Here you will learn about computer hardware and troubleshooting plus some basic formulas of Microsoft Excel.
BIOS Conventional Memory Software Troubleshooting
PC Hardware
| ||
· Hardware Troubleshooting
Microsoft Excel
| ||
· SUM
|
· COUNT
|
· IF
|
· NESTED IF
|
· COUNTIF
|
· SUMIF
|
· RIGHT
|
· LEFT
|
· FIND
|
· SUBSTITUTE
|
· NETWORKDAYS
|
·
|
PC Architecture and Trouble Shooting
|
CPU:
It controls and directs all the activities of the computer using both internal and external buses. It carries out instruction of a computer program.
CPUs are generally square in shape with transistors arranged in Pin Grid Array( PGA). Prior to 1981, chips were found with two rows of 20 pins known as Dual Inline Package (DIP)
The frequency with which a processor executes instructions is called its clock speed. This is measured in Hertz(Hz).
The storage area for frequently used data and instructions is called internal cache memory.
The supporting circuitry on which a processor’s ability to communicate lies is called the BUS.
BIOS:
It stands for Basic Input Output System. It is build in a PC and is the first code run by PC. It communicates between computer and devices. It is usually stored in ROM. When the operating system needs to access hardware, it would ask the BIOS. The advantage of use of BIOS is it prevents programs to fight over hardware.
Conventional Memory:
It is a read-write memory usable by the operating system and application programs. Besides DOS itself and drivers, there are often programs that are loaded into conventional memory and then keep a portion of them-selves there after they have been terminated. This behavior can be pretty handy as programs like email software can be called up more quickly when parts of them are still located in memory. These programs are called Terminate and Stay Resident (TSR) programs.
Antivirus programs, disk caching programs and network protocol stacks are examples of TSR programs.
Troubleshooting:
Few things to narrow the problem down are
- In DOS/Windows computers, boot the computer “clean”. Booting it “clean” means starting the computer with no software drivers loading. The only things that should be in the AUTOEXEC.BAT or CONFIG.SYS are necessary memory managers and settings to get the computer up and running. Leave out sound card, CD-ROM, network and other devices drivers. You can also book “clean” by using a bootable floppy disk. If the computer functions normally, then the problem is usually software-related, although it could be hardware related and device driver just enabled the device causing the conflict to show itself.
Operating System Error Messages. Every operating system has built in error detection routines. These routines are designed to intercept problems and notify the user. If there is a major problem, these routines will display an error message for the software or hardware component that caused the problem. For example when you try to print to a printer connected to your primary parallel port and the system returns an error like “Error writing to device LPT1” that is more than likely a hardware related problem because a hardware device was mentioned in the error message.- Uninstall and then reinstall the application that’s having problems. This assures that you have the correct version of all the application’s components and that there are no missing files that may be required by the application.
- Look for ways to repeat the problems. Find a way to repeat the problem or look for some type of pattern to the problem.
- Make sure you are using the latest patches. This is especially important with machines that are on network.
- Check the internet.
- Compare and isolate. It can be difficult to determine if an application problem is caused by the software or hardware. The best troubleshooting tools in this case are the twins comparison and isolation. Try comparing how the application behaves on the problem machine and on a machine that you know is working fine, then remove and/ or replace hardware components from two machines to eliminate possible causes and isolate solution.
Hardware Troubleshooting
The first item we are going to discuss is not really a hardware problem, but a hardware troubleshooting aid. Every computer has a diagnostic program built into its BIOS called the Power on Self Test or POST. When you turn on computer, it executes this set of diagnostics. These tests go by pretty quickly so are discussed here.
- The processor is tested. POST runs checks on the CPU. If the tests fail, the system stops with no error message.
- The ROMs are checked. POST computes a checksum for the BIOS ROMs. If the checksums do not match, the system halts with no error message.
- The DMA controller is tested. Again if there are problems, the system halts.
- The Interrupt controller is checked. If there is a problem with this component, the system will give a long beep, then a short beep, then the system will stop.
- The system timing chip is tested. This is not the chip that tells time, but rather the chip that provides timing signals for the bus and processor. If this chip fails, the system will give a long beep, then a short beep, and then halt.
- The BASIC ROMs are tested. Most computers since the IBM AT have not included BASIC, so this step is usually not part of their POST routines. However, on older computers, if the ROMs fail the POST test, it does another long beep, then a short beep and then halts.
- The video card is checked. At this point the system runs the diagnostics for the video card. If it fails, the system issues one long beep and two short beeps and halts. If successful, the video ROM BIOS is copied into RAM and you will usually see a message about the type of video card that the computer is using.
- Expansion boards are initialized. During this part of the POST routine, any expansion boards that need to can initialize and copy their ROMs into upper memory, if necessary.
- RAM is counted and tested. The system tests and counts all RAM that’s installed in the machines by writing a bit to each bit or memory. If a 1 is written and read back successfully, the counter increments. A failure during this portion of POST will generate a “201 memory error” message on the screen.
- The keyboard is tested. The keyboard controller is contacted and signals are sent to detect the presence of a keyboard. Checks for stuck keys are also made. If this test fails a “301 keyboard failure” error message is generated, along with a short beep.
- The cassette interface is checked. Another POST routine only valid on IBM PCs and XTs. If the cassette interface doesn’t work a “131 cassette interface” error is generated.
- Test floppy drives. The floppy disk adapter is contacted and asked to activate the drive motors of any floppy disks, in order. If there are problems, a “601 floppy disk” error is generated.
