Device management in os – Techniques for device management

Device management in OS greatest challenge. The OS must control a collection of devices with multidimensional differences. Wide ranges are found in device speed, information volume, and communication protocol. OS manage I/O device (e.g) N /w card, mouse, keyboard, HDD Etc.

Device management in OS

Device management in os

Example:  How a device or resource can be allocated to an application program by the OS. If an application process during its execution required a device to perform specific tasks.

The device controller used in the device management operation usually includes three different registers. 

1 command register: The command register is used to contain the information regarding the request issued by an application program. Device controller that specious the type of service request by the application program.

2 Status register: The status register is used to keep track of the status of the device .it contains information about whether or not the device is free to service the rewash of an application program.

3 Date register: The date register holds the necessary data required to be transferring b/w the application program and the corresponding device.

Techniques for Device management    

All the I/O devices can be classified into any one of the following three categories.

1. Dedicated device 

A dedicated device is allocated to a single job. Dedicated devices are devices that are assigned to only 1 job at a time and serve the job for the entire time it is active.

EX- Tape driver, plotter

2. Shared Device

The devices like disks, drums, and other direct access devices are shared devices because these devices can be shared by several jobs at a time. These devices are efficient but difficult to manage.

3. Virtual Device 

Virtual devices are a combination of dedicated devices that have been transformed into shared devices. Some devices can be converted from dedicated devices to shared devices like card readers.

For Example, Printers are converted into shareable devices through a spooling program. That reroutes all print request to a disk.

Device characteristics –H \W consideration

2 storage device- A storage device is a mechanism by which the computer may store information in such a way that this information may be retrieved at a later time. There are three types of storage devices.

1. Serial Access: Where Tij has a large variance (e.g. Tape)

2. Completely direct access: Where Tij is constant (e.g. Tape) semiconductor memory, magnetic core memory.

3. Direct Access: Where Tij has only a small variance (e.g. Drum, HDD)

1. Serial Access Storage Devices (SASD):

An SASD can be characterized as one that relies on strictly physical sequential positioning and accessing of information.

A Magnetic Tape Unit (MTU) is the most common example of SASD.

Example: Audiotape, tape cassette, music or voice, binary information is stored.

2. Completely Direct Access Storage Devices: This device is one in which the access time Tij is a constant. Magnetic core memory, semiconductor memory, are all example of completely DAM.

3. Direct Access Storage Devices (DASD): This device is one that is characterized by small variances. In the access time Tij this has been called DASD

The examples of DASD are as follows:

1. Fixed-Head Drums and disks.

2. Moving-Head Disk and drums. 

Secondary storage stricture

Secondary memory is required in computers to store data instruction for a long period of time is called SS.

• Secondary storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. 

• SSD are those devices whose memory is nonvolatile, means, the stored data will be the system is torched off. 

• The speed of the secondary storage is also less the primary storage.

• There are two types of secondary storage memories. 

1.  magnetic disk 

2.   magnetic tapes.     

1-    Magnetic disks:

 The magnetic disk includes a hard disk and a floppy disk. The working principle is the same for both hard disks and floppy disks.

The magnetic disk contains several platters each platter is divided into circular-shaped tracks and each track is divided into sectors.

2. Magnetic Tape: 

Magnetic tape is a Sequential Access Memory/ device. (ex- Audio caste )  It is a simple but slow technique. Sequential Access Memory to data file means that the computer system reads or writes information to the file sequentially. Slow data transfer speed compared to DMA

Direct Access Memory (DAM)  Data present at any memory location can be accessed directly. The faster way to retrieve data transfer is very fast.  DAM is expensive compare to SAM The terms direct access and random access describe the same concept. They mean that an element of data or instructions (such as a byte or word) can be directly stored and retrieved by selecting and using any of the locations on the storage media.

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