0:01 we're going to be looking at the first
0:03 section of the syllabus which is
0:05 information representation and the
0:07 subsection data representation the focus
0:10 for us today is going to be how and why
0:12 computers use binary to represent all
0:13 forms of data
0:15 now this is probably going to be a
0:16 rehash of some of the information that
0:20 you covered in igcse however
0:21 there are going to be some unique
0:23 aspects which obviously you need to know about
0:25 about
0:28 so let's start with the first difference
0:31 at igcse level you probably worked with
0:33 kilobytes megabytes gigabytes and
0:36 terabytes however at as level you'll
0:39 probably find that in industry there are
0:42 two terms that are used the first aspect
0:44 is the standard
0:46 international units which are kilo mega
0:49 giga and terra and then you have the
0:51 binary units
0:55 kibi maybe gb and tevi
0:57 the standard international units kilo
1:00 mega giga and tera
1:03 are normally based on base 10 so you go
1:04 up with 1000
1:07 you go to million you go to a billion
1:10 and trillion and when we look at kiwi we
1:13 go up in base two so this will be about
1:14 2 to the power of 10 which should be 1024
1:16 1024
1:18 and then similarly maybe will go up and
1:21 you end up with just a bit more
1:24 data than a million and a bit more than
1:27 a billion and then obviously a trillion
1:29 it is vital for you as a computer
1:31 scientist to know the difference between
1:33 both units and how
1:35 the everyday common person will probably
1:38 be using kilobytes and megabytes however
1:40 what the difference is with the actual
1:42 units and it makes a big difference when
1:44 you're dealing with memory for example
1:46 kiwibyte means you get a bit more
1:49 storage space a bit more space required
1:52 in the memory compared to kilobytes
1:54 so let's look at how two people will
1:56 deal with it so on the left hand side
1:58 we've got our amateur and on the right
2:00 hand side we've got our professional
2:02 their interactions together
2:05 based on what kibi is and what killer is
2:06 and how
2:08 confusing it all gets will give you an
2:10 idea of what challenges people face when
2:12 they're talking about
2:15 memory and storage capacity in kiwi and
2:17 kilobytes etc
2:19 so our amateur goes that okay i know
2:22 that computers work with electricity and
2:25 the expert as well computers actually
2:27 use binary and electricity can be turned
2:31 on or off so that is equivalent to base
2:34 two when the electricity is on we have
2:37 the digit one if the electricity is off
2:39 it's zero so the amateur is like okay well
2:40 well
2:43 i think that a thousand is a kilo and
2:46 that's a kilobyte
2:48 and the expert goes well in base two we
2:51 use something called geometric
2:55 sequencing so we go up in 2 4 8 16 32 64
2:58 128 256 and so on until we reach one or
3:02 two four and that is known as the kibi 2
3:04 to the power of 10.
3:07 so our amateur goes well
3:11 i still think mega is 1 million bytes
3:13 and the expert then goes well actually
3:16 it's 148
3:19 576 bytes which is also known as a maybe
3:22 byte so they're slightly different
3:24 even though for
3:26 small amounts
3:28 it's not a big difference but when you
3:30 create all these megabytes into bigger
3:33 numbers it can add up to a sizeable sum
3:35 our amateur goes well why the two
3:37 different approaches
3:38 and the expert goes
3:41 because of the si which is the systems
3:44 international units and to make it easy
3:46 for non-experts to remember all of these
3:48 these are called decimal prefixes or
3:51 base 10 prefixes so
3:54 prefixes are basically words which you
3:56 add in front of a number in this
3:58 particular case kilo is a prefix to
4:02 bytes and mega is a prefix to the bytes
4:04 so these are called dna prefixes because
4:07 they operate in base 10. the amateur
4:09 goes well now i am confused
4:12 gb is still gigabyte right
4:14 and the expert goes well yes that's right
4:15 right
4:17 however gib is
4:18 is
4:20 gibby byte
4:23 and a 1 gb hard drive will be smaller
4:24 than a 1 gib
4:26 hard drive because obviously there's a
4:29 lot more space in the gibby byte hard
4:31 drive version of things which is based
4:35 on base 2 and is a binary prefix because
4:37 it operates to 2 to the power of
4:38 something rather than 10 to the power of
4:42 something our amateur goes okay so one
4:45 tib is more than one tb or terabyte is
4:48 that correct and expert goes yeah you
4:50 got it one tabi byte is equivalent to
4:53 more than a trillion bytes or
4:56 1 trillion 99 million 511
5:00 627 776 bytes to be exact
5:02 so hopefully you've got a
5:05 good idea about what decimal prefixes
5:08 and binary prefixes are like and decimal
5:10 prefixes remember the term prefix means
5:12 adding something in front of a number so
5:15 in this particular case when we use the
5:17 standard metric system for prefixes they
5:20 tend to be kilo mega and giga
5:22 and the decimal system increases in
5:26 orders of thousands so 1000 gram is
5:28 equal to 1 kilogram and we use something
5:30 similar which most people are familiar
5:33 with in their day to day life
5:36 now why did this happen well it's
