i've been like talk recently about
soc system on a chip system on a chip
yeah absolutely
why are people going in that direction
it seems to be everyone's using system
on a chip so i think it's it's worth
starting by actually looking at what a
system on a chip is what do we mean by
system on a chip and then we can start
to talk about why that is becoming more
popular when we do it
so to understand systems on a chip i
mean because they are literally
everywhere it's probably helpful to look
at an early example of that of using it
in a computer now systems on a chip
aren't just using computers obviously
mobile phones are built around systems
on a chip look let's be impartial here
even google ones are built around system
on a chip somewhere down here in the
archive
i have an acorn a310
machine this is dating from around the
early 90s 92 possibly maybe 93 and
things let's whip the lid off
get rid of the keyboard
and we can actually see that
there's very very little
inside this machine
even less in it now very very little
inside this machine we've got the power
circuitry over here which we're going to
have to have power for the floppy drive
let's just get that out of the way we've
got a tv modulator so you can plug it
into your tv we've got some memory we've
got the operating system built into rom
and the only other chips that are on
here apart from a few buffers to do
things like the printer port is we've
got the chip that handles the floppy
disk and the hard drive and things
another one down here suspect is the
keyboard controller and then we've got
one chip here
and actually this is the whole computer
effectively everything that you need to
build the computer is now on this one
silicon chip that was built by arm which
would spun out of acorn
in around
1992 in fact it says until week 47 of
1992. so literally
29 years ago today almost so that sort
of time when we're filming this in
mid-november
in 2021
other years are available if you're
watching this at a later date yeah i
think this is week 46 actually so yeah
yeah that's week boys yeah so actually
yeah so so everything was built into
that one ship we've got the memory
outside we've got the operating system
rom outside the controller for the
floppy disk and the serial port and the
printer port and things
but everything that forms the computer
is in there
now okay so we've got a system on a ship
what's that different well let's look at
what
a computer from a bit earlier same type
of computer system around the same
operating system same sort of memory
same facilities let's look at the
original acorn archimedes of which this
is derivative which is slightly bigger
and slightly heavier
which is the acorn 8310 machine if i
pull the motherboard
out
of this one without destroying it we can
see
a much bigger difference between the two
of them so this is from late 87 that
this machine was designed when this
machine was actually built is another
matter so this one probably does date
from around 1987 yeah i'm seeing 87 on
quite a few chips on here so this
machine 87 week 24 for that one this
machine dates back to
1987. but acorn continued to sell this
machine up until about 1990 i think
then launched the a5000 machine which is
over there and a couple of days later
this one came up but technologically
these are the same machine the cpu is
the same architecture of the cpu and
things it all works the same the
operating system is in the same things
but if we compare them
obviously the power supply is separate
on there but that's just doesn't really
matter
we can see that rather than just having
a single chip
and the operating system and the ram
we've actually got four huge chips that
are on here there's the floppy
controller that's the serial controller
the parallel supports built by some of
these around here and so we've actually
got four chips on here that build the
computer compared to the single one that
builds it here so actually what they
acorn did was they took
the design for their archimedes computer
which was built around four chips so you
had the the arm cpu which is down here
this is the arm2 cpu the original arm
chip everything that comes after it
sean's mobile phone the iphone the m1
all derived back from this well i'm also
the arm one that came before it so you
have this which was a cpu
but you also needed
a chip to handle the video which i think
is that one please don't spam me in the
comments if i've just hit the wrong chip
one that supports io and handling that
and then one that handles the memory and
so it was built up as a suite of four
chips that worked together this did the
processing and things and then it would
send requests over the address bus to
fetch or store data over the data but
coming out of this chip you've got
series of parallel wires that form the
address bus and the data bus and it's
probably similar on the other side and
so on if we were to count them
there's probably in the region of about
32 of them coming out
of here and we can see that these are
all connected to the memsi chip the
memory controller here so the complete
computer system was built out
of four chips that all had to be linked
together and when you designed the
computer system you had to take 32 data
lines that made up the data bus and
