Lesson 1

Question 1

What is an OS

Answer 1

Software that manages a computers hardware. Provides interface between the computer user and the computer hardware

Question 2

What is a resource allocator?

Answer 2

the OS acts as a manager of CPU, memory, storage, IO

Question 3

What is a control program?

Answer 3

manages the execution of user programs to prevent errors and improper use of the computer. Especially with IO devices

Question 4

What is a bus?

Answer 4

provides access between components and shared memory

Question 5

What is a device controller?

Answer 5

maintains local buffer storage and set of registers. responsible for moving data between peripherals and local buffer storage

Question 6

what is a device driver?

Answer 6

driver understands the device controller and provides the OS with an interface to the device

Question 7

what is an interrupt?

Answer 7

hardware can trigger an interrupt at any time by sending a signal to the CPU on the system bus (usually)

Question 8

what is an interrupt vector?

Answer 8

a list of addresses (pointers) to the interrupt

Question 9

high level explanation of interrupt flow

Answer 9

CPU uses interrupt-request line that the CPU checks after executing every instruction, when CPU detects an interrupt it reads the number and jumps to the pointer in the interrupt vector. then returns with “return_from_interrupt”

Question 10

how does the CPU know which interrupts to prioritize?

Answer 10

interrups have interrupt priority levels

Question 11

What is the difference between main and secondary memory?

Answer 11

main memory is ram, secondary is storage devices like HDD’s, ssd’s, etc

Question 12

what is direct memory access? (DMA)

Answer 12

Used for bulk movement of data, basically copies entire blocks of memory of data directly to or from the devices and main memory, only requires 1 interrupt

Question 13

how do clustered systems work?

Answer 13

utilize SAN’s and distributed lock managers to perform compute across shared stroage (think database)

Question 14

What is a process?

Answer 14

programs that are organized so that the CPU always has one to execute in a multiprogrammed system

Question 15

how do multiprogrammed systems works?

Answer 15

the OS keeps several processes in memory simultaneously and works on them switching back and forth when IO is needed

Question 16

what are the two modes provided by the OS?

Answer 16

User mode and Kernel mode

Question 17

What is the purpose of dual-modes in the OS?

Answer 17

to ensure that programs cannot cause other programs to execute incorrectly

Question 18

What mode do system calls execute in?

Answer 18

kernel mode

Question 19

When exceptions or interrupts occur, which mode does the OS switch into?

Answer 19

kernel mode

Question 20

what is a mode bit?

Answer 20

a bit that designates whether the OS is in kernel or user mode

Question 21

describe what happens when a syscall is executed?

Answer 21

treated as a software interrupt, control is passed through the interrupt vector to a service routine in the OS and mode bit is set to kernel. the kernel examines the interrupt and calls the syscall

Question 22

what is a timer used for?

Answer 22

to ensure that a user program doesn’t get stuck in an infinite loop or fail to give control back to the OS

Question 23

what is a program counter?

Answer 23

keeps a list of next instructions to execute

Question 24

what is the difference between processes and user programs?

Answer 24

programs are passive, processes are active

Question 25

What is the OS responsible for when it comes to memory?

Answer 25

Keeps track of memory being used, allocates and deallocates memory, moves processes in and out of memory