Complete Study On I/O Devices Hardware And Their Implementation

1. SARVAJANIK COLLEGE OF ENGINEERING AND TECHNOLOGY
COMPUTER ENGINEERING DEPARTMENT
B. E.-II, CO-E, SEM-IV
(EVEN-2019)
ALA Presentation
on
“INPUT OUTPUT MANAGEMENT”
Subject Name : Operating System (2140702)
Prepared and Presented by (Group No. : 12)
Uttam Thummar (170420107559)
Dhriti Uttamchandani (170420107560)
Keyur Vadodariya (170420107561)
Aditya Vaghela (170420107562)
Sanket Variya (170424107563)
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2.  Principle of I/O hardware:
 I/O devices
 Types of I/O device
 Device controllers
 Direct memory access(DMA)
 Direct memory access controller
Content2

3.  I/O devices are the pieces of hardware used by a human (or
other system) to communicate with a computer. For instance,
a keyboard or computer mouse is an input device for a
computer, while monitors and printers are output devices.
I/O devices3

4.  I/O device are divided into two categories:
I/O devices(Cont…)
I/O device
Block device
Character
device
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5.  A block device is one that stores information in fixed-size
blocks, each one with its own address.
 Common block size range from 512 bytes to 32,768
bytes.
 All transfers are in units of one or more entire blocks.
 Possible to read or write each block independently of ail
the other ones.
 Examples :- hard disks, CD-ROMs, USB etc…
Block device5

6.  A character device delivers or accepts a stream of
characters, without regard to any block structure.
 It is not addressable and does not have any seek
operation.
 Printers, network interfaces, mice(for pointing), rats(for
psychology lab experiments), and most other devices
that are not disk-like can be seen as character devices.
 Example : serial ports, parallel ports, sounds cards etc…
Character device6

7. Difference between block and
character devices
7
Block Character
Block Device are hardware devices
which randomly access fixed-sized
chunks of data.
Character devices are accessed as a
stream of sequential data, one byte
after another.
Seeking is possible. Seeking is not allowed.
Reads and write done by buffer cache
mechanism by bread(), bwrite().These
request may be asynchronous
The read() and write() calls do not
return until the operation is complete.
More complex than character driver. Less complex than block driver.
The kernel does have to provide an
entire subsystem to block device.
The kernel doesn’t have to provide an
entire subsystem to the character
device.
Eg: Hard disk, Pen drive Eg: Keyboard device, serial port.

8.  I/O units typically consist of a mechanical component and
an electronic component.
 The Device Controller works like an interface between a
device and a device driver. I/O units (Keyboard, mouse,
printer, etc.) typically consist of a mechanical component
and an electronic component where electronic component
is called the device controller.
Device controller8

9. Device controller(Cont…)
 Any device connected to the computer is connected by a
plug and socket, and the socket is connected to a device
controller.
 Following is a model for connecting the CPU, memory,
controllers, and I/O devices where CPU and device
controllers all use a common bus for communication.
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10. Device controller(Cont…)
 Graphically representation of device controller
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11.  Slow devices like keyboards will generate an interrupt to
the main CPU after each byte is transferred. If a fast
device such as a disk generated an interrupt for each
byte, the operating system would spend most of its time
handling these interrupts.
 So a typical computer uses direct memory access
(DMA) hardware to reduce this overhead.
Direct memory access11

12.  Direct Memory Access (DMA) means CPU grants I/O
module authority to read from or write to memory without
involvement.
 DMA module itself controls exchange of data between
main memory and the I/O device.
 CPU is only involved at the beginning and end of the
transfer and interrupted only after entire block has been
transferred.
Direct memory access(Cont…)12

13. Direct memory access controller
 Direct Memory Access needs a special hardware called
DMA controller (DMAC) that manages the data
transfers and arbitrates access to the system bus. The
controllers are programmed with source and destination
pointers (where to read/write the data), counters to track
the number of transferred bytes, and settings, which
includes I/O and memory types, interrupts and states for
the CPU cycles.
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14. Configurations of DMA
 Two Configuration For DMA Transfer:-
1. Single Bus
2. I/O Bus
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15. Direct memory access controller (Single Bus)15

16. Direct memory access controller (I/O Bus)16
1. Device driver is told to
transfer disk data to
buffer at address X.
2. Device driver tells Disk
Controller to transfer C
bytes from disk to buffer
at address X.
3. Disk Controller Initiates
DMA Transfer
4. Disk Controller sends
each byte to DMA
controller.
5. DMA controller transfers
bytes to buffer, increases
the memory address,
decreases the counter C
until C becomes zero.
6. When C becomes zero,
DMA interrupts CPU to
signal transfer completion.

17. DMA Modes Of Operations
1. Word-at-a-Time Mode
 In this mode, the DMA controller requests the transfer of one word
and gets it.
 If the CPU also wants the bus, it has to wait.
 The mechanism is also called “cycle stealing” because the device
controller sneaks in and steals an occasional bus cycle from the CPU
once in a while, delaying it slightly.
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18. DMA Modes Of Operations
2. Block Transfer Mode
 In block transfer mode the DMA is programmed to transfer a block
and does not pause or halt until the whole block is transferred
irrespective of the requests received meanwhile.
 The DMA retains control of the memory bus for the duration of the
memory transfer.
 The negative aspect of operating in this mode is that the CPU will
not be able to access the memory bus until the DMA controller
completes the memory transfer.
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19. DMA Modes Of Operations
3. Transparent Mode
 In transparent mode, the DMA controller transfers data only when
the CPU is performing operations that do not use the system buses.
 The primary advantage of transparent mode is that the CPU never
stops executing its programs and the DMA transfer is free in terms
of time, while the disadvantage is that the hardware needs to
determine when the CPU is not using the system buses, which can
be complex.
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20. Advantages & Disadvantages Of DMA
Advantages :-
 DMA allows a peripheral device to read from/write to memory without
going through the CPU.
 DMA allows for faster processing since the processor can be working
on something else while the peripheral can be populating memory.
Disadvantages :-
 requires a DMA controller to carry out the operation, which increases
the cost of the system.
 Cache Coherency.
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21.  Modern Operating Systems (Third Edition) by Andrew S
Tanenbaum, Prentice Hall India (2008).
 Operating System Concepts (8th Edition)by Silberschatz,
Peter B. Galvin and Greg Gagne, Wiley-Indian Edition
(2010).
 www.slideshare.net
References21

22. Thank You…22