CSE 120 Operating Systems Principles Lecture 17: Virtual Machines

Flashcards for Operating Systems Principles Lecture 17 focusing on vocabulary.

Crash Consistency Problem

File system operations may involve writing multiple blocks and crashes can happen at any time, possibly leaving the file system in an inconsistent state. Goal: ensure updates occur atomically.

fsck

The file system checker in Unix that scans the file system for inconsistencies when the system boots and attempts to repair them or notify an administrator.

Ordered Writes

A method to prevent file system inconsistencies by writing blocks to disk in a specific, safe order, such as initializing blocks before writing pointers to them.

Journaling (Write-Ahead Logging)

A technique where changes to the file system are first recorded in a special append-only log file (the journal) before being applied to the main file system.

Journal

An append-only file containing log records of file system transactions, including transaction IDs, block addresses, and commit records.

Checkpointing

In journaling, it involves recording the current position in the log, copying modified blocks to their final destinations, and then clearing the log before the recorded position.

Virtual Machine (VM)

An abstraction that provides an environment with virtualized hardware, allowing guest operating systems to run as if they have full control of the underlying hardware.

Virtual Machine Monitor (VMM) / Hypervisor

Software that virtualizes an entire physical machine, presenting a hardware interface to guest OSes, managing resources, and isolating VMs from each other.

Trap-and-Emulate

A VMM approach where guest OS actions that require privilege cause a trap to the VMM, which then simulates the appropriate behavior before returning control to the guest OS.

Type 1 Hypervisor (Bare Metal)

A hypervisor that runs directly on the hardware, without an underlying host OS.

Type 2 Hypervisor (Hosted)

A hypervisor that runs on top of a host operating system.

Paravirtualization

A virtualization technique where the guest OS is modified to cooperate with the VMM, often through a hypervisor API, to improve performance.

Binary Translation

A virtualization method where guest OS code is rewritten at runtime to replace privileged instructions with emulation code, often trapping to the VMM.

Full Virtualization

Virtualization without modification of guest OS.