[Music] well hello everyone welcome to this session and as promised in this particular lecture we are going to dive right into various classifications of computer architecture so without any further Ado let's get to learning now coming to computer architectures classifications there are various models among them we will be learning about two most popular approaches so let's start with the first one one computer architecture is broadly classified into specifically two categories V num architecture and non-von Numan architecture now one num machines have the following characteristics it has three basic Hardware subsystems the CPU the main memory and the io system moreover it must be a stored program computer that means the main memory system holds the program which controls the computer operation and the computer can manipulate its own program more or less also it can do the same to any other data stored inside the memory furthermore it carries out instructions sequentially so the CPU appears to execute one operation at a time well the major debate has always been about having a single path between the main memory and the processor proposed by this very architecture now already in our previous discussion we came to know about Von Newman's professorship at Princeton University and that is the reason why this architect ecture was also referred to as Princeton architecture now people from Harvard University proposed another model which adopted most of the features proposed in the Princeton architecture except for the fact they use two different memory units and thus Pioneer parallelism this is popularly known as Harvard architecture let's try to understand the need of it first of all systems having pure vum architectur stores the instructions and the data in the memory unit thus both the data and the instructions are faced over the same path this means the processor can't simultaneously read an instruction and operate on data this phenomenon is known as one num bottleneck and was first officially discussed by the great John beus inventor of beus normal form for context free languages during his 1977 ACM touring award lecture next there is modified Harvard architecture which cannot completely be classified as V Numan architecture as it doesn't strictly follow the V Numan principles but it is more of a combination between both the Harvard and the Princeton architecture now let's study them in a bit details now in Harvard architecture we have separate memory units one is for strictly storing the instructions and the other for the data items this way the processor can both read an instruction and perform data memory access at the same time therefore computers belonging to this architecture family are faster because instruction FES and data accesses are not competing for the single memory pathway anymore now coming to modified Harvard architecture it is very much like the Harvard architecture itself however it relaxes the strict division of instruction memory and data memory here the processor is accompanied by a small yet fast memory storage called cachi when the processor is executing from the cache it acts as a pure Harvard architecture and when it is accessing from the backing memory it acts like a pure V Numan machine this modification it widespread in modern processors so this was the first approach of classification of computer architecture let's move on to the next one in this model computer architectures are classified by a variety of characteristics including the number of processors the number of programs they can execute and the memory structures being used the the first group is s i SD that is single instruction stream single data stream the Von num architecture belongs to this specific category sisd computers have one CPU that executes one instructions at a time hence single instruction stream and FES and stores one item of data at a time hence single data stream the next group is simd that is single instruction stream multiple data stream processor array falls into this category simd machines have a control unit that operates like a vum machine that executes a single instruction stream but they have more than one alus the control unit generates the control signals for all the alus which execute the same operation on different set of data items generally in lock steps hence multiple data streams the next group of computers are MISD multiple instruction streams single data stream logically machine of this class would execute various different programs on the same data items this group doesn't have any particular practical implementation nonetheless some machines belonging to the next category can be used in this manner all right the next and the final type is mimd multiple instruction streams multiple data streams machines these are also known as multiprocessors these are comprised of more than one independent processors and each one of them can execute a different set of instructions hence multiple instruction streams on its own set of data hence multiple data streams now this classification was proposed by Michael J Flynn in 1966 since then it has been used as a tool in design of modern processors and and their functionalities that is why it is also known as Flynn's taxonomy all right folks that was the two most popular classifications of computer architecture hope you liked it and learned something new I'll see you guys in the next one thank you all for watching [Applause] [Music]