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  • How do Smartphones Store Data? || How do SSDs Work? By Branch Education

  • It's hard to believe that all your photos, videos, music, messages,

  • and apps can be stored in the palm of your hand,

  • and to most of us it's a mystery how so much information

  • can fit in such a small space.

  • But it might not seem so surprising when you see

  • the complexity inside your smartphone,

  • or the inside of this one terabyte solid state drive

  • commonly found in laptops or computers.

  • However as seeing the outside of this memory storage microchip

  • tells us little about how these smartphones

  • and solid-state drives can store tens of thousands of photos

  • and files, let's explore deeper and zoom in until we get

  • to a nanoscopic view, and it's here that we can see the structures called

  • VNAND that hold all the data in your smartphone and computer.

  • Here is where the real magic happens.

  • Every picture, message, and bit of information

  • gets saved as quantities of electrons

  • inside these memory cells which are called charge trap flash

  • and, in this episode, we'll learn how smartphone memory and solid-state drives work.

  • Now, hold on- these insanely small and intricate structures seem very complex,

  • and yeah- they are- I'm not going to say this marvel of engineering is simple.

  • But you have to trust me- stick around,

  • watch closely, maybe watch this video twice,

  • and by the end of it, this technology will amaze you,

  • it will blow your mind at least twice over, and yeah, you'll have

  • a thorough understanding as to how such a small device,

  • can store weeks of high quality video, tens of thousands of pictures,

  • or hundreds of thousands of songs in such an itty bitty little space.

  • So, let's get started.

  • We're going to use a real-life example and

  • explore how it works when you save a picture to your smartphone or computer.

  • First, this picture is made up of pixels

  • and each pixel has a color so let's zoom in so

  • that we can see the individual pixels.

  • The color of every pixel is defined by a combination of 3 numbers,

  • ranging from 0 to 255, each representing red, green, or blue.

  • For example, the numbers would be 55-53-55

  • for this pixel's color right here,

  • and then 124-121-119 for this pixel.

  • Each of these 3 numbers from 0 to 255 is represented

  • by 8 bits in binary, or eight ones and zeros ya know,

  • because computers work in binary.

  • So, 3 colors, red, green and blue, and 8 bits each,

  • means each pixel takes 24 bits to define its color.

  • This picture is a grid of colored pixels,

  • so let's turn it into a grid of values, kind of like a spreadsheet in excel,

  • but called an array instead of a spreadsheet.

  • This array of bits is what your computer cares about and noncoincidentally,

  • it's also the information that the camera on my smartphone

  • recorded when I took the picture.

  • One quick note: if you want to see the pixels in any picture,

  • just open it in an image editing program like paint

  • or 3D paint in this case, and zoom in.

  • And then if you want to see the red, green and blue

  • or RGB values, just use the eye dropper, click on a pixel,

  • and then click on the edit color option.

  • Right here you can see the 3 values

  • for red, green, and blue, and the resulting color.

  • Ok, with that covered, let's get back to this episode,

  • first, we're gonna zoom out to see the full picture,

  • which is 3024 pixels wide and 4032 pixels tall,

  • which is a total of around 12 million pixels, or, 12 megapixels-

  • which relates to the resolution of the 12 megapixel camera on my smartphone.

  • Next, by doing some multiplication

  • we calculate that an array of this size,

  • where each pixel is defined by 24 bits,

  • or 24 0s or 1s only requires 293 million bits

  • or a unique set of 293 million 0s or 1s.

  • That's a ton of bits, so let's figure out how your smartphone

  • or this solid-state drive seamlessly

  • stores every single one of them.

  • Ok: so let's open up that solid state drive again

  • and zoom into a simplified nanoscopic view

  • kind of like the one we had earlier.

  • It's here that we can see the memory cells

  • that are used in every single one of your smartphones or tablets,

  • as well as inside the solid-state drive in your computer.

  • This is the basic unit of a computer's long term memory storage

  • and it's called Charge Trap Flash Memory-

  • so how does it work?

  • Well, in each cell we can store information by placing different

  • levels of electrons onto a charge trap,

  • which is the key component inside the memory cell.

  • Older technology could only store two different levels of electrons,

  • a lot of electrons or very few electrons,

  • which were used to store a single bit as a 1 or a 0.

  • However, engineers have been developing more finely tuned capabilities

  • for trapping and measuring different amounts of electrons

  • or charges onto the charge trap.

  • Most memory cells in 2020 can hold 8 different levels,

  • but newer technology can have 16 different levels of electrons.

  • This means that a single cell,

  • instead of holding only one bit as a lot of electrons or no electrons,

  • can now hold 3 or more bits

  • but, for this example, let's stick with 3 bits.

  • So- in this cell, if we were to have very few electrons on it,

  • it would be 1-1-1, while some electrons get designated as 1-0-0

  • and a lot of electrons are 0-0-0

  • There are 8 different levels for all the various amounts

  • of electron charges that our charge trap can be set or written to.

  • The key to the charge trap is that it is specially designed

  • so that after it gets charged with electrons,

  • it can hold onto those electrons for decades,

  • which is how information is saved or written to the solid-state drive.

  • I mean- it's called a charge trap for a reason.

  • It traps electrons, or charges for years on end,

  • and in order to read the information,

  • the electron charge level is measured,

  • and the amount of charge on the charge trap is unchanged.

  • However, in order to erase the contents of a memory cell,

  • all the electron charges are forcibly removed

  • from the charge trap returning it to its lowest level,

  • which is 1-1-1, and leaving no excess electron charges behind.

  • Let's move on and explore how these memory cells are organized

  • so that we can store more than just 3 bits of information.

  • After we zoom out a little,

  • you can see that the memory cells are stacked vertically.

