OS Introduction

What was IBM System/360

An early computer system whose operating system could run on different hardware platforms. Resource-management issues nearly bankrupted IBM.

What is an operating system

A program that runs on raw hardware and acts as an intermediary between users and the computer.

What is an extended machine

The OS hides hardware complexity and presents users with an easier-to-use virtual machine.

What is an abstraction layer

A layer that simplifies and hides low-level hardware details from users and programs.

What is the operating system's role as a resource manager

It allocates hardware resources such as CPU time and memory among programs.

What are two potentially conflicting goals of an operating system

Using hardware efficiently and giving maximum performance to each user.

What is the difference between a mechanism and a policy

Mechanisms provide functionality; policies determine which goals are prioritized.

What characterized first-generation computers (1945-1955)

They used vacuum tubes and plug boards.

What are vacuum tubes

Fragile electronic components that consume lots of power, generate heat, and fail often.

What characterized second-generation computers (1955-1965)

They used transistors and batch processing systems.

What advantages did transistors provide

They were more reliable, energy-efficient, and space-efficient than vacuum tubes.

What is a batch system

A system where jobs are collected and processed sequentially without user interaction.

What characterized third-generation computers (1965-1980)

They used integrated circuits and supported multiprogramming.

What are integrated circuits

Chips containing multiple transistors that make computers cheaper and more capable.

What is multiprogramming

Keeping multiple jobs in memory and switching among them to improve CPU utilization.

What characterized fourth-generation computers (1980-present)

The personal computer era enabled by large-scale integration.

What characterized fifth-generation computers (2001-present)

Systems connected by high-speed networks supporting distributed resource management.

What is direct input computing

A system where jobs were manually entered, executed, and results recorded one at a time.

What problem existed with first-generation systems

Large amounts of computer time were wasted while entering jobs and recording results.

What was the goal of early operating systems

To maximize utilization of expensive computer resources.

What role did the IBM 1401 play in batch systems

It read punch cards onto magnetic tape and printed results from output tapes.

What role did the IBM 7094 play in batch systems

It executed jobs stored on input tapes and generated output tapes.

What is the structure of a typical second-generation job

A job control card, program code card(s), and data card(s).

What is spooling

Simultaneous Peripheral Operations On-Line; overlapping I/O of one job with execution of another.

What is the benefit of spooling

It improves CPU utilization by reducing idle time.

What is a limitation of spooling

Only one job is actively executing at a time.

How does multiprogramming share resources

CPU time and hardware resources are divided among multiple jobs.

How does multiprogramming improve performance

If one job waits for I/O, the OS switches to another ready job.

What is interactive computing

Computing that allows users to interact directly with running programs.

What is timesharing

Multiprogramming combined with interactive real-time scheduling.

What is the purpose of timesharing

To give users the illusion that their programs are running continuously.

What is a benefit of timesharing

Faster debugging and shorter turnaround times.

What is a drawback of timesharing

It wastes some CPU time due to frequent context switching.

What is an example of a mainframe operating system

MVS.

What are examples of server operating systems

FreeBSD, Solaris, and Linux.

What is an example of a multiprocessor operating system

Cellular IRIX.

What are examples of personal computer operating systems

macOS, Windows, and Linux.

What is an example of a real-time operating system

VxWorks.

What is a real-time operating system

An OS that guarantees a specified amount of CPU time within a given period.

What is an example of an embedded operating system

Raspbian running on a Raspberry Pi.

What are smart card operating systems

Highly scaled-down operating systems optimized for speed and small size.

What are the main components of a simple PC

CPU, RAM, and device/network controllers.

What is the storage pyramid

A hierarchy of storage technologies with varying capacity and latency.

What is the goal of the storage pyramid

To provide the illusion of large, low-latency memory.

How do latency and capacity change in the storage hierarchy

Latency decreases toward the top while capacity increases toward the bottom.

What is caching

Moving frequently used data into faster storage to improve performance.

What is virtual memory

A memory management technique that creates the illusion of more memory than physically exists.

What is a disk platter?

A circular disk surface used to store data.

How many surfaces can a disk platter have?

Up to two.

What is a track on a disk?

A concentric circle where data is stored.

What is a sector?

A subdivision of a track that stores a fixed amount of data.

What is a cylinder?

The set of corresponding tracks across all disk surfaces.

What is a disk head?

A component that reads and writes data on disk surfaces.

What does an actuator do?

Moves disk heads across tracks.

Why do operating system designers care about disk structure?

File system design is heavily influenced by physical disk layout.

Why is memory protection necessary for multiprogramming?

To prevent one process from interfering with another.

What happens if a process wants more memory than allocated?

It is not allowed to exceed its memory bounds.

What is memory protection?

A mechanism that prevents processes from accessing memory outside their assigned region.

What is a base register?

A register that stores the starting address of a process's memory region.

What is a limit register?

A register that stores the size or upper boundary of a process's memory region.

What is a single base/limit pair?

One set of registers used to define a process's memory range.

What are two base/limit registers used for?

Separating program code and data memory regions.

What advantage do two base/limit registers provide?

Multiple users can run the same code with different data.

What is the hardware sequence of a device request?

Request → Controller → Device → Interrupt Controller → CPU.

What is an interrupt?

A signal indicating that a device requires CPU attention.

What does an interrupt controller do?

Notifies the CPU when an interrupt occurs.

What is an interrupt vector table?

A table that tells the CPU which interrupt-handling routine to execute.

How does the OS create the illusion of multiple programs running?

By rapidly switching the CPU among processes.

What is a process?

A program in execution with its own protected memory context.

What is a thread?

An execution unit that shares memory with other threads in the same process.

What is a process tree?

A structure that tracks parent-child relationships among processes.

What is deadlock?

A situation where processes cannot proceed because each is waiting for resources held by another.

Why is deadlock harmful?

Resources are tied up and no process can make progress.

What is a file system?

A method for organizing and storing files on storage devices.

What is a directory tree?

A hierarchical structure used to organize files and directories.

What is a pipe?

A communication channel that transfers data between processes.

How was a pipe described in class?

A file with no name and no storage space allocated to it.

What is a process's address space?

The memory that a process is allowed to access.

What is a process's state?

The contents of registers and memory associated with a process.

What information is stored in a process state?

Register values, memory contents, the program counter, and stack pointer.

What is a process table?

A data structure used by the operating system to track all active processes.

Can processes create other processes?

Yes, parent processes can create child processes.

What are the three segments of a process?

Text, Data, and Stack.

What is stored in the text segment?

Executable program code.

What is stored in the data segment?

Global variables, static variables, heap memory, and dynamically allocated memory.

What is stored in the stack segment?

Local variables and procedure call information.

Where is memory allocated by malloc() or new stored?

In the data segment (heap).

What is the heap?

The area of memory used for dynamic allocation.

Does the text segment grow?

No.

In which direction does the data segment grow?

Upward in memory.

In which direction does the stack grow?

Downward in memory.

Why do the stack and data segment grow toward each other?

To allow flexible memory usage without preallocating space.

What is a real-world example of deadlock?

Trucks entering an intersection from all directions and blocking each other.

What is interprocess communication (IPC)?

Mechanisms that allow processes to exchange information.

What synchronization issue can IPC create?

Processes may interfere with each other when sharing data.

What are examples of IPC mechanisms?

Networks and pipes.

What is privileged mode?

A CPU mode where the operating system can perform restricted operations.

What operations require privileged mode?

Accessing devices and changing memory allocations.

What is user mode?

A restricted CPU mode where application programs execute.

Why can't user programs directly access hardware?

Those operations require privileged mode.