OS for Programmers (my set)(OG)

Constant Linear Velocity (CLV)

• Variable speed of the disk.

• Bit density stays constant from inner to outer tracks.

• The disk spins faster on the inner tracks and slows down on the outer tracks, ensuring even spacing of data regardless of the track's position

Constant Angular Velocity (CAV)

• Constant speed of the disk.

• Bit density decreases from inner to outer tracks.

• The disk doesn't change its speed, which is simpler mechanically, but the amount of data you can store and retrieve changes based on the track position.

Two stages of Positioning Time (Random-Access Time)

Seek Time and Rotational Latency

Seek Time

the time it takes the read-write head to position over the desired cylinder.

Rotational Latency

the time it takes the read-write head, once over the desired cylinder, to access the desired track

Raw Disk

Direct access to a secondary storage device as an array of blocks with no file system.

Boot Disk

A disk that has a boot partition and a kernel to load to boot the system. A device that has a boot partition and can store an operating system for booting the computer.

System Disk

A storage device that has a boot partition and can store an operating system and other information for booting the computer.

Virtual Disk

Simulates a disk drive using part of another storage device (like in virtual machines)

Bootstrap

The set of steps taken at computer power-on to bring the system to full operation

Boot Partition

A storage device partition containing an executable operating system

Swapping

A memory management technique where entire processes are moved between main memory (RAM) and secondary storage (disk) to free up physical memory.

Memory Compaction

When the operating system rearranges data in memory to combine scattered empty spaces (or "holes") into one big empty space. This helps free up a large enough block of memory for new processes, instead of leaving memory fragmented into small, unusable pieces.

Preemptive Scheduling

Stops a currently running process and allows the system to pick another process to run.

Non-Preemptive Scheduling

Once a process starts running, it keeps running until it finishes or voluntarily gives up the CPU. It won’t be stopped in the middle

Short Term Scheduler (CPU Scheduler)

Decides which process runs on the CPU next, and it can be preemptive (interrupt processes) or non-preemptive (let processes finish)

Long Term Scheduler (Job Scheduler)

Decides which processes get admitted into the system to run at all.

Bitmap

A bitmap is an array of bits where each bit represents the status of a disk block.

• 1 means the block is allocated (in use).

• 0 means the block is free (available for use).

Rotational Delay (Latency)

Waiting for the disk to rotate so the desired data is under the head.

Sector Overhead Time

The small, additional time spent handling administrative data associated with a sector on a hard disk

Partitioning

Creating groups of blocks on secondary storage

Digest

The output or result produced by a hash function

Login Spoofing

Type of attack where an attacker creates a fake login prompt

Back Door

A mechanism that bypasses user authentication. Ex: A systems programmer could modify the login utility to accept a specific user without requiring a password, thus permitting unauthorized access to the system at a later time.

Blocking

A mode of communication in which the sending process is blocked until the message is received by the receiving process or by a mailbox and the receiver blocks until a message is available. In I/O, a request that does not return until the I/O completes.

Non-Blocking

A type of I/O request that allows the initiating thread to continue while the I/O operation executes. In interprocess communication, a communication mode in which the sending process sends the message and resumes operation and the receiver process retrieves either a valid message or a null if no message is available. In I/O, a request that returns whatever data is currently available, even if it is less than requested.

.Logic Bomb

Unauthorized code inserted into the system and executed at a specified time to perform some destructive action (often for blackmail/revenge)

Information Leaking

The disclosure of confidential or secret information by a legitimate user to an unauthorized user.

Virus

A piece of executable code that embeds itself into legitimate programs and copies itself to other programs and systems with the intention of causing harm

Phishing

An unsuspecting user is presented with a fake webpage that looks like a legitimate site. Can be attempted from outside of the system using email or other means of communication.

Kernel

Minimal set of functions necessary to manage the system resources safely and efficiently

Paging

Translates logical pages to physical frames, allowing non-contiguous memory allocation with equal-sized units.

Dynamic Linking

Loading external libraries or modules at runtime, only when needed, to save memory and allow code sharing among processes.

Static Linking

Including all external libraries or modules in the executable at compile time, resulting in a larger file that uses more memory.

Dynamic Linking Library (DLL)

A file format used to store shared code, functions, and resources that can be used by multiple programs

50% Rule

In dynamic memory allocation, fragmented memory is about 50% of the allocated memory, resulting in one-third of total memory being lost to fragmentation

Linked List

linear data structure where elements, called nodes, are connected using pointers.

Probe

A location to which DTrace can bind a request to perform a set of actions

Belady’s Anomaly

More frames can end up equating to more page faults

Resource Allocation

Operating system service that ensures the efficient operation of the CPU, memory, and I/O

Communications

This service manages the exchange of data between processes or devices, facilitating interaction within the system.

