Module 11: External I/O

Question 1

device driver

Answer 1

a separate device driver exists for each device; the device driver is software that interacts with the interrupts generated by its respective hardware component, acting as an interface between the external devices and the OS; the driver usually runs as a process

Question 2

interrupt handler

Answer 2

a separate handler exists for each device that may generate an interrupt; executes (e.g. as a callback function in C) on interrupt; the device driver communicates with the OS through interrupts

Question 3

device controllers

Answer 3

hardware component that receives data from its respective device, stores it locally, and passes it to the device driver; the controller makes sense of signals going in and coming out from the CPU

• device registers: allow the device driver to read and write status of the devices like checking whether a printer is ready or not
  
  • data buffers: enable one to write to the controller, which is then subsequently pushed onto the external devices; any data that we write to the disk, or read from the disk, is first buffered in the data buffers of the device controllers, then can be read by the device drivers

Question 4

port-mapped I/O

Answer 4

special assembly language instructions that allow the device driver to read directly from the external device

Question 5

memory-mapped I/O

Answer 5

reading or writing to particular addresses that correspond to a location in main memory, control register, of address in the data buffer of a specific I/O device

I/O operations at these addresses are automatically converted to corresponding device control registers or data buffers, reducing the burden on the programmer. This technique requires memory caching to be disabled and the MMU to distinguish the I/O requests from legitimate memory accesses

Question 6

direct memory access (DMA)

Answer 6

to avoid involving the CPU in the data transfer between the physical memory and external device, a separate hardware co-processor called the DMA is tasked with handling I/O requests

Question 7

checksum

Answer 7

a sequence of characters, generated by applying cryptographic hash function to data (e.g. in a file)

using the checksum, a system can validate whether different copies of data match

Question 8

ioctl system call

Answer 8

allows your user application to make requests of devices and is typically used for the process of hardware configuration, command line interface, and building upon kernel functionality

Question 9

I/O scheduling

Answer 9

many processes create I/O requests and the I/O scheduler determines the order in which to send these requests to the external devices while preserving interactivity

Question 10

endpoint

Answer 10

remote device capable of communication over a TCP/IP network

Question 11

socket

Answer 11

a network abstraction uniquely identified by an IP address and port number; a network abstraction used to receive and send data from a given endpoint identified by the IP address for the network service identified by the port number

sockets allow inter or intra machine processes to communicate over the network

Question 12

IP address

Answer 12

32 bit number in IPv4

128 bit number in IPv6

used to identify endpoints and their location in the network

Question 13

port number

Answer 13

16-bit integer; ports are associated with the IP address of the machine being used in networking and the type of network protocol being used in the communication

each port is used to handle a different network service so that the machine can execute multiple services and sessions of the same service

port numbers 0- 1023 are reserved for well-known services and port numbers 1024+ can be used by a developer in general applications

Question 14

socket API

Answer 14

common set of functions, data structures, and constants across many OSes used to maintain and interact with sockets

Question 15

socket()

Answer 15

creates a socket

Question 16

bind()

Answer 16

defines the socket port

Question 17

listen()

Answer 17

sets the socket to start listening for data after it has been bound

Question 18

connect()

Answer 18

initiates a connection with another socket

Question 19

accept()

Answer 19

accepts a connection initiated by another socket

Question 20

send(), sendto(), write()

Answer 20

send data flowing out of the socket

Question 21

recv(), recvfrom(), read()

Answer 21

receive data flowing into the socket

Question 22

close(), shutdown()

Answer 22

closing a socket

Question 23

domain name system (DNS)

Answer 23

a protocol used to map hostnames to IP addresses, which is used to identify well-known servers in the network

Question 24

network interface cards

Answer 24

hardware component that connects a machine to the network

Question 25

device drivers for networking

Answer 25

software interrupt handlers for different network interface cards

Question 26

little endian

Answer 26

store lower order bytes in the lowest memory locations

Question 27

big endian

Answer 27

store higher order bytes in the lowest memory locations

Question 28

stream socket

Answer 28

uses TCP as the underlying protocol; connection oriented, such that, providing a two way stream of bytes; guaranteed reliable, at-most once, and in-order delivery

Question 29

datagram socket

Answer 29

uses UDP as the underlying protocol; connectionless, sending individual messages in chunk bytes; no guarantee of reliable, at most once, and in order delivery