- Check resources and boot the computer. The POST routine queries any remaining devices (LPT ports, serial ports etc), makes a short beep and then queries the disk drives looking for an operating system. If one is found on either floppy drive or hard disk, it is loaded and the computer is functional. If an operating system can’t be found, most systems will issue an “Operating system not found” error.
Beep Code
|
Problem
|
No Beep, system dead
|
Power supply bad, system not plugged in or power not turned on
|
Continuous Beep
|
Power supply bad, not plugged into motherboard correctly or keyboard stuck
|
Repeating Short Beep
|
Power supply may be dead
|
1 short beep, nothing on screen
|
Video card failure
|
1 short beep, video present but system won’t boot
|
Bad floppy drive, cable or controller
|
2 short beeps
|
Configuration error
|
1 long, 1 short
|
System board bad
|
1 long, 2 short
|
Video card failure
|
Microsoft Excel
|
This section explains some basic functions of Microsoft Excel
Microsoft excel sheet consists of columns and rows. In the fig shown, A,B,C,D… are columns and 1,2,3… are rows. In other words say that verticals are columns and horizontals are rows.
The space occupied by intersection of a column and a row is called a cell. Each cell is given a name as A1, A2,A3..B1 . The cell A1 shows first row of column A, similarly cell C5 will show fifth row of column C.
Here we will learn about some basic formulas. Remember that to type any formula, you will first have to type ‘=’ (equal sign) before the formula.
SUM:
Sum of cells can be calculated as follow
Now we have typed 5 numbers in column A and we want Microsoft excel to find out their sum. And suppose we want to appear the sum in cell A6. Now move to A6 and type there the sum forumula
=sum(A1:A5)
It will calculate the sum of all the numbers in the range A1 to A5.
Now suppose you want to find the sum of values placed at different cells that is at A1,B3,C2 and D2. And we want the sum to appear at D5. Now move to D5 and type
=sum(A1,B3,C2,D2)
A
|
B
|
C
|
D
| |
1
|
6
| |||
2
|
5
|
9
| ||
3
|
5
| |||
4
| ||||
5
|
25
|
COUNT:
This formula counts the number of values in a given range of cells. This formula does not count the blanks. Also remember that this formula only counts the numbers, not the characters
Suppose some values are typed in colums A1,A2,A3 and A5. The count formula typed in cell A6 will be
=count(A1:A5)
A
|
B
|
C
|
D
| |
1
|
2
| |||
2
|
a
| |||
3
|
1
| |||
4
| ||||
5
|
5
| |||
6
|
3
|
As you see the answer is 3, because one cell is blank and one cell contains character value ‘a’. Only three cells contain numbersYou can also use following count formulas
=countblank(A1:A5)
|
It will calculate only blank cells. The result will be 1
|
=countA(A1:A5)
|
It will calculate all non empty cells including numbers and characters. The result is 4
|
IF:
This formula applies condition on a certain values. Suppose some values are typed in a given range A1 to A7. We want Microsoft Excel to tell us which value is greater than 10 and which is less than 10. To know this we type the if formula next to every value in column B. the formula for value in cell A1 will be
=if(A1>10,”Greater than 10,”Less than 10”)
Note that this formula contains three parts separated by commas. The first part is condition which asks the compiler to check values which are greater than 10, the second part shows if value is true, and last part shows if value is false. This mean if the value is greater than 10 then the message “Greater than 10” will appear otherwise the message “Less than 10” will appear
Similarly this formula will be typed for A2,A3 and so on
Nested IF:
In this formula IF condition is nested in another IF condition. Suppose we are given marks of students in a given subject. We wish to mark grade “A” if marks are 90 or greater than it, “B’ if marks are greater than 80, else display “C” for marks lower than 80
Formula will be
=IF(A2>=90,"A",IF(A2>=80,"B","C"))
Note that in the third part of IF condition that is used for value if false, another IF condition is applied.
See another example
COUNTIF:
COUNTIF counts the number of cells that meet criteria specified. Suppose we want to count the number of cells only where a value ‘10’ appears in the given sheet ranging from A1 to A10. The formula will be
=countif(A1:A10,10) countif(range,criteria)
SUMIF:
This formula calculates the sum of a range meeting some specified criteria.
Syntax: SUMIF(range, criteria, sum-range)
Suppose we are given a date as under
We have some types of tools placed in different rooms. Now we want to find total bolts placed in different rooms. In other words we want the sum from column B, where value in column A is “Bolt”.
Sumif(range in column A where some criteria is required, criteria, sum from column B)
=SUMIF(A2:A6,"Bolts",B2:B6)
RIGHT:
This formula returns the last characters of a string based on a number. For example we want to know what are last four characters in a string “My Computer” the answer will be “uter”
Syntax: RIGHT(cell that contains a string, number of characters)
Consider the following example
LEFT:
This formula returns the starting characters of a string based on a number.
Syntax: LEFT(cell that contains a string, number of characters)
FIND:
This formula locates a text string within a second text string, starting from a specified location.
Syntax:
FIND(text which to be find, string in which a text is to find, starting number)
The last argument is optional. If you do not use it, the find function will start from first location.
Consider the example below.
SUBSTITUTE:
This formula substitute new text for old text specified at a given place.
=SUBSTITUTE(cell that contains a text, old text, new text, occurrence of old text we want to replace with new text)
Consider the following example to understand the use of this formula
NETWORKDAYS
Find the whole working days between start date and end date excluding Saturdays and Sundays and any other holiday you mention.
=NETWORKDAYS(start date, end date, holidays)
Example:
See the example below. Note that dates should not be in text format otherwise formula will not work.
Very nice information, thanks for sharing.
ReplyDelete