Program Execution

The process of loading, running, and managing programs, allowing them to execute instructions in the CPU.

Distributed Processing

Emerged around the 4th and 5th generations, involving networked systems that share resources and collaborate on tasks.

Batch Processing

Introduced in the 2nd generation of computers, this processing method groups jobs together and runs them sequentially without user interaction

Real-Time Processing

Characterized by continual input, which must be processed fast enough to generate nearly instantaneous output. Each arriving input item is subject to a deadline

Interactive Processing

Allows users to directly interact with the system, responding to user inputs quickly. Became prominent in the 3rd generation.

Daemon

A background process that is part of the OS, responsible for tasks like scheduling, network management, and printing, ensuring services run smoothly.

Worm

An unauthorized program, which exploits one or more systems weaknesses to spawn copies of itself on other systems via computer networks

Typical objective is to cause harm to the system by destroying information or causing denial of service. A buffer overflow attack is a common approach for this to enter a system.

Virus

A piece of executable code that embeds itself into legitimate programs and copies itself to other programs and systems with the intention of causing harm

A Trojan horse attack is a common way for this to enter into a system as part of a service program downloaded by a user from the Internet

Master Boot Record (MBR)

Windows boot code, stored in the first sector of a boot partition

Boot Sector

The first sector of a Windows boot device, containing the bootstrap code

Bootstrap

The set of steps taken at computer power-on to bring the system to full operation

Mounting

Making a file system available for use by logically attaching it to the root file system.

Segmentation

Translates logical segments to physical segments, supporting non-contiguous allocation with variable-sized units.

Frames

Fixed-size physical memory blocks that correspond to logical pages, ensuring non-contiguous allocation in paging systems.

Page Table

A data structure that maps logical pages to physical frames, enabling the OS to translate logical addresses into physical addresses.

Semaphore

A synchronization primitive that controls access to the critical section. It can be a binary …(also called a mutex), which takes values of 1 (available) or 0 (occupied), ensuring mutual exclusion.

Queue

A data structure that maintains the order of processes, typically used to manage tasks waiting for resources

Contiguous Allocation

Stores files in adjacent blocks, requiring continuous space. Fast access but prone to external fragmentation

Linked Allocation

Uses a linked list of blocks, where each block points to the next. Allows files to grow non-contiguously

Indexed Allocation

Uses an index block to hold pointers to all file blocks. Supports random access and non-contiguous storage

Clustered Allocation

Groups blocks into clusters for file storage, reducing the number of disk accesses and improving speed

Multiprogramming

Increases CPU utilization, keeps the CPU busy by switching between processes, ensuring that the CPU doesn't sit idle.

Application Programming Interface (API)

A set of commands, functions, and other tools that can be used by a programmer in developing a program

Common Internet File System (CIFS)

A network file-sharing protocol used to allow users to access files on a remote server over a local network, commonly used in Windows environments

Network Attached Storage (NAS)

A dedicated storage device connected to a local network that provides file-based storage to multiple users and devices

Storage Area Network (SAN)

A local-area storage network allowing multiple computers to connect to one or more storage devices

Multilevel Feedback Queue

Uses multiple queues with different priorities and allows processes to move between queues based on behavior (e.g., CPU usage).

Rotation Delay (Latency)

The time to wait for the desired data item to pass under the r/w head

Track

One of many concentric rings on a magnetic disk surface

Sector

A portion of a track and is the smallest unit of data that can be read or written with a single r/w operation

Salting

Used to prevent efficient brute-force attacks and the use of precomputed hash tables, making it more challenging for attackers to crack hashed passwords.

Swap Space

A dedicated area on the disk reserved for temporary storage of swapped-out processes. Acts as an extension of main memory.

Inode

In many file systems, a per-file data structure holding most of the metadata of the file. The FCB in most UNIX file systems

Device Driver

Device-specific program that implements I/O operations, requested by user applications or the OS, by interacting with the device controller

Device Controller (Adapter)

An electronic circuit capable of operating a specific I/O device using binary signals

Programmed I/O (PIO)

A method of transferring data between a CPU and a peripheral device in which data are transferred one byte at a time

Interrupt

A hardware mechanism that enables a device to notify the CPU that it needs attention

Direct Memory Access (DMA)

A resource-conserving and performance-improving operation for device controllers allowing devices to transfer large amounts of data directly to and from main memory

Trap

A software interrupt. The interrupt can be caused either by an error (e.g., division by zero or invalid memory access) or by a specific request from a user program that an operating-system service be performed

Host-Attached Storage

Storage accessed through local I/O ports. These ports use several technologies, the most common being SATA, as mentioned earlier. A typical system has one or a few SATA ports

Polling

A technique to determine whether a device is busy or idle by reading a flag set and reset by the device controller