Lecture 5
Tehreem Tajammal
Spooling
• Spooling (Simultaneous Peripheral Operations On-Line)
• Used in devices like printers, where data is temporarily stored in a queue
before processing.
• Allows CPU to keep working while the device processes data in the
background.
• Example: Print spooler in Windows handles multiple print jobs efficiently.
• ✅ Advantage: Increases system performance by allowing parallel
processing
Buffering
• Temporary memory storage that holds data before processing.
• Used in audio/video streaming, file transfers, and keyboard inputs.
• Example: Video buffering on YouTube ensures smooth playback.
• ✅ Advantage: Reduces delays and manages data transfer efficiently.
Real-Time Operating System
• A Real-Time Operating System (RTOS) processes tasks within a guaranteed time
frame, which is very important for time-sensitive applications.
• Types of Real-Time Systems:
• Hard Real-Time Systems – Strict deadlines must be met.
• Example: Aircraft control systems, pacemakers.
• Soft Real-Time Systems – Deadlines are important but not critical.
• Example: Multimedia streaming, online gaming.
• ✅ Advantage: RTOS ensures predictable and timely responses, making it
ideal for critical operations where every second counts.
Booting Mechanism
• process of starting a computer by loading the kernel
• A small piece of code known as the bootstrap program or boot loader locates the
kernel.
• The kernel is loaded into memory and started.
• The kernel checks and ensures that all the hardware devices are connected
(keyboard, mouse, screen, etc.).
• Mount Root File System: The OS then connects to the main storage system (like
your hard drive or SSD) where files and programs are stored.
Cont…
• Some computer systems use a multistage boot process: When the computer is first
powered on, a small boot loader located in nonvolatile firmware known as BIOS is run.
• This initial boot loader usually does nothing more than load a second boot loader,
which is located at a fixed disk location called the boot block.
• The program stored in the boot block may be sophisticated enough to load the entire
operating system into memory and begin its execution.
• More typically, it is simple code (as it must fit in a single disk block) and knows only the
address on disk and the length of the remainder of the bootstrap program.
Cont…
• Many recent computer systems have replaced the BIOS-based boot process with UEFI (Unified
Extensible Firmware Interface). UEFI has several advantages over BIOS, including better support for
64-bit systems and larger disks. Perhaps the greatest advantage is that UEFI is a single, complete
boot manager and therefore is faster than the multistage BIOS boot process. Whether booting from
BIOS or UEFI, the bootstrap program can perform a variety of tasks. In addition to loading the file
containing the kernel program into memory, it also runs diagnostics to determine the state of the
machine —for example, inspecting memory and the CPU and discovering devices. If the diagnostics
pass, the program can continue with the booting steps. Then bootstrap can also initialize all aspects of
the system, from CPU registers to device controllers and the contents of main memory. Sooner or
later, it starts the operating system and mounts the root file system. It is only at this point is the system
said to be running.
GRUB
GRUB is an open-source bootstrap program for Linux and UNIX systems.
• It runs at startup before the OS.
• Reads settings from a configuration file.
• Let's you choose between different OS or kernels.
• You can edit boot options and kernel parameters during boot.
It’s flexible, helpful for troubleshooting, and supports dual-boot
systems like Linux and Windows.
Linux Kernel
When Linux starts:
1. The kernel image is compressed to save space and load faster.
2. The bootloader loads it into memory and sets up a temporary RAM file system
called initramfs.
[Link] contains important drivers needed to access the real file system.
4. Once the real file system is ready, Linux switches from RAM to the actual file system.
5. Then, it starts the first system process and launches other services (like web
servers).
6. Finally, it shows the login screen to the user.
