OSI Layer and their function

   LAYERS                     FUNCTIONS                        DATA FORMAT             DEVICE USED

7 Application           Creating a data at user interface             File                             Computer

6 Presentation          Copressing ,encription                           File                            Computer

5 Session               i. Establish connection between
                                transmiter and receiver .                        N.A                          Computer
                             ii. Maintaning, controling,teminating
                                the communication

4 Transport            Identifying the relevant process or we       Segment                  Computer
                              can say: "Process-to-process "delivery.

3 Network             Identify relevant host or we can say         Data gram                 Router
                               "host-to-host" delivery .

2 Data link            Identifying relevant hardware.                   Frame                         Switch

1 Physical             Use for  establishing electrical link            Bits( 0 & 1 )     Hub,Cable,wires
                            between the each pair of devices.
                   

Boot MGR missing

When a message like 'boot mgr missing press Alt+Ctrl+Del to restart'

• First goto BIOS and set CD or DVD drive as first boot priority .
• Now insert microsoft product DVD 'on system repair disk and restart the computer'.
• Click on the repair option .Its starts finding the OS location on the hard disk and after few second the exact drive letter with size will appear.
• You can see that your operating system is there in a drive say(Ex. C:).
• Now you also see in the same box -two options

          a. Repair your computer.

          b. System image.

Select the 1st option .You will now find several options to repair your computer among them choose  'start to repair ' your system automatically start repairing your OS and finally it will produce report.Go through the report and see each testing steps whether it is completed successfully or not.If all steps completed successfully then your system is repaired.
If not then perform next step.
Among those several options as explained command prompt.

           :\>c:

           c:\>dir

           c:\>bootrec fixmbr

           c:\>bootrec fixboot

           c:\>bootrec rebuild bcd

           c:\>exit

•  Restart your computer