1) A device manager, either inside or outside the kernel, coordinates communication between applications, drivers, and devices by managing I/O requests and interrupt queues. 2) The device manager creates a kernel interface and API to control devices by activating their register-specific actions. 3) Device management involves polling, interrupts, and DMA and supports various I/O approaches including programmed, interrupt-driven, and DMA-driven I/O.

1. DEVICE FILE AND INPUT
OUTPUT SUBSYSTEMS
MANAGEMENT
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2.  Device manager ( inside OR outside kernel space ) is
the software that manages these for all.
 The manager co-ordinates B/W application process ,
driver and device- controller.
 The device manager polls the requests at the devices
and the actions occur as per their priorities .
 The device manager manages input & output interrupt
queues .
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3.  The device Manager creates an appropriate kernel
interface & API , and that activate the control register
- specific actions of the device .
 The device controller is activated through the API and
kernel interface . An ‘OS’ device manager provides &
executes the modules for managing the devices & their
driver ISR’s .
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4. 1. If manages the physical as well as virtual devices
like the pipes and sockets through a common
strategy .
2. Device management has 3 standard approaches to
3 types of device drives
 Programmed I/O’s by polling the service need
from each device .
 Interrupt from the device driver ISR and
 DMA operation used by the devices to access the
memory.
3. A device manager has the functions given
i.
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5. FUNCTION OF A DEVICE MANAGER:
FUNCTION ACTION
Device detection & addition
Provides the codes for detect-
ing the presence of various
devices.
Then the adding them for the
use of os device driver.
Device detection Provides the codes for deny-
ing the device resonance.
Resticate device to specific
process
Resticate a device access to
one process only an instant.
Device access
manage
I. Sequential access
II. Random access.1/25/2015 J.SUDARSHANREDDY

6. SET OF COMMAND FUNCTIONS FOR DEVICE:
COMMANDS ACTION
Create & open Creating & configuring &
Initializing the device.
Write Write into the device buffer.
Read Read from the device buffer.
Close & delete Close is for de-registering
the device from the system
& delete is for close &
deleting the device.
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7. FILE SYSTEM ORGANISATION &
IMPLEMENTATION:
1. A file is named entity on a magnetic disk, optical
disk or system memory.
2. A file contains the data, characters & texts.
3. It may also have a mix of each os may have
differing abstracts of a file.
*A file may be a named entity that is a structured
record as on a disk having random access in the
system.
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8. * A file may be a structured record on a RAM analogous
to disk & may also be either separately called RAM disk
or simply a file.
* A file may be an unstructured record of bits or byte’s.
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9. SET OF COMMAND FUNCTIONS IN THE
PORTABLE OS (POSIX) FILE SM:
COMMAND IN POSIX ACTIONS
Open Creating the file
Write Writing the file
Read Reading the file
Close Closing the file
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10. SET OF COMMAND FUNCTIONS IN THE
PORTABLE OS (POSIX) FILE SM:
COMMAND IN POSIX ACTIONS
Open Creating the file
Write Writing the file
Read Reading the file
Close Closing the file
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11. TYPES OF FILE SYSTEM:
1) BLOCK FILE SYSTEM:
 It’s application generates records to be saved
into the memory.
 These are first structured into a suitable format
& then translated into block systems.
1) Byte stream file system:
 It’s application generates record streams.
 These streams are to be saved into the memory.
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12. I/O SUBSYTEMS:
 I/O ports are the OS device management
subsystems.
 Drivers communicate with the many devices that
use them.
 I/O instructions depend on the hardware
platform.
 I/O subsystems differ in different OS’s.
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13. TYPES OF I/O OPERATIONS:
1) Synchronous:
 There are may be saperate functions in RTOS.
In case of traditional OS it is supperate.
 These are at certain fixed data transfer rates.
 A task blocks tills completion of the I/O.
e.g. A write function, write () for 1KB data transfer
to a buffer.
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14. 2) Asynchronous:
 Asynchronous I/O operations are at the variable
data transfer rates.
 If provisions for a process of high priority not
blocked during the I/O’s.
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15. I/O SUBSYSTEM IN A TYPICAL OS:
SUBSYTEM’S HIERARCHY ACTIONS & LAYERS
Application
An application having a
sub layer between the
application & I/O
Functions.
I/O device driver
Functions
These are device
dependent OS
Functions.
A driver may interface
with a set
Of library functions.
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