CNIT 176 Exam 2

What is a basic model

It is a processing speed or program execution

It is determined primarily by ability of I/O operations to stay ahead of processor

What are I/O requirements

• Means for addressing different peripheral devices

• A way for peripheral devices to initiate communication with the CPU

• An efficient means of transferring data directly between I/O and memory for large data transfers since programmed I/O is suitable only for slow devices and individual word transfers

• Buses that interconnect high-speed I/O devices with the computer must support high data transfer rates

• Capability of handling devices operating at varying speeds with varying delays

• Means for handling devices with extremely different control requirements

Simple I/O configurations

What is a Northbridge in relation to I/O

Special chip to handle communication between CPU, GPU, and RAM

What is a Southbridge in relation to I/O

Special chip to handle communication between northbridge and interfaces such as the USB and SATA (harddrive) interfaces

More Complex I/O Module, Intel Xeon

Separate IO controller chips might have been present for Ethernet, Audio, if not part of Southbridge

Is the northbridge apart of the CPU in the Intel Core Series

True

The northbridge is now part of the CPU

What are different advanced I/O techniques

• Programmed I/O

  • CPU controlled I/O

• Interrupt Driven I/O

  • External input controls

• Direct Memory Access Controllers

  • Method for transferring data between main memory and a device that bypasses the CPU

Programmed I/O

• I/O data and address registers in CPU

• One word transfer per I/O instruction

• Address information for each I/O device

• Full instruction fetch/execute cycle

What are the primary uses of programmed I/O

Keyboards

Communication with I/O controllers

What are interrupts

Signal that causes the CPU to alter its normal flow of instruction execution

• Frees CPU from waiting for events

• Provides control for external I/O initiation

What are examples of interrupts

• Unexpected input

• Abnormal situation

• Illegal instructions

• Multitasking, Multiprocessing

Interrupt Terminology

• Interrupt lines (hardware)

• Interrupt requests

• Interrupt handlers

• Context

What are interrupt lines

One or more special control lines to the CPU

What are interrupt handlers

Program that services the interrupt

What are interrupt handlers also known as

Interrupt routine

Device driver

What is context (in relation to interrupt terminology)

Saved registers of a program before control is transferred to the interrupt handler

Allows program to resume exactly where it left off when control returns to interrupted program

What are different uses of interrupts

• Notify that an external event has occurred

  • Real-time or time-sensitive

• Signal completion

  • Printer ready or buffer full

• Allocate CPU time

  • Time sharing

• Indicate abnormal event (CPU originates for notification and recovery)

  • Illegal operation, hardware error

• Software interrupts

The CPU - The Interrupt Cycle

What is servicing the interrupt

• Lower priority interrupts are held until higher priority interrupts are complete

• Suspend program in progress

• Save context, including last instruction executed and data values in registers, in the PCB or the stack area in memory

• Branch to interrupt handler program

Print Handler Interrupt

Using an interrupt for Time Sharing

What are the different interrupt processing methods

• Vectored interrupt

• Polling

What is vectored interrupt

• Address of interrupting device is included in the interrupt

• Requires additional hardware to implement

What is polling

• Identifies interrupting device by polling each device

• General interrupt is shared by all devices

What do vectored interrupts look like

What do polled interrupts look like

What do multiple interrupts look like

What is Direct Memory Access

• Used to transfer large blocks of data

• It is a direct transfer to and from memory

• The CPU isn’t actively involved in transfer itself

What are the required conditions for Direct Memory Access

• The I/O interface and memory must be connected

• The I/O controller must be capable of reading and writing to memory

• Conflicts between the CPU and the I/O controller must be avoided

• Interrupt required for completion

What does DMA stand for

Direct Memory Access

DMA Instructions

• Application program requests I/O service from operating system

• To initiate DMA, programmed I/O is used to send information

• Interrupt to the CPU upon completion of DMA

What is the following information that the programed I/O is used to send to initiate DMA

• Location of data on I/O device

• Starting location in memory

• Size of the block

• Direction to transfer: read or write

What are I/O controller functions

• Recognizes messages from device(s) addressed to it and accepts commands from the CPU

• Provides a buffer where the data from memory can be held until it can be transferred to the device

• Provides the necessary registers and controls to perform a direct memory transfer