5:39 because consumer is king and this was
5:41 all great when storage capacities were
5:43 very tiny so in the old days we never
5:45 used to worry about like
5:47 megabytes and gigabytes
5:50 people used to work with bits and bytes
5:53 and storage capacities were so tiny that
5:56 decimal prefixes seemed normal
5:59 but as storage increased in size
6:01 unfortunately that caused a bit of a problem
6:02 problem
6:05 however still 1024 bytes was close
6:07 enough to a thousand bytes that we could
6:08 get away with things
6:11 but as memory capacity and storage
6:12 capacities increase things started to
6:14 become difficult for both software
6:17 developers and manufacturers themselves
6:20 so here's an example of this this is an
6:22 ad for a 10 megabyte hard disk in the
6:24 old days how do we know how big this is
6:29 is it 10 million bytes is it 10 485 760
6:31 bytes who knows
6:33 and that caused the problem for
6:34 consumers themselves as well because
6:36 they didn't know what they were paying for
6:36 for
6:39 or what did they get it was pot luck
6:41 and of course these days you probably
6:42 won't pay three thousand four hundred
6:44 ninety five dollars for a ten megabyte
6:45 hard drive these were expensive items
6:48 and it made sense to be exact
6:50 so what was the solution well the
6:53 solution of course was binary prefixes
6:55 the industry decided to get their heads
6:57 together and come up with a new prefix
7:00 system that uses binary units to avoid
7:04 all of this confusion and back in 2005
7:07 the ieee which if you came up on the
7:09 internet the institute of electrical and
7:12 electronics engineers and they came up
7:14 with this new standard so they said well
7:16 we're going to be using killer binary
7:20 mega binary giga binary and tera binary
7:23 which in short form become kibi maybe kb
7:26 and tevi the symbols are as what they
7:28 are so the bytes become instead of
7:30 kilobytes they become kiwi buys and so
7:32 on in an exam you might be asked to
7:35 equate between both of these units or
7:37 you might need to work out something in
7:40 megabytes or maybe bytes so when you're
7:41 working with megabytes and if that's
7:43 what the answer requires you do four
7:44 times a thousand times a thousand which
7:46 gives you four million and if you're
7:49 working with maybe bytes you go with
7:51 four times one thousand and twenty four
7:53 times one thousand twenty four
7:54 you've gotta be careful and you need to
7:57 check the required unit to work out what
7:59 the answer is
8:01 so are people actually using binary
8:04 prefixes well change is always very very
8:06 slow and if you look at operating
8:08 systems like microsoft windows you'll
8:09 probably see that microsoft is still using
8:10 using
8:14 bytes even though they're equating the
8:16 answers using binary prefixes they're
8:19 still referring to the end result as
8:22 deanery prefixes and this change is
8:24 prevalent throughout the industry
8:26 however people are trying to change step
8:29 by step things will change
8:30 at this particular point in time you
8:32 should try your hand at this particular
8:34 worksheet see if you understand the
8:36 difference between both decimal and
8:38 binary prefixes
8:40 and you should try to work this out
8:42 physically instead of using a calculator
8:44 perhaps use 2 to the power of 2 or 10 to
8:47 the power of something to to get those
8:50 longer calculations shorter
8:52 there's a few questions on screen which
8:54 should take you about 10 to 15 minutes
8:57 to do so have a go pause the video
8:58 and perhaps
9:00 see if you can apply
9:01 apply
9:03 what you've learned so far by solving
9:05 these questions
9:07 some of the key terms that we've used so
9:09 far are binary which is a base two
9:12 number system zero and one only
9:14 bits which are obviously short form for
9:15 binary digits
9:18 and obviously the terms binary prefixes
9:20 and dna prefixes which are a set of
9:23 letters that proceed a unit of measure
9:24 such as a byte and
9:25 and
9:26 the binary one
9:28 indicates multiplication by a power of
9:30 two and d
9:31 indicates multiplication by a power of ten
9:32 ten
9:35 and another word that is quite common is
9:37 what the magnitude of a number is and
9:40 that's the actual value of the number
9:42 okay we'll stop the lesson here for today
9:43 today
9:46 hopefully by now you're familiar with
9:48 the syllabus itself and if you're not i
9:49 would probably suggest download it and
9:50 have a look through that
9:52 you've completed a worksheet if you
9:54 haven't please go back and do that it's
9:55 very useful to practice these i'll try
9:58 to put these type of questions in future
9:59 videos as well so so you can just
10:02 practice what you're learning and of
10:04 course have you signed up to ripple.it
10:06 and if you have fantastic the other
10:08 thing i want to add here is that you
10:11 might want to start an exercise book for
10:13 note keeping and perhaps use the cornell
10:16 note-taking system it's fantastic it's
10:18 proven to be one of the best ways to
10:21 summarize knowledge look it up
10:24 it's just fantastic that's all i'll say
10:26 okay that's all for now and we'll catch
10:28 up in the next session which will be
