Difference between Static RAM (SRAM) and Dynamic RAM (DRAM)

     SRAM  VS DRAM

                    

Types Of RAM

RAM is the main memory of the computer. It holds the data unit the system is turned off. Once the system is switched off, the data is lost.As a result, it is known as the temporary data storage area. There are two types of RAM, Static RAM and Dynamic RAM. 

Static Random Access Memory(SRAM)

SRAM is the type of semiconductor memory. It stores the data as long as the power is supplied to the system . Once the power is turned off or is lost temporarily,data stored in SRAM is lost. SRAM uses six transistors for each memory cell. Due to more number of transistors present in the cell, the cell do not refresh frequently.Hence,the data is stored for longer period. Refreshing a cell means re-writing data in a cell.

SRAM is faster in accessing data. The data accessing speed of SRAM makes it behave like a cache memory .SRAM is expensive as compared to DRAM . Example of SRAM is all types of Cache Memory.

Dynamic Random Access Memory(DRAM)

The lifetime of data in RAM is very short.It is approximately for four milliseconds.The data in DRAM are stored in memory cells. Each memory cell contains a pair of a transistor and a capacitor.Each memory cell contains a pair of a transistor and a capacitor.Each memory cell is referred as a bit of data, the smallest amount of information that the system can work with. The memory cells of DRAM are refreshed by DRAM controller after every few milliseconds to retain the data in the memory.
The cells in DRAM are arranged in rows and columns .Each  cell has a row and a column reference number. DRAM accesses the data using the cell reference number. DRAM is less expensive than SRAM

Types of RAM

Upgrading The Memory

The memory of the system must be upgraded to increase the speed of the system.The memory is upgraded either by changing the previous RAM or by adding one more RAM with the previous RAM. The installation of a new RAM depends on the number of the free memory slots available on the motherboard.

Before installing a new RAM,check the type of RAM for mounting on the motherboard. The new RAM should match with the configuration of the previous RAM and should supported by motherboard and processor.

To upgrade the memory of the system we have to take following steps:

• Shutdown the computer and disconnect the power cable from SMPS and all the peripheral devices attached to it.
• Remove the system case.
• Wear an anti-static wristband or any other static control device before touching any of the computer components.
• Hold the RAM module by its edges.Do not touch the chips and connectors of the RAM module.
• Hold the RAM module perpendicular to the memory socket.
• Check the notches of the RAM module before placing it on the memory socket.
• Put a slight pressure while inserting the RAM module on the memory socket.
• Put the case back to the computer.
• Connect all the peripheral devices to the computer.
• Switch on the computer and check the current amount of the RAM.

Troubleshooting of Motherboards

If your system Crashes repeatedly,it is possibly due to motherboard failure. However , actual motherboard failure is very rare. It is possible that some other problems like a loose connection, power failure or overheating may cause system failure.

We have to take the following steps :

• Turn off the system and remove the power cord from the power supply.
• Check connections on the Motherboard .
• Restore the BIOS settings to default setting .
• Ensure that the motherboard is not touching the system case.

Precautions:

• Wear an anti static wristband.
• Cleaner 

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COMS battery checking

Actually CMOS is not a battery ,it is a technology which is used to construct Integrated Circuit. CMOS stands for Complementary Metal Oxide Semiconductor. This technology is basically used in microprocessor, micro-controller,RAM ,different logic circuit.
To check the CMOS battery we have to take following steps:

1. Remove the CMOS battery from the motherboard.
2. Set the multimeter in DC voltage mode
3. Put the red probe on +ve side (mentioned on the CMOS battery) and black probe on opposite side of the CMOS battery.
4. If the output voltage shown is grater than 2.5 volts on  multimeter then it is OK otherwise replace the battery.

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Starting a PC for the First Time

When we start the PC,the Basic Input Output System(BIOS) runs a test to check if all the peripheral devices ,memory and hardware of the PC will are working properly.This test is called the Power on Self Test (POST). The PC will boot only if the results of the test are positive.POST is performed before the PC actually boots the operating system.

If any the hardware components of the PC are not in proper condition, the PC will generate beeps.In some cases,if the problem is serious,the PC will not boot at all. The POST happens before most of the components of the PC start.

The following are the functions performed by POST:

• Checking the power supply
• Checking the motherboard
• Comparing the system configuration with the PC configuration program to find any changes made
• Checking the memory devices and drives
• Checking the System memory
• Starts the display and audio devices

The error that causes the system to stop booting are of two types-Non-Fatal and fatal. In case of non-fatal errors like problems in the extended memory,an error message usually appears on the screen.They allow the computer to continue the boot process. In-case of fatal errors like problems in the processor,the boot process stops immediately and the user gets a series of audible beeps. In-case there are no errors in the system configuration or devices,a single beep follows the POST . Then the booting process of the PC starts and the operating system is loaded.

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All the User account (including Administrator) are disable

First you have to enable administrator account. To do that the several steps have to be taken-

1. Restart your System and hit several time F8 key.
2. Chose "Safe mode with command prompt."
3. In command prompt  type 

          "net user administrator /active:yes"

    4. Protect your administrator with password.

Create System Image and System Repair Disc

• Run this task by Administrative Rights

Hardware/Software Requirements:

• External Hard disk/ Blank DVD Disk

To Create System Image and System Repair Disc

1. Click Start→Control Panel→System and Security→Backup and Restore
2. Click on Create a system image 

          select your option among the three options

          a. On a hard disk

          b. On one or more DVDs

          c. On a network location   

     3. Select the disk where you want to save the backup and click Next button.

     4. Click Next Button.

     5. Click on Start backup button. Create a system Image screen appear.

     6. Create a system repair disc screen appear.

     7. Click on Yes button and Insert a blank writable DVD in DVD-ROM Drive.

     8. Click Create Disc.

     9. The creating a System Repair  Disk dialog box appears.

    10. Using the system repair disc screen appears.

    11. Click Close.

OSI Layer and their functions

   LAYERS                     FUNCTIONS                        DATA FORMAT             DEVICE USED

7 Application           Creating a data at user interface             File                             Computer

6 Presentation          Compressing ,Encryption                       File                            Computer

5 Session               i. Establish connection between
                                  transmitter and receiver .                       N.A                            Computer
                             ii. Maintaining, controlling, terminating
                                  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.
                 

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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

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Motherboard Checking..

To check motherboard we have to take following steps:

1. Check motherboard for cracks on account of overheating of equipment.
2. Physically observe any scratches or discontinuity in PCB(Printed Circuit Board) path.
3. Check for burnt ICs or component.
4. Check the VGA connector for dry soldering or loose connection or replace the connector.
5. Check North Bridge and South Bridge ICs physically for loose connection or dry soldering.
6. Check north and south bridge IC whether they are getting heated by putting your index finger on them.
7. Check the processor whether it is gradually heating up or not by putting your index finger on top of the processor.
8. If the processor is cool then check the voltage regulator ICs whether short or open or measuring  voltage across the leads using multimeter in diode mode.
9. Update BIOS from motherboard driver CD or you can download from the Internet.
10. Replace BIOS and check.
11. Use the debugging card to know the source of the problem.