this video is sponsored by keoxia
solid-state drives are fascinating not only because they can store terabytes of data
but because they can access any piece of that data almost instantaneously this solid state drive
can hold eight terabytes of data if each bit were represented by a penny faced either heads or tails
that is a one or zero this drive could store the capacity of 64 trillion pennies now if we laid all
of these 64 trillion coins out flat on a surface the area of the surface would take up the entire
state of massachusetts which is an incredibly large area to be covered in pennies but what's
truly incredible is that the solid state drive can find a five by five meter area of pennies anywhere
on this massive surface and then right to or read out the binary state of those pennies
in fact the ssd can erase and change the state of every single one of these 64 trillion coins up to
10 times every day and it can read out the state of all of these pennies around 70 times a day
so how does it do it well in this solid state drive there are 18 nand flash microchips that
are used for storing all eight terabytes of data when we look inside a single chip
we find that there's a stack of eight die each die has two planes and if we were to zoom in on
a single plane we would find that each plane is a vast array of vertically stacked charge trap flash
memory cells organized into thousands of blocks each block is organized into hundreds of pages
and each page contains tens of thousands of memory cells and each charge trap flash memory
cell can hold three bits of information or three coins worth of data here's a nanoscopic picture
of what the stacks of memory cells look like which is just one microscopic section of the overall dye
in other episodes we discussed how information is stored in each cell or how the pages of cells
are organized but for this episode let's focus on the big picture and see how the solid state
drive can store 64 trillion bits and how it can access or write to the contents of just one
page of about 10 million pages note however that these numbers are approximate and that they're
different for different brands and sizes of ssds in this solid state drive there are a number of
components we have to look at first over here is the ssd controller microchip or brain whose role
it is to interface between all 18 nand flash chips this microchip also interfaces and communicates
with the laptop computer or server that the ssd is plugged into aside from the 18 nand flash chips
and the controller the other main components are the 8dram chips which serve as a memory buffer for
holding the massive lookup tables or translation tables that tell where all the information is
stored we'll get into what this lookup table does shortly but for now the other main components are
the memory channels that allow the 18 nand flash chips and the ssd controller to communicate
each nand flash chip has a memory channel and is composed of 16 wires or traces
that run through the pcb these memory channels are used for reading the address of where data is
located and transferring the actual data to write to or read from the nand flash additional traces
are used for sending commands to write to or read out the information to each of the nand flash
chips to better explain the data flow let's use a simple example the computer requests a small piece
of information from the solid state drive say a picture the ssd controller then sends the request
for the nand flash chip to read out the contents of chip 9 die 4 plane 1 block 351 page 45.
the 3d nand flash chip accesses that location and sends the contents along the memory channel's 16
traces back to the controller this controller then routes the information to the computer that it's
plugged into or the reverse could happen where in the computer asks to store data the ssd controller
would then ask the nand flash chip to write the information to a particular page or if the file
were larger the controller would write this file to hundreds of pages instead of just a single page
you might wonder how does the controller keep track of where all the information is stored
well that's the role of the lookup table or the translation table from the perspective
of your computer the ssd is just a massive set of sectors of data each the size of 512 bytes
and thus this 8 terabyte drive has 15 billion sectors for example when you store a picture
your computer tells the ssd to store the picture's data in a set of unused sectors the ssd controller
then takes the picture's data and sends it noting the address for the chip die plane block and pages
of the precise location the ssd controller essentially has a massive spreadsheet where
all the sectors are translated into different locations inside the 18 different nand flash chips
note that this type of translation is also called a logical to physical translation where your
computer only sees what sectors the picture is stored in but the ssd knows the physical locations
furthermore the translation table or lookup table is continuously being updated when it's
in continuous use it can be found in the working memory or dram chips of the solid state drive
and when it's not in use it's saved to the 3d nand flash chips another important detail is that while
individual pages can be written to or read from it's more common for super pages to be utilized
a super page consists of all the pages on each of the 18 chips that share the same die plane
block and page designation and thus the super page has the same address in each of the respective
18 nand flash chips for example when a large video gets saved it gets spread across all 18 nand flash
chips and stored in a super page or possibly multiple super pages thus when writing to or
reading out the video all 18 chips are running in parallel resulting in read or write times
faster than if the video were stored in just one of the nand flash chips furthermore super blocks
can also be utilized and they're the common block address among all 18 nand flash chips also note
that the ssd controller performs other functions like wear leveling garbage collection
and executing the error correction code but these topics will be saved for a future video
this is the fourth video that explains how solid state drives in 3d nand flash work
this video focuses more on the ssd architecture while the other videos explain the structure of
the 3d nand flash how information is written to a cell and how information is read from a cell
check out those videos as well this video is sponsored by kioxia as you may have noticed
this is a chaoxia ssd and there's a lot of engineering that goes into it
the oxia sells a wide variety of ssds and the one we're using here is a data center class
ssd which is designed for consistent performance and latency for hyperscale applications they
also provide enterprise ssds which are top of the line ssds in terms of read and write performance
and reliability check out keoksia's ssds using the link in the description we'd like to thank all of
our youtube and patreon sponsors for helping us build these in-depth engineering explanations
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