Operating System Kernels, CPU Privilege Modes, and Processes

Vocabulary flashcards covering core concepts of CPU instruction types, CPU privilege modes, monolithic vs micro-kernels, operating system components, processes, threads, and traps.

LOAD

A CPU memory instruction that reads data from memory into a register.

ADD

A CPU arithmetic instruction that adds values contained in two registers.

STORE

A CPU memory instruction that writes data from a register to memory.

IN

A device access instruction that reads data from an input/output device, such as an SSD.

OUT

A device access instruction that writes data to an input/output device.

HLT

A CPU shutdown instruction that stops the CPU from spinning.

User mode (U-mode)

An unprivileged CPU execution mode where only non-sensitive instructions (like memory load/store and arithmetic) are permitted.

Supervisor mode (S-mode)

A privileged CPU execution mode that allows both non-sensitive and sensitive instructions (such as device access and HLT), typically reserved for the operating system kernel.

x86 Privilege Rings

A hierarchical privilege architecture in x86 CPUs ranging from Ring 0 (Kernel, most privileged) to Ring 3 (Applications, least privileged).

Principle of least privilege

The design principle stating that software should only possess as much privilege as it strictly needs to provide its function.

Monolithic kernel

An operating system design where all kernel subsystems (such as file systems, memory management, and drivers) run together inside supervisor mode (S-mode).

Micro-kernel

An OS architecture that minimizes kernel functionality and moves most traditional operating system services into separate user-space servers.

Liedtke's Cardinal Rule

A micro-kernel design rule stating that a concept is tolerated inside the microkernel only if moving it outside would prevent implementing required system functionality.

Protected procedural call (PPC)

The communication mechanism between micro-kernel components that involves switching privilege levels, copying arguments or results, and thread blocking.

Nested kernel

An OS design featuring a tiny, highly-privileged security monitor interposed between hardware and a monolithic kernel to enforce security policies.

Kernel

The core component of an operating system that runs in privileged mode and directly interacts with system hardware.

Operating System (OS)

The complete system package composed of the core kernel along with bundled user-level tools, window managers, file explorers, and graphical interfaces.

Program

A static entity consisting of compiled code or executable files stored on disk.

Process

An active, running instance of a program allocated with hardware resources such as CPU execution time and memory space.

Address space

The isolated portion of main memory (DRAM) presented to a specific running process by the operating system.

Thread

An independent execution context within a process that shares the same parent memory space with other threads.

System call

A request made by a user-mode process to the operating system kernel using specialized CPU instructions to perform privileged operations.

Traps

Involuntary execution transitions to the operating system kernel caused by hardware interrupts or process exceptions.

Interrupts

CPU-enabled event notifications asynchronously delivered to the CPU by external hardware devices or internal timers.

Exceptions

Synchronous traps caused by abnormal or illegal operations within a running process, such as division by zero or invalid memory access.