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NETWORK BASICS

Network A system of interconnected computers and computerized peripherals such as printers is called computer network. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by either wired or wireless media. A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other.  


Network application
A Network application is any application running on one host and provides a communication to another application running on a different host, the application may use an existing application layer protocols such as: HTTP(e.g. the Browser and web server), SMTP(e.g. the email-client). And may be the application does not use any existing protocols and depends on the socket programming to communicate to another application. So the web application is a type of the network applications. 
There are lots of advantages from build up a network, but the th…

BIOS & CMOS

Methods to Accessing BIOS or CMOS setupBIOS (basic input/output system) is the program a personal computer's microprocessor uses to get integral part of your computer and comes with it when you bring it home. (In contrast, the operating system can either be pre-installed by the computer system started after you turn it on. It also manages data flow between the computer's operating system and attached devices such as the hard disk, video adapter, keyboard, mouse and printer. BIOS is a manufacturer or vendor or installed programmable read-only memory (EPROM) chip. When you turn on your computer, the microprocessor passes control to the BIOS program, which is always located at the same place on EPROM. By the user.) BIOS is a program that is made accessible to the microprocessor on an erasable  

When BIOS boots up (starts up) your computer, it first determines whether all of the attachments are in place and operational and then it loads the operating system (or key parts of it) into your computer's random access memory (RAM) from your hard disk or diskette drive. With BIOS, your operating system and its applications are freed from having to understand exact details (such as hardware addresses) about the attached input/output devices. When device details change, only the BIOS program needs to be changed. Sometimes this change can be made during your system setup. In any case, neither your operating system nor any applications you use need to be changed. Although BIOS is theoretically always the intermediary between the microprocessor and I/O device control information and data flow, in some cases, BIOS can arrange for data to flow directly to memory from devices (such as video cards) that require faster data flow to be effective. 

BIOS Driver

The BIOS's first task is to configure all the system hardware with basic drivers so the system can get up and running. These drivers will set up and prepare the system memory and configure any peripheral devices for use such as the hard drives, optical drives, and video card. The BIOS loads a basic system that's able to read the devices that contain the system operating system. 

BIOS BOOT

The BIOS typically displays a splash screen when loading the initial CMOS settings and the hardware drivers. BIOS initiates the operating system boot process after all the drivers are loaded and configured. The operating system contains more robust versions of the system drivers and replaces them with the BIOS versions once they're loaded. The BIOS boot process is like the ignition on a car, it gets the system ready for use. 

BIOS performance

The BIOS in a PC can affect the system's performance in two ways. 
  • The efficiency of the BIOS code. 
  • The control it affords over the system resources. 
 Most of the programs do not know the contents of the BIOS routines and hence the assembly language instructions of each BIOS routine can vary considerably among different BIOS. The most efficient BIOS routine will be the one with the least number of instructions. The program will hence require to execute fewer steps using fewer clock cycles every time it calls a BIOS routine. As a result the system runs faster. This is however only possible when a program takes advantage of BIOS routines and does not side step the BIOS to take direct hardware control. A more important performance difference depends on upon how a BIOS initiates its host computer. Some BIOSs do a better job in optimizing the relationship between the Microprocessors local bus and the IO channel. A better BIOS automatically checks for the best operation of all available features. Through advanced setup procedures, it may also give the user manual control of these vital system parameters so that you can improve its settings. 

ROM BASIC: One section of the BIOS code is usually not duplicated by computer makers since it is not only copyrighted but also undocumented as to function and entry points. This section is actually a primitive programming language called “Cassette BASIC” or sometimes called as ROM BASIC. The original purpose of the cassette BASIC language was to enable the first IBM computer to do anything without the need for a disk drive. When you first boot your computer without a system disk, any software which is supposed to execute will have to load from some disk will fail and you usually get an error “non-system disk / error”. But even to run this check program, IBM computers have to start the cassette BASIC language executing. All advanced versions of BASIC are designed to augment this cassette BASIC already in the computer's ROM.  

ROM TYPES 

There are various types of ROM. Let’s have a look on this segment. 

Each type has unique characteristics, but all types of ROM memory have two things in common: 

➣Data stored in these chips is non-volatile it is not lost when power is removed. 
➣Data stored in these chips is either unchangeable or requires a special operation to change. 