connect them to where they need to go
you need to get 26 lines that made up
the address bus and connect them where
they need to go and so you ended up with
huge amounts of
parallel data wires connecting things
together to make sure
everything worked so these chips working
together made it into an archimedes
computer you could take the arm chip on
its own and pair it with different
things it would still run arm code
but it wouldn't be
an archimedes as such you wouldn't be
able to drive the graphics in the same
way if you had a different graphics chip
in there it would work
in a different way so our system was
built up of all of these components yes
we had some extra things around it to
handle things like the floppy drive you
could have an optional hard disk on
things and so on serial port but the
main things that form the computer were
the video controller the i o controller
the memory controller and the arm cpu
itself so that's what the system is made
of that but what acorn did
was they took the design for all of
those chips and they integrated them
together onto this single chip
and so what you connected to the edge of
here were still the same things but they
only had to go to the memory in the
operating system and they only had to go
to the chip that controlled everything
else and so it simplified the design of
the system if you look at the number of
wires
coming off here you've got wires snaking
all around the motherboard to get to the
various place on both sides
of the thing if you look at the same on
this one it becomes a lot simpler we've
got the wires are going off to the ram
and the rom over there the wires are
coming off over here to connect up to
the interface and things so it's a lot
simpler to design what's going on a lot
of the interconnections that are needed
between the different chips that make up
the system
can be sort of they're still there
they still exist but they're all
integrated
into the one ship and so the computer
design becomes a lot simpler one ship
connected to what it needs to go to
rather than to have four ships connect
them together and then connect them
to all
you need to and i think
we can just see from a size point of
view if you're building something like a
a mobile phone
fitting
one chip into it
even with the way that things have been
shrunk in technology now is much simpler
than trying to fit four ships
in there so is this this is a cost and
kind of miniaturization thing really
yeah so i mean the thing is so one
adventure is it reduces the cost because
you've only got one chip you need to
make that does
everything and so but it also makes it
easier to build the system because when
you've got circuits particularly when
they're running at the speeds that
they're running at now
you have to make sure that all the sort
of connections are
the same length otherwise the signals
can get out of phase with each other and
if you look at a modern motherboard you
can often see you get sort of like
weird patterns in the paths on the pcb
just to keep them all the same length so
that the signals arrive in phase with
each other at the same time so it makes
it much easier to design the system and
also there's a whole lot of things that
you suddenly no longer need
because for example the arm chip has the
signals coming off to it which needs to
drive the external bus
and that then connects to the memsi chip
which needs to receive those and pick
them back up and connect them in if
they're all on the same piece of silicon
you can sort of remove some of those
things and simplify the design because
you only have the connections to the
outside that you need this is probably
the simplest way you'd want to build a a
system on a chip and it combines the
main parts of the original machine down
to a single chip so that you can
actually sort of just simplify the
design of the motherboard you could
produce these much simpler and obviously
reduce your costs which is great but
obviously these days the functionality
that is being placed onto these systems
on ship is massively increasing um the
sort of designs in an iphone or other
mobile phone and an ipad on the m1 chip
and things they're not only including
the circuitry to do the computations the
graphics and so on they're also
including
video decompression and compression
engines including sort of hardware
encryption and decryption engines and
things that you need on there they're
adding functionality which traditionally
have been part of a separate things sort
of the digital signal processing and
image signal processing needed for a
camera and integrating onto the same
piece of silicon and the advantage of
that is that when you design your
system whether it's a computer a mobile
phone and things you no longer have to
think well okay i need to put
my cpu on there and then connect that to
the image signal processor chip and work
out how to run the connections there
i can just connect the camera directly
to the one system on a chip and that
system on chip can be connected possibly
it's even got the sort of the audio dax
built in there the analog side of things
so that can be connected directly to
your headphone output if you remember
them on a mobile phone
and things uh and
okay let's say the speaker on the mobile
