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| Mastering the Calculator |
Mastering the Scientific Calculator
When you sit down to take an exam at a testing center, the test engine becomes a locked door between you and the operating system. You cannot exit the testing program without quitting the test, or shell out to any other program-with one exception. The Scientific Calculator has been enabled in most of the new exams and you can bring it up at any time without exiting the test.
The reason for its presence requires an historical view of the Microsoft networking products and certifications. With the first versions of Windows NT, the default networking protocol installed was NetBEUI. As the versions incremented, TCP/IP came more to the forefront, but was still just one of several networking protocols. With Windows NT 4.0, TCP/IP was installed by default, but could always be de-selected during the installation. To reflect this, the certification track treated TCP/IP as an elective-not a requirement for certification.
With Windows 2000, you must utilize TCP/IP to be able to take advantage of the features new to the operating system. To reflect this, there is no longer an exam on TCP/IP in the certification track, let alone as an elective. Instead, knowledge about the protocol is required on all the exams. Working with TCP/IP addresses and subnets requires knowing how to work with binary numbers and the calculator has been included to help with this task.
A great many exam-takers have been taught to use scratch paper to scribble down binary-to-decimal conversion charts and to manually convert entries back and forth. If you are doing this, you are eating up precious minutes that can be better used on other questions. This article will look at the calculator from the standpoint of the uninitiated, and show how you can use it to work through problems similar to those likely to appear on the exams.
First Look
The utility available during the exam is the same CALC.EXE that can be found in most
versions of Windows (9x, NT, 2000 and XP). When you first bring the tool up away from
the test center, it is in "standard" view, showing a simple 10-key calculator and not
of much use for exam purposes. From the menu bar across the top, selecting
View/Scientific changes it to the mode shown in Figure One.
The first thing to notice is that there are two sets of radio buttons. The rightmost set allows the choice between Degrees, Radians and Grads. The leftmost frame contains the choices for hexadecimal, decimal, octal and binary number sets. The rightmost set need never be changed during an exam while you can easily make changes on the right by clicking a different number set or (much better) knowing the associated function key (which start from the right):
F2 - Degrees
F3 - Radians
F4 - Grads
F5 - Hex
F6 - Decimal
F7 - Octal
F8 - Binary
NOTE: The choices in the right frame can change based upon the selected choice in the left frame. For exam purposes, memorize the F6 and F8 keys.
Working with IP
addresses
There are only two types of conversions that need be done with IP addresses-to binary
or to decimal. Again, you can memorize conversion tables and work out the math
longhand on your scratch paper or you can use the calculator and be surprised at how
much quicker it is.
To convert to binary, take each octet of the number you've been given (or only those that would factor into the solution) and convert them individually from decimal format. For example, with the address 209.16.14.110:
1. Make certain the Decimal format is the current format (or press F6 for good measure).
2. Enter 209.
3. Press F8. The binary equivalent (11010001) is returned. Note this on your scratch paper.
4. Press F6 to go back to decimal mode. Enter the second number.
Repeat steps three and four until all four octets have been converted from decimal to
binary.
To convert to decimal, reverse the steps. Very rarely will you need to convert all four octets, as this would be too time-consuming at most one or two octets would be given in this format. For example, assume you have the address 01101110:
1. Make certain the Binary format is the current format (or press F8 for good measure).
2. Ignore all leading zeros. Enter 1101110.
3. Press F6-the decimal equivalent (110) is returned. Note this on your scratch paper and repeat the process for any other numbers.
Working with Subnet
Questions
With the new exam, Microsoft has started using the /number format in many questions to
identify the subnet. For example, an IP range starting at 192.168.2.0 with a subnet
mask of 255.255.255.0 can be expressed as 192.168.2.0/24 since there are 32 bits in
the subnet and only 24 are used.
If you see an address such as 192.168.2.0/26, there are several things you should be able to do:
1. Express the subnet in decimal terms.
2. Identify how many subnets there can be.
3. Identify the number of hosts that can exist on each subnet.
Let's look at each of these three in turn, and start with the simplest. To find the decimal equivalent of the subnet:
1. Figure out how many octets are full by dividing the number by eight and looking only at the whole number. In this case, eight goes into 26 three times (you shouldn't need the calculator for this, but if you do, be in decimal format, enter 26, /, 8, = and then press Int.) With three full octets, you know the subnet is 255.255.255.x with "x" being the unknown.
2. Compute how many bits of the subnet are left over after step one. Without the calculator, you can subtract 24 from 26 and get 2 or, with the calculator, enter 26, Mod, 8, =.
3. Press F8 to go to binary mode. Take the answer from step two and enter that many ones followed by enough zeros to equal eight numbers. In that case, that is 11000000.
4. Press F6 and add the result to the answer from step one. In this case, the decimal value of the subnet is 255.255.255.192.
To compute how many subnets are available:
1. Take the number of bits used to create the subnet and subtract the number that would be used by default. For a Class A address (1-126 for the first octet), the default would be eight bits. For a Class B address (128-191), the default would be 16 bits. For a Class C address (192-223), the default would be 24 bits. Thus for the example, 26 - 24 = 2.
2. Press F8 to place the calculator in binary mode. Enter a number of ones equal to step one. In this case, enter 11.
3. Press F6 to get the decimal equivalent (three, in this case) and add one more to it (3 + 1 = 4). This is the maximum number of possible subnets for the values given.
NOTE: In the world of NT 4.0 exams, Microsoft would say only two subnets were available, whereas the answer is now four. This is because Microsoft now embraces RFC 1812 versus 950. This allows for subnets of all ones and zeros.
To find out how many hosts can exist on each subnet:
1. Subtract the number of bits in the subnet from 32. In the example, 32 - 26 = 6.
2. Press F8 to go to binary mode. Enter a number of ones equal to the answer in step one. In this case, that is 111111.
3. Press F6 to get the decimal equivalent (63 in this case) and subtract one from it (63 - 1 = 62). This is the maximum number of hosts that can exist on each of the subnets for the values used.
NOTE: You subtract one because host addresses (as opposed to subnet values) of all ones and zeros are still taboo.
Summary
The Scientific Calculator is available in most of the Windows 2000 exams and is the
only external utility you can use while taking an exam. Knowing how to use it and
master decimal and binary conversions can go a long way toward helping pass these
exams.
TIP: Values can be entered into the calculator by clicking on the number icons in the calculator or by the number keys if NumLock is on.
TIP: If you suspect a value will be used more than once, you can store the value by pressing MS and bring it back by pressing MR.