There are four basic ROM types: 

ROM - Read Only Memory  
PROM - Programmable Read Only Memory  
EPROM - Erasable Programmable Read Only Memory  
EEPROM - Electrically Erasable Programmable Read Only Memory 

Now we are going to discuss about various ROM. 

[ROM - Read Only Memory] 

ROM is "built-in" computer memory containing data that normally can only be read, not written to. ROM contains the programming that allows your computer to be "booted up" or regenerated each time you turn it on. 

[PROM - Programmable Read Only Memory] 

Creating ROM chips totally from scratch is time-consuming and very expensive in small quantities. For this reason, developers created a type of ROM known as programmable read-only memory (PROM). Blank PROM chips can be bought inexpensively and coded by the user with a programmer. 

[EPROM - Erasable Programmable Read Only Memory]

Working with ROMs and PROMs can be a wasteful business. Even though they are inexpensive per chip, the cost can add up over time. Erasable programmable read-only memory (EPROM) addresses this issue. EPROM chips can be rewritten many times. Erasing an EPROM requires a special tool that emits a certain frequency of ultraviolet (UV) light. EPROMs are configured using an EPROM programmer that provides voltage at specified levels depending on the type of EPROM used. 

[EEPROM - Electrically Erasable Programmable Read Only Memory] 

EPROMs are a big step up from PROMs in terms of re-usability, they still require dedicated equipment and a labor-intensive process to remove and reinstall them each time a change is necessary. Also, changes cannot be made incrementally to an EPROM; the whole chip must be erased. Electrically erasable programmable read-only memory (EEPROM) chips remove the biggest drawbacks of EPROMs. 

BIOS update:

Computer or motherboard manufacturer periodically updates the BIOS to fix bugs, add compatibility with new devices, improve caching functions, and make several other hardware tweaks that can speed up your boot time and fix annoying issues. These updates are available at the manufacturer's site. Let’s discuss how the BIOS upgrade process is goes. 

Step 1: Identify your current BIOS version.

Check your BIOS version, without restarting your PC, by using msinfo32.exe (as described in the text). 

Step 2: Check your PC/motherboard manufacturer's Website for BIOS updates. 

Most PC manufacturers handle BIOS updates based on your specific line and model, so head over to your manufacturer's support page and check its listings for your PC, because if you download and install a BIOS intended for a different model, your PC probably won't work (although most BIOS updaters are smart enough to notice if you try to install them on the wrong hardware). If there is a BIOS update file available, grab it--along with any documentation it comes with, because often warnings and specific instructions are contained in the Read Me docs.  Those of you who assembled your PC yourself will need to look for BIOS updates from your motherboard manufacturer's Website. If you don't remember your motherboard's model number, you can look it up without opening up the case by downloading and running CPU-  

Step 3: Read the included documentation. 

Your PC's BIOS handles a lots of features. 

Step 4: Update your BIOS. 

Most new PCs have a fairly easy BIOS update procedure: Just download the .exe file from your PC manufacturer's Website, quit all open programs, run the .exe, and let it handle the patch; then reboot. 

BIOS Security

This is the more stable security in computer system which helps our computer prevent from data thefts & also from other’s unauthenticated access. 

Putting Password to BIOS:  

Step 1

To get the BIOS platform on your pc or laptop screen Press the prompted key; often, it's an F-Key, Delete, or ESC. Navigate with the arrow keys, select with Enter, and back out with ESC. 

Step 2

Select the security with the cursor and choose "Set User password “or "Set supervisor Password". 

Once you select the any option in between Set supervisor password or Set user password, it will ask for BIOS password. Put the BIOS password in the box. 

Step 3

Once the password is being given use space bar to save the updated configuration. 

Step 4

After being confirmed pc or laptop will starts automatically. 

