Operating Systems & Parallel Architecture: Process Management & LDE

Comprehensive vocabulary flashcards covering operating systems topics including process creation, states, limited direct execution, system calls vs. libraries, hardware privilege modes, and file redirection.

Shebang (#!)

A mechanism placed on the first line of an executable script that designates the interpreter to use, allowing interpreted programs to be executed directly like machine language binaries.

Limited Direct Execution (LDE)

An operating system approach where user programs run directly on the physical CPU for performance, while the OS retains control and protection via hardware-enforced privilege modes, traps, and interrupts.

Supervisor Mode (Kernel Mode)

A privileged execution mode (indicated when the status register mode bit is $0$) where the CPU can execute all instructions, access all physical memory addresses, and manage system hardware.

User Mode

A restricted processor execution mode (indicated when the status register mode bit is $1$) that prevents processes from accessing arbitrary physical addresses or issuing privileged instructions directly.

Trap

A synchronous software-initiated instruction executed by a user program to switch the CPU from user mode to supervisor mode and request an operating system service.

Interrupt

An asynchronous hardware-generated signal that causes the CPU to pause execution, switch to supervisor mode, and transfer control to an interrupt service routine.

Program Counter (PC) interrupt save

The hardware step during an interrupt where the current instruction address is preserved so the CPU can resume normal execution of the interrupted program later.

Status Register (SR) interrupt save

The hardware step during an interrupt where CPU flags and the current mode status are stored prior to zeroing out the register to switch into supervisor mode.

exec() System Call

A system call that loads and runs an executable file by completely replacing the calling process's current memory, code, and address space; it never returns if successful.

fork() System Call

A system call invoked by a shell or parent process to create an exact duplicate child process for running a program.

Process State: Running

The active state where a process is currently assigned to and executing instructions on the physical CPU.

Process State: Ready

The state where a process is loaded in memory and prepared to execute immediately once chosen by the operating system scheduler.

Process State: Blocked

The state where a process cannot execute because it is waiting on an external event, such as file I/O completion or a timer expiration.

Process State: Zombie

The state of a process that has finished execution via an exit call but still holds an entry in the process table until its parent reaps it.

Process State Transition Diagram

A finite-state model representing how processes move between Ready, Running, and Blocked states via scheduling, preemption, blocking, and unblocking, eventually transitioning to Zombie via exit and deletion via reap.

Process Open File Table Isolation

The security requirement that file descriptor tables must reside in protected kernel space rather than user-writable memory so processes cannot forge descriptors or bypass access controls.

Shell Redirection (a > b)

A shell command execution pattern where standard output is reassigned by executing close(1), followed by open("b" for writing) in the child process before invoking exec(a).

Memory Management Unit (MMU)

A critical hardware unit that translates virtual memory addresses to physical memory addresses and prevents unauthorized cross-process or kernel memory corruption.

putchar() Library Buffering

The standard C library optimization where individual character outputs are stored in a user-space memory buffer to amortize the high overhead of write() system calls.

sleep() System Call Rationale

The design requirement that pausing process execution must be handled as a kernel system call because only the OS scheduler has the authority to deschedule and block a process.

End-of-File (EOF) read() Semantics

The condition indicated when the read() system call returns a value of $0$ bytes, demonstrating that the entire file has been processed.

Virtual-to-Physical Memory Namespace

A linked namespace structure mapping virtual address space pages accessible by a user process to physical RAM frames managed by the MMU.

File Name to Disk Block Namespace

A hierarchical filesystem namespace that maps human-readable directory string names directly to the underlying physical disk blocks storing data.

File Descriptor to Open File Structure Namespace

A per-process namespace mapping small non-negative integer indices (file descriptors) to global operating system open-file data structures.