Exam 1 Review - Chapters 1 to 3, Computer Organization Review, Tutorials 1 and 2

Question 1

What is the simplest way to describe a computer?

Answer 1

HW + OS + Apps + Users

Question 2

What is the user view like?

Answer 2

Single-user, at a terminal/mainframe, uses embedded systems

Question 3

What is system view?

Answer 3

OS is a resource allocator, control program, the one program running at all times (AKA the kernel)

Question 4

What is a bootstrap program?

Answer 4

A program loaded at power-up or reboot, stored in ROM/EPROM, AKA firmware, initializes all aspects of the OS

Question 5

Can I/O devices and the CPU execute concurrently?

Answer 5

Yes, 1/+ CPUs, and device controllers, connect through a common bus providing access to shared memory

Question 6

What do device drivers do?

Answer 6

Provides uniform interface between controller and the kernel

Question 7

How does the OS discover the occurrence of an event?

Answer 7

Through polling (CPU constantly loops to see whether the device is ready) or interrupt (CPU works on other tasks until an interrupt is received)

Question 8

What’s a HW interrupt?

Answer 8

A signal is sent to the CPU

Question 9

What is a SW interrupt?

Answer 9

Known as trap/exception, includes SW errors, requests for an OS service, system call

Question 10

What is the storage hierarchy based on?

Answer 10

Based on speed, cost, volatility

Question 11

How is the storage hierarchy organized?

Answer 11

Magnetic tapes, optical disk, hard disk, SSD, main memory, cache, registers

Question 12

What kind of systems exist concerning processors?

Answer 12

Single-processor (single general-purpose processor with one general-purpose CPU), multiprocessor (can be a multicore system), and clustered (Independent with shared common storage)

Question 13

What kinds of multiprocessor systems exist?

Answer 13

Asymmetric (each processor assigned a specific task, batch processor controls the system) and symmetric (each processor performs all tasks)

Question 14

What is a batch system?

Answer 14

Multiprogramming, users do not interact with the system, organizes jobs so CPU always has one to execute

Question 15

What is time sharing?

Answer 15

Multitasking, users can interact with the system, each user has at least one program executing in memory, if processes don’t fit in memory, swapping moves them in and out to run

Question 16

Describe dual mode operation

Answer 16

User (mode bit = 1) and kernel mode (0), allows OS to protect itself and other system components, kernel mode can only be entered by making system calls and is the only one that can execute certain machine instructions

Question 17

How is a system call implemented?

Answer 17

1) The user’s program makes an indirect system call
2) A number is associated with each system call
3) An entry of the index table points to the detailed implementation of the system call

Question 18

Describe message passing

Answer 18

Suitable for transferring smaller amounts of data (imagine an envelope containing just one letter) and has simpler implementation of communication

Question 19

Describe shared memory

Answer 19

Has a maximum transfer rate but has problems like synchronization and security (imagine sharing a PO box with a friend or even a stranger)

Question 20

Can an OS be perfect and meet all requirements?

Answer 20

No, there is no unique solution for meeting all requirements, must select own personal most important requirements

Question 21

Describe policy and mechanism in terms of principle

Answer 21

Policy is “what will be done?” and mechanism is “How will the policy be implemented?”; Policy is changeable without needing to rewrite code but mechanism is fixed

Question 22

What is a simple structure?

Answer 22

Provides most functionality in least space, no distinction between user and kernel modes, not divided into modules for MS-DOS layered structure; System programs and kernel separated for UNIX partially-layered structure

Question 23

What is a layered approach structure?

Answer 23

OS divided into layers, each built on top of lower layers. Very simple for constructing and debugging but each layer adds overhead to a system call

Question 24

What is a microkernel structure?

Answer 24

Removes all nonessential components from the kernel, and implement them as system applications instead, portable and very secure

Question 25

Describe the command interpreter

Answer 25

A form of emulation, usable as a program such as shell, command line uses argv (arguments vector) and argc (arguments counter)

Question 26

What is the difference between a process and a program?

Answer 26

A process is a program in execution, active, and a program is a passive entity stored in memory as an executable file

Question 27

Describe a process in terms of memory

Answer 27

Has multiple parts: stack (contains temporary data such as function parameters and local variables), heap (used for dynamic memory allocation), data (stores global and static variables), and text (compiled program code)

Question 28

Describe process states (new, ready, running, waiting, terminated)

Answer 28

New (process being created), ready (process waiting to be assigned to a processor), running (instructions being executed), waiting (process is waiting for some event to occur), terminated (process finished execution)

Question 29

What is a process control block (PCB)?

Answer 29

Stores process-specific information, contains: process state, process number, CPU registers and scheduling information, program counter, registers, memory limits, and list of open files

Question 30

Describe the different types of scheduling queues of processes (job, ready, device)

Answer 30

Job queue (set of all processes in the system), ready queue (set of all process residing in main memory, waiting), device queues (set of processes waiting for an I/O device)

Question 31

Difference between long-term (job) scheduler and short-term (CPU) scheduler?

Answer 31

Long-term selects which processes should be brought into the ready queue, infrequently invoked, while short-term selects which process should be executed next and allocates CPU, frequently invoked

Question 32

What is a context switch?

Answer 32

Loads saved state for a new process and saves states of an old process when CPU switches to another process. Is overhead, system does no useful work while switching

Question 33

What is a daemon?

Answer 33

A background process that normally runs indefinitely

Question 34

Describe multiprogramming

Answer 34

The number of processes that are in the memory, maximizes CPU use

Question 35

The difference between I/O-bound and CPU-bound processes

Answer 35

I/O-bound processes spends more time doing I/O and has many short CPU bursts while CPU-bound processes spends more time doing computations and has few long CPU bursts

Question 36

Why is a good process mix of I/O and CPU necessary?

Answer 36

To keep both CPU and devices fully utilized

Question 37

What are zombie processes?

Answer 37

A terminated process whose parent has not yet called wait()

Question 38

What are orphan processes?

Answer 38

An orphan process is a process whose parent process has finished/terminated, though it remains running itself