Concept of CMOS

BIOS and CMOS work together, but they do different things. The BIOS contains programs that the CPU needs to communicate with the various devices on the motherboard. The BIOS can't be rewritten. It's ROM or Read Only Memory. CMOS on the other hand is RAM or Random Access Memory. The CMOS contains the parameters for programs in BIOS in order to access certain devices.  When we add a new hard drive into the system, it will probably have different parameters than the one that was in our PC before. In that case, we actually update the CMOS, the Random Access Memory chip, with the new parameters for the new hard drive. To change the data stored in CMOS memory we can use a CMOS editor program that is part of our BIOS. When the CPU needs to access our new hard drive, it loads the appropriate programs from the BIOS, and those programs then check the CMOS for parameters of that new hard drive. BIOS and CMOS are sometimes called just the CMOS or just the BIOS. But remember, we can't access the BIOS directly to change anything, we're actually changing parameters in the CMOS. The CMOS also is where our system clock runs. Our operating system pulls time from the CMOS. CMOS chips are usually 64K in size and just like any other Random Access Memory chip, the data in the CMOS is not persistent. Remember that with the BIOS, the read only chip, we're talking about persistent data. If we shut the system off and turn it back on, the content of the BIOS is intact. CMOS on the other hand will lose its contents if it loses power, and because of that the CMOS has to have a constant supply of electrical current to keep its data intact. To do that, we have to use a battery. On older systems it was 5 volts, and on newer systems it's 3.3 volts. This battery keeps the contents of the CMOS chip intact while the system is shut down. The CMOS battery can be a low-voltage dry cell, lithium mounted on the motherboard, or even AA batteries in a housing clipped on a wall inside of the case. 

Newer systems build the battery into the CMOS itself, so we won't find a separate battery in that case. If the voltage of the battery drops significantly, we may lose CMOS settings every time we power-off or power-on our computer. If a CMOS battery fails, replace it and afterwards reenter the CMOS information. During the computer's startup procedure, we can press one or more keys to open a CMOS editor so we can change the data stored in CMOS memory. This CMOS setup program is part of the BIOS program. The key or keys we press to open the CMOS editor depend on the BIOS manufacturer. The easiest way to find out which key to press is to read the screen as it boots or to consult the motherboard documentation. The most common keys are Delete, Insert, F1, and F2. We can edit CMOS settings to change the boot device order, to enable or disable motherboard devices, to add a password to the setup program to prevent unauthorized access, to configure processor or memory settings (such as when you need to set operating speeds or when you want to overclock hardware settings), and to manually configure device properties for legacy devices. If we set a BIOS password and then forget it, we won't be able to edit CMOS settings. To remove the password for most motherboards, move or remove an appropriate jumper, and then replace it after a specific period of time. Removing the battery also works, but that will remove all CMOS data, not just the BIOS password.

POST (Power on self-test)

POST stands for "Power on Self Test." It is a diagnostic program built into the computer's hardware that tests different hardware components before the computer boots up. The POST process is run on both Windows and Macintosh computers. While the exact tests performed may vary between machines, most POST sequences check the vital hardware components, such as the power supply, RAM, and system bus. If any of these tests fail, the POST process will return an error message. This message may be displayed on the screen or may be output in the form of beeps or blinking lights. The most common type of POST error is a memory error. This can be caused by one or more bad memory modules or a memory chip that is loose or not fully seated. If the post process fails on your computer, you may need to check your computer's manual to see what the error code means. If it is a memory error, you may be able to fix the problem by removing, reinstalling, or replacing the bad memory module. If the error is caused by another component, you may need to have your computer serviced by an authorized technician. The POST process runs quickly at the beginning of the boot sequence before the operating system loads. Therefore, you most likely will not notice it unless there is an error. 

If the POST process finishes without encountering any errors, your computer will boot up normally.

Note: Some POST errors are considered "fatal" while others are not. A fatal error means that it will halt the boot process immediately (an example would be if no system memory at all is found). In fact, most POST boot errors are fatal, since the POST is testing vital system components. 

POST card
  
A POST test card is a small diagnostic tool that displays error codes generated during the Power on Self-test. These errors, called POST codes, correspond directly to a test that has failed and can help determine what piece of hardware is causing an issue. Most POST test cards plug directly into expansion slots in the motherboard while a few others connect externally via a parallel or serial port. 

POST error Code

Now we will discuss about various POST card codes which basically helps to find out the errors by POST code. Let’s discuss about it. 

