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Degree: MSci Computer Science with International Year Abroad (Masters) - Nottingham University
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Ed (Student) April 14 2016
The sender's role is to add the parity bit. ASCII characters are represented using a 7-bit binary string. A parity bit is added to the beginning of the binary string (i.e. at the most significant bit, or MSB). Since it's even parity, the number of 1's in the 8-bit binary string must be even.
For example, if the sender wanted to transmit the ASCII code for the letter 'A' (ASCII code 65), which is represented in binary as 1000001, a 0 would be added as the parity bit at the MSB. Therefore, 01000001 would be transmitted.
Similarly, for ASCII code 'C', which is represented in binary by 1000011, a 1 would need to be added to make the number of 1's even. In this case, 11000011 would be transmitted.
The receiver's role is to check that the number of 1's in the received binary string is even. If the binary string fails this parity check, the received will ask the sender to send the data agin.
For example, if 01000101 was received, this would fail the parity check; the number of 1’s in the binary string is not even, so the data would have to be resent. However, if 11000101 was received, then this would pass the parity check, meaning that it’s likely (though not necessarily guaranteed) that the data has been received as it was sent, and has not been corrupted.see more
An intractable problem is a problem that is solvable, but not in polynomial time or less. Such problems cannot be solved in time considered to be reasonable (i.e. not solvable quick enough to be 'useful').
Let's start by looking at the denary (i.e. base 10) number system. In base 10, you have a column for each digit in a number.
For example, with the number 5,867 you have a 5 in the 1,000's column, an 8 in the 100's column, a 6 in the 10's column, and a 7 in the 1's column. Essentially, this means: (5 x 1,000) + (8 x 100) + (6 x 10) + (7 x 1), which of course comes to 5,867.
The same principle can be used for hexadecimal to denary conversion. Hexadecimal uses the base 16 number system, so instead of have a column for 1's (100), 10's (101), 100's (102) etc. you have a column for 160, 161, 162 etc.
Hexadecimal uses numbers from 0-9 followed by A-F (i.e. 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F) to represent their denary equivalent 0-15. The letter A represents 10, B represents 11, and so on up to F which represents 15.
So, for the hexadecimal value A7, we have a 7 in the 160 column, and an A (which as we know represents 10) in the 161 column. Therefore, to convert it to denary, we do:
A7 = (161 x 10) + (160 x 7)
= (16 x 10) + (1 x 7)
= (160) + (7)
Therefore, the hexadecimal number A7 is equal to the denary number 167.see more