       Bitmaps for free space tracking

2. Explanation of Each Topic

·       I/O Devices and System Architecture - I/O devices allow the computer to interact with the outside world, such as disks, keyboards, and displays. The OS organizes these devices within a layered architecture so slower devices do not block faster components like the CPU and memory.

·       Device Drivers - Device drivers are software components that act as a bridge between the OS and hardware devices. They hide hardware-specific details and provide a consistent interface for the OS.

·       Device Registers and Memory-Mapped I/O - Devices expose control and status registers that the OS reads and writes to communicate with hardware. With memory-mapped I/O, these registers appear as regular memory addresses.

·       Canonical I/O Protocol - The canonical I/O protocol defines a standard way for the OS to communicate with devices: check status, issue commands, and transfer data. This keeps device interaction predictable and structured.

·       Polling - Polling repeatedly checks a device to see if it is ready. While simple, polling wastes CPU time and is inefficient for slow devices.

·       Interrupts - Interrupts allow devices to notify the CPU when they need attention. This lets the CPU do other work instead of constantly checking device status.

·       Direct Memory Access (DMA) - DMA allows devices to transfer data directly to and from main memory without CPU involvement. This improves performance and reduces overhead for large data transfers.

·       Blocking vs. Non-Blocking I/O - Blocking I/O causes a process to wait until the operation completes, while non-blocking I/O allows the process to continue running. This choice affects responsiveness and program design.

·       Hard Disk Drive (HDD) Structure - Hard disks store data on spinning platters divided into tracks and sectors. A moving disk arm reads and writes data, which affects access speed.

·       Disk Access Time - Disk access time includes seek time, rotational delay, and transfer time. Reducing these delays is key to improving storage performance.

·       Disk Scheduling Basics - Disk scheduling determines the order in which disk requests are served. Good scheduling reduces seek time and improves throughput.

·       Files - A file is a persistent, linear sequence of bytes stored on disk. The OS does not interpret file contents, only stores and retrieves them reliably.

·       Directories - Directories map human-readable names to files or other directories. They organize files into a hierarchical structure.

·       Directory Hierarchy and Pathnames - The directory hierarchy starts at the root directory and branches into subdirectories. Pathnames specify the location of files within this structure.

·       File System Interface - The file system interface provides system calls like open, read, write, and close. These calls abstract away low-level disk operations.

·       File Descriptors - A file descriptor is a small integer that represents an open file in a process. It is used by the OS to track file access.

·       Open File Table - The open file table stores information about each open file, including its offset and access mode. Multiple file descriptors can reference the same table entry.

·       File Offsets - A file offset tracks the current position within a file. Each read or write updates this offset automatically.

·       File Sharing (fork, dup) - File sharing allows multiple file descriptors or processes to refer to the same open file table entry. This enables coordinated access to files.

·       Inodes - An inode stores metadata about a file, such as size, permissions, and block pointers. File names are stored separately in directories.

·       File Metadata - Metadata describes file properties rather than contents, including ownership, timestamps, and access permissions.

·       File System Layout - The file system layout divides disk space into regions like the superblock, inode table, and data blocks. This structure enables efficient file management.

·       Data Blocks - Data blocks store the actual contents of files. Inodes point to these blocks to locate file data on disk.

·       Free Space Management - The OS tracks unused disk space so it can allocate blocks to new or growing files. Efficient tracking improves performance.

·       Bitmaps for Free Space Tracking - Bitmaps use bits to represent whether blocks are free or allocated. This allows fast identification of available disk space.

3. Identify least-understood topics — of these topics, which was the hardest for you to write the descriptions?

The topic I had the most difficulty with this week was persistence-related calculations, In theory the calculations seemed easy, but on my first try of the quiz I forgot that everything was supposed to be in milliseconds and not seconds, so my answers were way off. While I understood the concepts themselves, working through the numerical calculations took a little more effort than the conceptual explanations.

4. Explain the nature of your confusion — for these difficult topics, what pieces of them make sense and what pieces are difficult to describe?

I understood how persistent storage works and why disk access time is broken into different parts, but I had a little trouble applying the formulas consistently when calculating total access time. Once I worked through examples step by step, the calculations became clearer.

5. Identify “aha” moments — which topic did you find it easiest to write about, and why did it make sense?

My main “aha” moment came from learning about file descriptors and the open file table. Understanding that a file descriptor is simply an index that points to an entry managed by the OS made file operations much clearer. This helped connect system calls like open, read, and write to what the operating system is actually tracking internally.

6. Ask questions — what do you think will come next? Are there any gaps that don’t seem to be explained yet?

I am curious about how modern file systems improve performance and reliability beyond the basic structures we covered. I would like to learn more about techniques such as journaling, crash recovery, and how file systems handle failures while maintaining data consistency.

7. What connections did you see to other classes and applications — have you used/heard/thought about these topics before?

These topics connect strongly to experiences in programming and IT-related courses, especially when working with files, directories, and storage devices. Concepts like file descriptors and disk access help explain real-world behavior such as slow file operations or system lag during heavy I/O. This material also connects directly to application development, since almost every program relies on file systems and I/O to function correctly.