      PCI
POST CODE
       70

Devices
Post Code
     A1
     A2
     A3
     A5




Configuration
Post Code
     C3
     
     C6


Storage Media
Post Code
     D0
     D1
SHORT NAME
PCI Device Disable


Short Name
Keyboard Test
Parallel Port
Serial Port
Mouse





Short Name
Memory Size

HD Detect




Short Name
Floppy Disk
Hard Disk


DESCRIPTION
Disable all the PCI device on PCI bus 0

Description
Check Keyboard Presence
Check Parallel Port Presence
Check Serial Port Presence
Check Mouse Presence

Description
Check the system memory size
Hard Disk detection




Description
Floppy disk test
Hard disk test


System-components
Post Code
     00
Short Name


Post Error
 Description


Generic Post error
     20
    
Refresh Signal

Check if the refresh signal (HW) changes its status property

     21
    
Keyboard Controller

 Test the 8742 keyboard controller
     22   
BIOS Memory

 Performs ROM BIOS memory checksum
     23
Timer channel #2 test 8254 timer Controller, channel #2 (timer #0, counter #2)
     24
DMA Channel #1 Test 8237 DMA controller #1
     25    
DMA Channel #2 Test 8237 DMA controller channel #2
     26 
DMA Page
Test DMA page registers
     27   
INT Controller Ch#1
Test 8259 channel #1 (Master Interrupt Controller)
    28
INT Controller Ch#2
Test 8259 channel #2 (Slave Interrupt Controller)
    29 
Shutdown Byte
Test the shutdown byte in real time clock CMOS memory
    2A
IRQ 0 Line
Test the IRQ 0 signal (HW)
    2B
Co-processor
Test the 80x87 math co-processor device
    2C
RTC
Test the Real Time Clock Device
































System Memory

POST Code



Short Name



Description
40

First 64 Kbytes

Test the first 64Kbytes memory area
42

Base Memory Test

Test the system memory from 64 Kbytes to 640 Kbytes
43

Extended Memory

Test the 2nd the 3rd and the 4th Mbytes of system memory area
44

Protected Mode

Test the protected mode entry

46

Memory Size

Check system memory size

47

Extended Memory

Test the extended memory area

49
L2 Cache Memory
Test the L2 cache memory

BOOT 
Process 

The boot process is something that happens every time you turn your computer on. You don't really see it, because it happens so fast. You press the power button come back a few seconds later and Windows XP, or Windows Vista, or whatever Operating System you use is all loaded.  

1. The first step your computer does when you press the power button, is to turn the Computer Power Supply on. Once a 'Power Good' signal is sent to the motherboard, the CPU then (understanding that the power supply is stable) looks for the ROM bios. 

2. The CPU looks to the ROM bios for the first instruction, and the first instruction is to run the POST (Power-On-Self-Test).  

3. The POST first checks the bios and then tests the CMOS RAM. If there is no problems with this then POST continues to check the CPU, hardware devices such as the Video Card, the secondary storage devices such as the Hard Drive, Floppy Drives, Zip Drive or CD/DVD Drives. 

4. If there are any errors found then an error message is displayed on screen or a number of beeps are heard. These beeps are known as POST beep codes. The reason the computer sometimes uses beep codes instead of displaying an error message is because the video card has not yet been initiated or there may be an error with the card.  

5. Next the bios finds the video card and runs the video card's bios. This usually is the first thing that modern machines display on the screen. After that the computer looks at the other devices and runs their bios' if they have one. 

6. The bios then displays the system configuration. 

7. During the display more tests are conducted including the test that shows your computer testing the memory. If there are any problems found from now on they will be displayed in a text message on the screen. 

8. After that the bios searches for something that it can boot from. This can be set in the CMOS under boot sequence. It can be set to the A: Drive (Floppy) C: (Hard Drive, Primary Partition) D: (CD/DVD Drive) or others such as the USB drive or network card (depending on the bios). 

9. Once the target boot device has been selected the bios will search for the Master Boot Record (MBR). If it is searching for a hard drive it looks at cylinder 0, head 0, and sector 1. 

10. Once a valid volume boot sector is found the bios has done its job and hands over control to the Operating System that completes the booting process. It will also conduct a few hardware tests. 

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