Data Representation

The first video explains why computers use binary to store data.  The difference between a bit, nibble, byte, kilobyte, megabyte, gigabyte, terabyte and petabyte is explained.  These are known as measurements of capacity, or how much data can be stored either in memory or on secondary storage devices.

The second video explains how to convert between the base ten denary number system that we are familiar with as humans, and the base two binary system that computers use.  This explains how computers store unsigned integers.

The third video explains how an arithmetic logic unit can add two 8 bit binary numbers together.  The concept of an overflow error is also discussed.  The electronics needed to create these circuits is explored further at A’level.

An arithmetic logic unit is also capable of “binary shifting”.  That is moving the binary digits in the accumulator to the left or right a given number of spaces.  In effect this either multiplies or divides the number by a factor of two, but in reality it is used to access and change individual bits in a series.  This is useful when the binary stored is not really a number, but represents something else.  This often finds uses in low level programming because micro-controllers and microprocessors rely on the values of individual bits for particular operations.  The fourth video provides a brief introduction.

Large binary number sequences become difficult to manage, so we often use hexadecimal, the base sixteen number system to represent nibbles of data in one symbol.  The fifth video illustrates how to convert between denary and two-digit hexadecimal.

Check digits are a simple mechanism to verify that data has been entered correctly before being transferred for further data processing.  The sixth video illustrates how check digits work.

A defined list of characters that are recognised and can be stored in a computer system is known as a character set.  The seventh video explores the ASCII, extended ASCII and Unicode character sets, explaining their relationship to binary and the number of characters in each set.  The need for different character sets and how these have evolved over time is also explained.

The eighth video explains one technique for how binary can be used to store images.  This technique is known as bit-mapping.  The smallest part of an image, known as a pixel has a binary code for its colour.  This video explains the relationship between the number of pixels, the number of colours and file size of the image.

The ninth video explains how sound can be represented and stored in binary.  A number of key terms are defined including sample size, bit depth and sample frequency together with the impact they have on both the quality and the file size of a sound.

The tenth video explains the need for, and types of compression.  Lossy and lossless compression are explored with their advantages and uses.

Resources:

https://student.craigndave.org/videos/ocr-gcse-slr2-6-units

https://student.craigndave.org/videos/ocr-gcse-slr2-6-converting-between-denary-and-8-bit-binary

https://student.craigndave.org/videos/ocr-gcse-slr2-6-adding-two-8-bit-binary-integers

https://student.craigndave.org/videos/ocr-gcse-slr2-6-binary-shifts

https://student.craigndave.org/videos/ocr-gcse-slr2-6-converting-between-denary-and-2-digit-hexadecimal

https://student.craigndave.org/videos/ocr-gcse-slr2-6-check-digits

https://student.craigndave.org/videos/ocr-gcse-slr2-6-characters

https://student.craigndave.org/videos/ocr-gcse-slr2-6-images

https://student.craigndave.org/videos/ocr-gcse-slr2-6-sound

https://student.craigndave.org/videos/ocr-gcse-slr2-6-compression

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This resource is part of Craig ’n’ Dave OCR GCSE Computer Science

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