  • This is where the vertical part in Vertical NAND or VNAND comes from.

  • This stack of memory cells,

  • what is technically called a string is composed of 10 charge trap flash cells

  • layered one top of another.

  • when information is written to or read from a string,

  • only one cell can be activated at any given time,

  • and to do that we use separate control gates

  • attached to every layer in the string.

  • It works like this: the bottom control gate first says

  • Hey you, charge trap 1 what's your electron charge level at?”

  • Then the bottom cell sends that information through

  • the center of the string up to the information highway at the top,

  • which is technically called a bitline.

  • Then the next control gate for the 2nd layer

  • asks for the charge level in the 2nd cell, and so on,

  • up the string, each cell sending their

  • information up to the highway or bitline.

  • The same kinda sequence happens when charges are being added

  • to a charge trap which is how information is written to a memory cell.

  • The main thing is that only one layer in the string

  • is either written to or read from at any given time.

  • Let's move on in complexity, next we duplicate this string 32 times,

  • and this gets us a page of strings.

  • Let's review some terminology:

  • this a memory cell and this is a string.

  • And now here we have a page, and we are going to call this entire

  • page of strings a row. When we duplicate the string,

  • we also duplicate the bitline 32 times,

  • however rather than duplicate the control gates,

  • we are going to have every cell in the same page

  • share a common control gate.

  • This makes it such that when information is written

  • to or read from a row,

  • an entire page composed of 32 adjacent cells,

  • all in the same layer, are activated at the same time.

  • Let's step up in complexity again:

  • Next, we duplicate these rows 6 times until we get a block,

  • but we are going to do it 12 times so we can see 2 blocks.

  • Okay, so again, here we have a column,

  • here is a row, this is a layer. And now here is a cell

  • and here is a string. Next we have a page,

  • and finally we have a block. We are going to connect the tops

  • of each string in a column together,

  • so they all share the same bitline

  • and our bitline is looking more like a highway now.

  • In addition, we have to add a control gate that selects between rows,

  • so that only one row is using the bitline at a time.

  • These are called bitline selectors.

  • As discussed these bitlines are like highways,

  • and the selectors at the top act as traffic lights that

  • mediate the flow of information

  • so that only a single row can use the highway,

  • or is active at a time. Similarly, the control gates attached to each layer

  • act as traffic lights for the layers.

  • With bitline selectors along the tops of each row,

  • and control gate selectors along each layer,

  • the solid state drive can read from or write to a

  • single page at any given time.

  • Additionally, in order to connect to the bitline selectors

  • and control gate selectors there are wires that drop down from above

  • and run perpendicular to the bitlines.

  • So, let's quickly recap:

  • 8 different levels of electrons are placed on charge traps

  • in order to store 3 bits of information.

  • These charge trap flash memory cells

  • are stacked into strings 10 cells tall,

  • which are duplicated into pages of 32 strings in a row.

  • Next, those pages of strings are duplicated

  • until we have a block 6 rows deep,

  • and here we are showing 2 blocks.

  • Doing some quick multiplication we find that there are

  • 3,840 memory cells here

  • capable of storing a total of 11,520 bits.

  • With each pixel in our picture requiring 24 bits,

  • that means that we can store 480 pixels,

  • or this much of our overall picture.

  • That means you need about 25 thousand times the size of this layout

  • to store the contents of this single picture.

  • Aaand, here's where we learn about the actual size of a memory chip.

  • All the principles we have discussed remain the same,

  • so keep those in mind, it's just that the size is much more extensive

  • than we discussed in our example.

  • It's hard to pin down exact numbers because

  • manufacturers are continually improving their designs

  • and they are very secretive regarding what their designs look like.

  • But I'll tell you what I know:

  • the latest designs utilize not 10 layers as in the example,

  • but rather somewhere around 96 to 136 layers tall.

  • Here's a single sheet of paper so you can get

  • a sense of the of the approximiate height

  • of these stacks of memory cells.

  • Now that we understand the height, lets think about the width.

  • A page is around 30,000 to 60,000 adjacent memory cells wide.

  • That means there are 30,000 to 60,000 bitlines

  • in our information superhighway.

  • Blocks are every 4 to 8 rows

  • and there are around 4000 to 6000 blocks.

  • Along the edges are the control gate selectors

  • and the bitline selectors on the other side.

  • Together, they comprise what is called a row decoder,

  • and by using both sets of selectors as traffic lights,

  • we're able to accesss a single page.

  • To repeat this, only one page, 45 thousand or so cells wide,

  • ever uses the bitline to read or write information at any given time

  • All tens of thousands of bitlines

  • feed down here to the page buffer

  • where the information from a single

  • page is written to or read from.

  • Let's transition to see what an overall chip might look like.

  • Here we have the arrays of 3D memory cells,

  • the row decoder and the page buffer at the bottom.

  • Additional peripheral circuitry can be found here for supporting the chip.

  • In order to fit more capacity, engineers copied this layout onto the other side.

  • This chip can read or write at a rate of around

  • 500megabytes per second. That means that it can read from or write to

  • around 63 blocks every single second.

  • That's incredibly fast!

  • Ok, let's add the last level of complexity.

  • Engineers like to fit even more stuff

  • in as small of a space as possible,

  • so on top of having a massive array of memory cells

  • in this insanely complex layout,

  • they decided to copy this chip 8 times.

  • and stack it into a single microchip.

  • At the bottom, an additional interface chip is used

  • to coordinate between the 8 different chips.

  • And that's it, that's all there is in this one microchip

  • that can found at the center of every

  • one of your smartphones, tablets, or solid-state drives.

  • This video covered a lot, and I hope you kept up.