phone for you when you're making a phone
call um if you remember them
and things and you can just simplify
everything so actually everything's
integrated into this one chip now the
advantage of that is it makes things
very very simple to build a phone you
have one chip a few power support
components on there and things and you
can put this together i'm talking at a
high level i'm not a chip designer
and things put that disclaimer in there
please sean
and stuff and it makes it easier to
design it but it also comes with a
disadvantage because
those things are always built in
if you've got separate things like here
and you only want the arm cpu
you can use just the arm cpu and put it
in a different design of machine is the
clock speed has increased i mean this is
this this run at eight megahertz this
one i think they managed to bump it up
to about 12 megahertz roughly getting
that much difference slightly faster
slightly slower
you didn't have to worry too much about
the design of your motherboard
signals from
electrical signals travel at some
function of the speed of light um three
times ten to the eight meters per second
they're going to travel
relatively quickly from one here when
your computer runs at eight megahertz as
your computer gets progressively faster
let's say we get to three gigahertz
where most machines sort of
are today
if you do the maths distance equal speed
times time the speed of light is three
times ten to the eight meters per second
the distance the time is one clock cycle
one over three times ten to the nine
cycles per second you start to think
well actually 10 centimeters is the
amount i can travel in one clock cycle
so if this sends out data at three
gigahertz
that's roughly 10 centimeters by the
time it's got here the cpus
on the next clock cycle either wanting
the data and things so it'll take at
least two clock cycles for the signal to
get from here and then back before you
take into account the processing time
that is involved because the computers
are running so fast and looking at those
tracks it could be double that distance
well exactly because i mean if you look
at it we're sort of coming along here
going around taking a sort of dog leg
around here sort of over the first
hurdle around the things jumping over
the waterfront
and finally we've got to the video
controller so actually of course you've
then got to go back
because if you want to
sort of respond to that you need to go
back and things uh and so actually
as your computer gets bigger you have to
either take that into account and design
the interconnect protocols the way that
they talk to each other
to be more like a network and say send
the data out and then you get it back
later
or you have to bring things closer
together and of course you bring things
closer together eventually you end up
with everything packaged together most
of this motherboard is empty space it's
just sort of literally there's nothing
on it on either side i think
whereas this one is densely packed
on both sides with interconnects between
the different chips on there of course
there are disadvantages as well to
system monitor in that you're you're
stuck with the integration you've got
when you design the system on a chip
which may be fine for a lot of devices i
mean if you look at apple they use their
chips in various different things the
the m1 chip is using the mac it's used
in the
ipad the a5 chip was used in the iphone
and in one of the apple tvs and things
they could reuse it
but often you think about well actually
the a5 chip probably had the image
signal processor
in there which was not being used on the
uh apple tv because it's got no camera
and things and so actually you're stuck
with that integration and that's fine if
it's got the things you want in there
but if it doesn't have the things you
want in there then it doesn't have it
you still have to put it as an external
device or live without it and things so
you can't
upgrade things in the same way you can't
say well actually i don't want a core i3
cpu in my system on a chip
and i want a z on that's a different
product line and so someone has to
design that and you have to put it in
there now it doesn't mean that it can't
be expandable you aren't forced to just
have what's in the system on the chip if
you design it you can put a pcie as an
output on there the raspberry pi 4
classically does that it has a pcie usb
chip on it usb 3 chip which talks to the
system on a chip to support the usb 3
ports and things and use the compute
module you can connect that up to
different things people have done
serial ata controllers nvme drives and
so on but
you the system on a chip is a fixed
functional piece that you get all or
nothing basically you can't pick and
choose to have part of it without
effectively
spinning up a separate chip but it does
make it much simpler to design a system
if the system on a chip does everything
you want it to
and bbc basic emerged as a compromise
between roger's experience of building
basics for earlier acorn machines and
the bbc's requirement for
a language which yeah i mean that's what
that's one way of thinking about it
filling up the whole screen 50 times a
second
and you have to generate everything
within those 312 and a half