Data Representation

Data Representation covers number bases, binary and hexadecimal conversion, binary addition and shifts, units of information, character encoding, images, sound and compression.

Everything rests on the place values, so write them out before converting anything. Hexadecimal conversion works because one hex digit is exactly four bits, and grouping must start from the right — grouping from the left gives a wrong answer whenever the digit count is not a multiple of four. File size calculations follow fixed formulae but the marks are lost in the unit conversions: the result arrives in bits, so divide by eight for bytes and then by a thousand for kilobytes. Sound calculations need the duration in seconds. Compression questions expect the lossless and lossy distinction stated precisely.