• Physically controls the device

• Copies data from its buffer to the device/from the CPU to its buffer

• Communicates with CPU

Interconnects Example

What are peripherals

• Devices that are separate from the basic computer

  • Not the CPU, memory, or power source

What are peripherals classified as

Input, Output, and Storage

How do peripherals connect

Ports and Interface to system bus

What are different types of secondary storage

• Online storage

• Offline storage - loaded when needed

• Network file storage

  • File servers, web servers, and database servers

What is flash memory

It is a solid state drive

With large capacity flash memory units

What does flash memory replace as long-term storage

Magnetic dish drives

Is flash memory immune to physical shocks

True

Does flash memory produces lots of heat and noise

False

It generates little heat or noise

How is data read/written in flash memory

It is read/written in blocks

Extra facts on flash memory

• Wear-leveling used to extend life

• Controller logic used to manage memory space and provide fast reads/writes

What are magnetic disks made of

It is a platter made of glass, metal, or plastic with a magnetic coating

How is magnetic polarization determined in magnetic disks

Magnetic polarization is determined by 1s and 0s

Parts of a Magnetic Disk

• Track - Circle

• Cylinder - Same track on all platters

• Block - Small arc of a track

• Sector - Pie-shaped part of a platter

• Head - Reads data off the disk as disk rotates at high speed

What is the high speed the head rotates on a magnetic disk

5400-10000+ RPM

What is the layout of a Hard Disk

What are the different disk layouts

CAV and CLV and Multiple Zone

What does CAV stand for

Constant Angular Velocity

What is CAV

• Number of bits on each track is the same; denser towards the center

• Spins the same speed for every trackc

What does CLV stand for

Constant Linear Velocity

What is CLV

• All tracks have the same physical length and number of bits

• Constant speed reading data off a track

• Drive has to speed up when accessing close to the center of the drive and slow down when accessing towards the edge of the drive

What is Multiple Zone Recording also known as

Zone Bit Recording (ZBR)

Zone-CAV Recording (Z-CAV)

Is multiple zone a compromise between CAV and CLV

True

It is a compromise between CAV and CLV

What is Multiple Zone

• Disk divided into zones

• Cylinders in different zones have a different number of sectors

• Number of sectors in a particular zone is constant

• Data is buffered so the data rate to the I/O interface is constant

Multiple-Zone disk configuration

What is Seek Time

Time required to move from one track to another

What is Latency

The time required for disk to rotate to beginning of correct sector

What is Transfer Time

Time required to transfer a block of data to the disk controller buffer

What is average seek time

Average time to move from one track to another

What is average latency time

Average time to rotate to the beginning of the sector

What is the formula to find the average latency time

½ * 1/rotational speed

What is the formula to find the average transfer time

1/(# of sectors * rotational speed)

What is the formula to find the total time to access a disk block

Average seek time + average latency time + average transfer time

What are the components in a data block format in relation to magnetic disks

• Interblock gap

• Header

• Data

What is a formatting disk

• Establishes the track positions, blocks, and headers needed before use of the disk

What does a disk block format look like

What is a disk array

Grouping of multiple disks together

What does RAID stand for

RAID → Redundant Array of Independent/Inexpensive Disks

What are the different types of RAID Arrays

• Mirrored array

• Striped array

• RAID 0 to RAID 5

What is a mirrored RAID array

• Two or more disks contain the exact same stores of data

How does a mirrored RAID array read data

Alternate blocks of data are read from hard drives and combined

Is access time reduced in a mirrored RAID array

True

Access time is reduced by approximately a factor equal to the number of disk drives in an array

How does read failure work in a mirrored RAID array

Block is marked and then read from the mirrored drive

Extra fact about mirrored RAID arrays

When using three or more mirrored drives, majority logic is used in the event of a failure.

Fault-tolerant computers use this technique

What is a striped RAID array

A file segment is stored divided into blocks on different disks

What is the minimum amount of drives needed in a striped RAID Array

3

Minimum of three drives needed for true stripping because one drive worth of space is reserved for error checking

Is one drive reserved for error checking in a striped RAID array

True

One drive is reserved for error checking

How does Writes work in a striped RAID array

Writes - block of parity words from each block of data is created and put on the reserved error checking disk

How does Reads work in a striped RAID array

Reads - parity data is used to check original data

What are the different RAID levels

RAID 0

RAID 1

RAID 2, 3, 4

RAID 6

RAID 10

What is RAID 0

No error checking or redundancy, but data is placed across all drives for increased speed

What is RAID 1

Mirrored array

What is RAID 2, 3, 4

Arrays that are striped in different ways (deprecated)

What is RAID 5

Error checking blocks are spread across all drives

What is RAID 6

Double parity blocks, two drives per array can fail

What is RAID 10

Mix of performance of 0 with redundancy of 1 used instead of 5 or 6 if performance is important

What is optical storage

Reflected light off a mirrored or pitted surface

What is CD-ROM

• 650 MB of data, approximately 550 MB after formatting and error checking

• Spiral 3 miles long, containing 15 billion bits

• CLV - all blocks are same physical length

• Block - 2352 bytes

  • 2k of data (2048)

  • 16 bytes for header (12 start, 4 id)

  • 288 bytes for advanced error control

Different types of optical storage

Laser strikes land

Laser strikes a pit

What is laser strikes land

Light is reflected into a detector

What is laser strikes a pit

Light is scattered

CD Layout

Standard Disk Layout

What are the different types of optical storage

Medium-powered laser blister technology

What is medium-powered laser blister technology also used for

• CD-R, DVD-R, DVD-R, DVD+R

• CD-RW, DVD-RW, DVD+RW, DVD-RAM

Are there file compatibility issues between the different formats

True