So I thought we'd look at today is how do pop adidas hardest tape store information they all store the data
but in terms of electrical signals in silicon, but as
basically magnetic data stored on bits of spinning rust
So what I've got here is a five and a quarter inch
Floppy disk this one's got a copy of small talk on it
Probably for PC. It's what small talk small. Talk is the the classic
Object-Oriented programming language then what about object-oriented programming then look at one of our arrow videos
This is not the word saver icon. This is actually a three and a half inch floppy disk
Which is what people are probably more familiar with?
Essentially this and this work in exactly the same way
That's just easier to see what's going on and why they'll call floppy with one of these when these are produced they put a protective
Hard case around the floppy disk and a mental cover to protect the actual floppy
Information there so it's easy to see why these are called floppies if you actually take them apart and here's one
I destroyed earlier. This is a five and a quarter inch floppy
They're also eight inch floppies, and if you actually take it apart, you'll see this is a sort of protective plastic case there
We are in and inside that there is a sort of material thing that's actually there to protect the floppy disk
Which is this bit, so when the iBm originally created the floppy disk?
They originally just had the floppy part like that
But they found that dirt and things would scratch it and Destroy the data
So they put it in a protective case so that only the readwrite area was exposed to protect the data and the material side
Just sort of mopped up any adjuster got in there and stopped it scratching the data and it is literally just a piece of plastic
coated in
Effectively rust is probably a cobalt based compound rather than iron, but it's basically rust. It's magnetic data
I knock so
Just like a classic cassette tape or a video tape that you may have used so what have we got well we've got a magnetic
Material and the way the computer would use this is actually easier to see with
tape
so computer tape
effectively, the same sort of things is a classic tape you may have seen these in sort of old movies sort of sitting in the
background turning
and that's exactly what they did if we take the
Casing off you have an even thinner even floppy a piece of tape than the actual
Proper disc and you can start to see why tape is even still used today because it just holds so much data
you think about it the amount of
surface area that you can write to on a floppy disk is only going to be a small amount of
Tape that you need to store the same thing and yet if you think about the size of this you can get a lot more
tape
Into the same area well that's someone else do the math on that so you have
the tape and you have one side of it got all your data on and another one going to the take-up spool just like an
Old reel-to-Reel audio cassette and then you would have a head and I'm going to use the pen to represent the head of the machine
Which would sit in contact with the tape and the tape would be pulled
across the head as it was
Transferred from one spool to the other and that head could either read the data that was on the tape or write the date on
The tape and how is actually arranged depends on the tape format?
We won't go into the details, but you could basically store bits of information
Sequentially on the tape so you start off with the first bit here say than the next bit and so on and as you read
through the tape you would store more and more information as I said the
Order on the actual day two depends on the tape format
This is general principle and as you read through it you get more and more the data
Was it would it be one one-line thick or would you be using multiple tracks?
There was various different formats. I mean this is nine track tape
I think I'm not entirely sure what you sort of had nine track
Tape formats you had other ones some of them use helical scan were actually the head is spinning itself and so it's writing stripes
across the actual tape like a video cassette does
These various things some are linear when they're ready writing in that though actually it literally depends on the tape format most common one today
Is called Linear tape whether it's actually still linear
I am not certain
So you can store a lot of information on this
But you have to access it effectively sequentially you have to start at the beginning and move through to the end before you can get
To any information that you want on it
Which of course takes time if you want the information right at the end here you?
Have to spill out all the information on the tape
and you can do this relatively fast and
Shawn's going to wind all this back up later
So only works you have to access things sequentially you don't have easy random access to the data
You could do it
You could get the computer to sort of work out where how far needs to fast forward and then put markers in the data
So you can find different bits, but you still have to wait while it gets to that point?
To access it
What we disk work?
In Roughly the same manner to record Data. I've got a floppy drive here which I've taken apart
Eagle-eye viewers may recognize it you still have
The heads just here the disk is
Popped in and you manually have to close the thing down to lock the disk in place
And then there's a motor which spins the disk ground
So the disk is spinning round and round around very fast like a cD does so the really important thing is that the head?
Can move backwards and forth?
Over the top of the floppy so we have two axes of movement here
We have the disk spinning, and it'll go in One direction
Let's go that way which means that the head is getting the data in a loop
So it'll get some of the data as it goes around and round around around and they'll come back again
you can start getting the data again, but the head can also move backwards and
forward along
The dryer which means it can step out or step in to different parts of the disk and so get a different loop or different?
Trackers, they're known of
Information from the disk if I can draw a circle which I can't hurry up, so this is a disk
So we've got the head going up and down which means it can draw
Tracks around with this as I said I can't draw circles. Just one more and so the head can step out
To each of these track and read a different set of data
at each of these different points
So protocol this track 0 this would be track 1 this would be tracked - this is the track 3 and this would be tracked
4 so we've now got 5 tracks of information where we can store data
So where's on tape we have one long piece of information?
And we have to scroll backwards and forwards in it with a disk we have lots of small
tracks of information, but the sort of consent along the disk surface
And we can step our head to read one of these tracks and because the disk is spinning
probably with a floppy like one of those at 300 rPM with a modern hard disk which works in exactly the same way at
7,200 rPM. We very quickly get all the data that's stored on their path under the head in one go so we can specify
Which track we want to read the data from and we can move our head to the right point?
But we actually go one step further because we actually break the data up into what we call sectors like so
And then hami ok I'm not an artist looks like a giant spider's web. It's not yeah
I mean, it's the same thing you bisecting the
Circle into several slices, we've got 1 2 3 4 5 6 7 8 9 10 we have 10 sectors
So we say that the data we want to access is on track to
Set to 8 and we go to Track 2 and we wait as this spins around until we get the data for
sector age Read across
and then we might say we actually want the data from track for sector worn so we wait until
the Data for sector 1 of Track 4 comes across
So if we go back to the drive if we put the disk with our drive on a diagram here
And we eliminate it. We've got the sector's around here. The disk is spinning
Very very fast so the head just moves
Backwards and forwards and say so it's down there their position for track 1 and it waits until sector
To say comes across reads the data and then send it out to the computer or take the data from the computer and write it
Onto the floppy and so because of that we can access any particular sector of data
We want to on the disk because of the nature of a circle surely the inner tracks store less data than the outer tracks
so yes
They will or maybe they won't it depends on how the disks formats the information a standard sort of PC floppy
The inner track store as much data as the outer tracks because the disk is spinning
it's not
Distance it's an angular velocity, not air
So it's got a constant angular velocity
So it takes the same amount of time to go around once all that means is the data is packed into a smaller thing
But it out at the same speed it probably means the Data is more
Likely to get corrupted on the inner tracks rather than the outer tracks on something like a five and a quarter inch floppy
Probably depending on the type would either be storing
256 Bytes, Maybe
512 bytes of Data in one Sector of the same on a three and a half inch floppy you'd have
512 byte Sectors, and actually your hard disks work in exactly the same fashion
they have
tracks
They have sectors and they also have different heads and the other thing you get in the hard disk is you just have multiple platters
And the reason they're called hard is because they're made out of things like glass rather than after flexible bits of plastic
We keep carving away at this and what we'll end up with is something that looks nearly like a cube
So we probably may be a bit a bit of extra there and a bit of extra there and there, but we'll get it
We're getting there, okay. Now some objects obviously are more amenable to miss than others, but the more images we get the better it is