in this video we take a look at the differences between and the uses of sisk and risk processors [Music] so at the core of all computers is what is known as the instruction set this is effectively the set of all instructions written in machine code that can be recognized and executed by given processing unit or cpu there are two main different categories of instruction sets that you need to be aware of there's the complex instruction set computer sisk and the reduced instruction set computer risk so here on the screen is a high level abstraction of a storage design for a generic computer and it's going to serve the purpose of our illustration so important things to note we've got main memory at the top and it's got ten locations and they're addressed from zero zero zero zero in binary through to one zero zero one we also have what we're labeling the execution unit which is going to carry out all calculations now the execution unit can only operate on data that's been loaded into one of six registers and we've labeled them r zero zero 0 to r 1 0 1. so our task is to find the product of two numbers the first number is going to be stored in memory location zero zero zero zero the second number in zero zero zero one and then the result of the calculation the product of those two numbers should be stored back in memory location zero zero one zero so in a high level language this would be a line of code something like product equals num1 times num2 where each of those words are variables or locations so let's start with the complex instruction set computer so cis gains to complete the task in as few lines of assembly as possible now this means the processor hardware and the circuitry tends to be more complicated so it's able to understand and execute a series of operations the cisc processor could include a specific instruction for multiplying two numbers and we're going to call that malt here we've shown it on the screen when executed this instruction would load the two values into the register multiply them together and store the result back out so malt is an example in our abstraction here of a complex instruction it resembles the original command from the high-level language the compiler therefore is having to do very little work to translate the original high-level language statement into low-level assembly code however this complex instruction might take more than one machine or clock cycle in order to execute now we're going to come back to that point a bit later when we compare the two so although much less common today than it used to be the sisk architecture is mainly found in desktop computers and laptops intel's x86 processors still use the sys architecture although more recent changes beyond the scope of this course mean they operate very much like a risk fashion and they utilize micro code which allows them to leverage many of the benefits of the risk architecture which we're now going to look at so with risk processes the aim is to use simple instructions which will be executed within a single machine or clock cycle now in our generic computer example here that we're using at least we're going to say that the complex command such as malt doesn't exist we would need to separate it into a number of simpler commands in this situation we're going to need four lines of assembly two for loading the different contents of memory one for providing the product and another to store the result back out whereas remember before with the sisk architecture we had a single low-level command that performed all of that now there are more lines of code required in the assembly version than the high level version which only had one line this means the compiler is now being required to do much of the conversion work more ram is needed to store the assembly instructions so on the face of it it would seem that the risk architecture is much less efficient but we come back to the point that with this system each instruction can be completed in a single clock cycle these risk instructions require fewer transistors and less complex hardware this leaves more room for general purpose registers in cash and we already know the benefits of that at speeding up a processor from a previous video as all the instructions are uniform in terms of their execution time we can make use of pipelining another way of speeding up the processor we discussed earlier the use of risk processing results also in lower energy requirements risk architectures have become incredibly popular in low power and portable devices such as smart tvs thermostats smart watches phones tablets printers home assistants tb sticks and many many more as such arm processors and other architectures that work off of risk now make up well over 90 percent of all processors in use today so here is a summary of sisk architecture on the left compared to risk architecture on the right i'm not going to read it all to you but you might like to pause the video and take some notes so having watched this video you should be able to answer the following key question what are the differences between the risk and sisk architectures so that's everything covered in the specification so you can stop taking notes but if you're interested in learning a little bit more and going a little bit deeper then watch the remainder of this video so something not in the spec which is quite interesting to learn about is known as the performance equation now this is an equation commonly used for expressing a computer's performance potential now the sisk approach attempts to minimize the number of instructions per program but while sacrificing the number of cycles per instruction the risk philosophy does completely the opposite it attempts to reduce the cycles per instruction but at the cost of the number of instructions that end up in the end assembly program you can clearly see here some of the concepts that we've been talking about in raw numbers so look at the number of instructions available in sisk versus risk there are a lot more instructions in the complex instruction sets than the reduced instruction set varieties but you can see that there's a variable length of sisk instructions and of course this becomes problematic when we try to utilize pipelining to increase performance now risk gets around this by fixed sized instructions now even though risk-based processing has many advantages it did take well over a decade to gain acceptance on a large commercial scale risk lacks software support versus sisk especially in the early days windows 3.1 and 90 to 5 were designed with cisc processors in mind and most companies were unwilling to take a chance on risk which was seen as an emerging technology in the beginning intel cisc processors were a major setback for the emergence of risk intel had enormous influence and resources to throw at producing ever more powerful cis processes despite them becoming increasingly unwieldy and difficult to develop today though intel x86 is arguably the only chip that retains sisk architecture and even then if you dig a bit deeper below the surface you'll realize it implements many features such as micro codes that allows it to operate in a risk type fashion the reduction in price of ram and increased sophistication of compiler technology means the risk emphasis on software over hardware has become ideal you can easily see from this graph that sales of risk-based processors far outstrip intel sysversons which peaked at 0.3 billion processors back in 2011. you