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[MUSIC]. 

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Let's take a look at our road map. 
We're at our first section that will 

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address the issues of data and 
addressing. 

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Namely, how do we store information in 
memory, how do we represent it in terms 

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of 0's and 1's. 
And how do we reference that data, in 

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other words, what addresses do we provide 
so we can find the data we've put in 

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memory again. 
So to before we get into that. 

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And the other topics in this section. 
We're going to start with a few 

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preliminaries about how we organize our 
hardware. 

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Lets take a look at this first picture 
that is a logical view of a modern 

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computing system. 
You'll notice that very prominently are 

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the CPU, the Central Processing Unit, and 
the memory. 

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There's a hide bandwidth channel between 
the memory and the CPU because the CPU 

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has to go to that memory to get all the 
data and instructions it will need in 

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order to know what to do and to what 
pieces data. 

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So that is going to be a very big focus 
of this course that connection is 

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actually going to be a little bit more 
complex than shown in this diagram. 

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There's going to be various levels of 
memory that we'll be looking at. 

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in addition, the CPU and memory are 
connected to a common bus that allows 

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data to flow between all the elements of 
a computer. 

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Some of the other elements are disks, 
which provide even more memory for us to 

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use. 
But are slower and little bit further 

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away from the CPU will also have a 
connection to the network. 

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So that we can get data over the internet 
we'll also have connections to peripheral 

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devices like mice and keyboards and 
cameras and those are often over a USB 

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interfaces. 
universal serial bus as well as others 

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that might be available depending on the 
computing, computing system you have. 

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Let's go a little deeper and look at a 
semi logical view. 

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In this case we're breaking things down a 
little bit, not only into a main CPU 

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shown here at the top. 
you'll notice that it's connected to a 

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bunch of memory on one side and maybe 
some specialized memory and processing 

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for graphics functions on the other. 
below it is another large chip that's 

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often common in most computers. 
And that's a IO controller, something 

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that really orchestrates that common buss 
that connects to all the other devices. 

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Some of those other devices might be the 
audio system the hard disc drives the USB 

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interfaces and so on. 
That are, make up the rest of the 

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computer. 
If we go yet a level deeper and go to the 

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physical view of the device. 
here we'll see a, a, a motherboard. 

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A board that includes all those major 
components of a computer. 

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Here in the center is the the CPU chip. 
it's surrounded by an IO chip, that 

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controls those peripherals connections 
for adding memory to the system. 

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And connections for hard disk drives to 
be connected to that common bus. 

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In addition, at the back of the machine, 
we'll typically see a whole bunch of 

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connections to those peripheral devices. 
Including audio components, mice, 

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keyboards and networks. 
If we focus then on the part that will be 

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most concerned with, namely the CPU and 
memory that we say at the top of our 

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first figure. 
We go a little deeper in and we'll see 

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that the CPU is composed of some things 
that hold data, we're going to call these 

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registers. 
And some things that hold instructions 

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and that will typically be called an 
instruction cache. 

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the thing that we need to understand at a 
very high level for now we'll get into a 

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lot more detail on this later but for now 
we need to understand that data. 

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Namely, the things we operate on are 
moved from memory to the registers. 

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That's where the CPU can actually have 
operations on that data. 

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And then, the results from those 
registers are moved back to memory. 

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This is done on the program control. 
In other words, we'll have specific 

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instructions to go get memory at a 
particular location in the memory and 

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bring it into a particular register. 
And similarly going in the other 

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direction from a specific register to a 
specific location in memory. 

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We'll also be getting instructions from 
memory into our instruction cache where 

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the CPU will find. 
The instructions to execute. 

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this is done under hardware control. 
In other words, the CPU has it's own 

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devices for getting that ins- next 
instruction. 

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And figure out whether it needs to go to 
the memory to find it, or if it already 

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has it in it's cache. 
why might it already have it in its 

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cache? 
Well if it's executing a loop for example 

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or a common procedure that had just 
recently executed, it might already be in 

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the cache. 
But that's done on the hardware control, 

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we don't worry about where to get the 
next instruction. 

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What we worry about in our programs is 
where to get the data, and where to put 

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the date once we've operated on it. 
We also want to talk about the 

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performance of our computing systems and 
performance is not just about CPU speed 

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mainly the clock rate the, the speed at 
which we connect to get one instruction 

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after another. 
Its also about getting those instructions 

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and the data they have to operate on from 
memory to the CPU. 

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That CPU memory bandwidth can limit 
performance. 

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And we have two common strategies for 
trying to improve that performance. 

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The first tries to make the memory wider. 
Namely we get more bits at once from the 

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memory. 
So, rather than getting. 

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one instruction at a time, we might get 
several instructions at a time, or not 

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one piece of data but several. 
Another, possibility is to move some of 

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the memory into the CPU itself, and 
actually have a smaller, but much faster 

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memory available to the CPU. 
This works particularly well when The 

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data and instructions are located near 
each other. 

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Or are a very small set of the all the 
possible locations in memory. 

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So, this memory in the CPU will be much 
smaller than the larger main memory. 

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We call this a cache, namely some place 
where we store our valuables. 

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nearby so that we can get to it easy. 
Now that we've talked about how our 

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computers are organized. 
we also have to talk about how we 

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represent those zeros and ones that we're 
going to be building all of our data and 

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instructions from. 
You'll notice that that bottom in this 

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slide, there's a figure that shows that, 
in fact, the 0 is represented by a low 

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voltage. 
A 1 represented by a high voltage. 

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And those can fluctuate a little bit. 
And it also takes a little bit of time to 

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go from a 0 to a 1 when we have some 
voltages that are intermediate. 

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We really don't want to be in this region 
because that can be confusing. 

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And that is in fact what limits the speed 
of our computing systems, how quickly we 

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can make these transitions between 0 and 
1 and 1 to 0. 

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So electronics are designed to make it 
easy to represent a value at this voltage 

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and a value at a low voltage and not 
worry about the values in between. 

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Rather, we restore our values as often as 
we can to these nicer voltages at the top 

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and bottom. 
How do we represent numbers? 

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Well here's a number in base 10 the 
number 351, that's the number of this 

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course here at UW. 
And this is in base 10 we're very 

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familiar with this number representation, 
we've seen it since elementary school. 

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the binary representation, of 351, is 
this number. 

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Now, how did I decide on how many 0's and 
1's to use? 

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Well, that was kind of arbitrary. 
In this, I could have also represented it 

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by the much shorter string of 1's and 0's 
that doesn't have that leading set of 

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0's. 
That would be the same thing as writing 

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351 base 10 or 0's, 0, 0, 351 base 10. 
You'll notice that we can always put 

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leading 0's in front of something that 
doesn't change the actual value. 

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So we'll have to decide how many bits we 
want to use to represent numbers. 

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And that's where we'll be going next.