okay welcome back everybody this is the first video and for the third topic the topic being hardware to support the igcse computer science um from cambridge we'll be covering the um central processing unit the cpu the microprocessor and we'll be looking at von neumann architecture in general we will also look at the logic unit the alu and the control unit and some of the registers these are things inside of the cpu and we'll look at the control bus the address bus and the data bus this is part one of computer architecture we will then move on and finish this um in video two okay the topic is hardware um hardware everything that is sort of tangible physical on your computer from the actual base unit itself be it a laptop or a desktop computer the monitor input devices sensors barcode readers your keyboard and your mouse of course um output devices speakers headphones projectors laser printers inkjet printers 3d printers to the things that are actually inside of the computer such as the computer memory the computer storage and then external storage um that can be sort of added to at a later date so that's computer hardware we're going to focus though on this thing the cpu the brains of the computer so here we go the central processing unit or the cpu as it's known also known as a microprocessor or a processor is central to all modern computer systems including your tablets such as an ipad and your smartphones cpu is very often installed as an integrated circuit on a single microchip the cpu has the responsibility for the execution or processing of all the instructions and data in a computer application it basically controls the input devices the output devices the storage the memory gets them all talking to each other and gets your computer doing specific jobs it is the brains it's the central processing it's the brains of the computer so let's have a little look at the history behind computers and the chap called von neumann and von neumann architecture early computers as you can see here so from the turn of the 1940s other computers were fed data while the machines were actually running it wasn't possible to stop programs or data which meant they couldn't operate without considerable human interaction here's some guys getting ready to feed off looking at the results from this great big silly sized computer in the mid 40s john von neumann developed a concept of the stored program computer the um stored program computer has been sort of the model for um all computers ever since so here we go the von neumann architecture has the following main features the concept of the central processing unit okay the cpu was able to access the memory directly the computer memory could store programs as well as data and stored programs were made up of instructions which could be executed in a sequential order a program basically so what is inside the cpu obviously it's the brains of the computer it's a central processing unit but what's inside it was made up of sort of three distinct areas okay we've got first of all the control unit then we've got the alu the arithmetic and logic unit and then we've got a series of registers okay also and you'll be familiar with this there is a system clock okay um this basically controls everything it's like like a like a timer which synchronizes um all the components it keeps them in time okay without this um the computer would simply not work the frequency of the pulses is known as the clock speed clock speed is measured in hertz the higher the frequency the more instructions can be performed in any one given moment in the 1980s a little bit of history again processors commonly run at a rate of between three megahertz or um to five megahertz three million to five million pulses or cycles per second now in today's processes um these commonly run at anything between um three gigahertz um to five gigahertz which is like five million to five billion pulses or cycles per second so you can see there's quite a jump from the 1980s to present day so 40 years on i just want to talk a little bit about what the computer is doing in terms of um where it's getting its information from so that the cpu takes data from programs held on the hard disk this thing here and puts them into the ram temporarily so i want to run something from microsoft word so i'm going to find the program that i've been working on on the hard disk i'm going to load it into the ram so i can work on it this is done because read write operations carried out using the ram are considerably faster than read write operations to the to the hard disk to the backing store consequently any key data needed by an application will be stored temporarily in rhyme to considerably speed up the operations so let's have a little talk about each of these um each of these things starting with the control unit the control unit reads an instruction from memory the address of the location where the instruction can be found is stored in the um pc yeah the program counter register this instruction is then interpreted using the fetch decode execute cycle which we'll be covering in the second video during that process sync signals are generated along the control bus to tell the other components in the computer what to do the control unit ensures synchronization of data flow and program instructions throughout the computer controlling everything the control unit the next thing is the arithmetic and logic unit as the name sort of suggests this is used for mathematical calculations it allows the required arithmetic or logic basically pluses and minuses and shifting for multiplication and division and the and and the or basically the gate operations to be carried out whilst a program is being run it is possible for a computer to have more than one alu to carry out specific functions as i just said multiplication and division are carried out by a sequence of addition subtraction and left or right shifts we have covered this in chapter one okay please refer to one of those videos if you want to talk a little bit more see a little bit more about shifting okay up and down registers and finally the registers we've got the mar the memory address register the mdr the um and finally registers we've got these four registers here which we'll talk about a little bit later but there's um a small amount of high speed memory and these contained again within the cpu they're used by the process to store small amounts of data that are needed during processing such as the address of the next instruction to be executed the current instruction being decoded and the results of calculations okay and here's a little bit more of a breakdown of what these things do so we have the current instruction register the cir we've got the accumulator the acc the memory address register mar memory data or the buffer register the mdr and the program counter and you can see what all of these do here okay moving on how does the cpu talk to the memory and how does it talk to the input and output devices well we use a thing called a series of things called buses three main types of buses the control bus the address bus and the data bus so but what do they do well the address bus carries memory addresses from the processor to other components such as primary memory and input and output devices the control bus carries control signals from the processors to other components the control bus also carries the clocks pulses and finally the data bus this carries the actual data between the processor and other components okay so those three buses are carrying data carrying information between the memory the cpu and the input and output rather the ports to the input and output devices we'll talk a little bit about memory about where things live on in memory basically memory is made up of two partitions the address where something lives and the content basically the the information of the data so the data and where it lives each partition consists of an address and its contents the table shown uses eight bits for each address okay eight bits and a bits for the content in a real computer of course the address and its contents are actually much much larger than this the address will uniquely identify every location in the memory and the contents were will be the binary values stored in each location okay so let's talk about how information is retrieved and used from ram in accordance with this the registers on this on the cpu so two examples the um of how the mar and the mdr registers can be used when carrying out a read and write operation um to and from the memory first consider the read operation what we will here we go we've got we've got a little address and content on the on the memory here from the ram okay suppose we want to read the contents of the memory location yeah the two registers are used as follows well let's have a little look first of all the address of location 111 zero zero zero one to be read from a list written into the mar so it writes this address into the mar a read signal is sent to the computer's memory the contents of this memory or location and then put into the mdr what is stored in this well it's this data here so two registers the data and the address okay now let's consider the right operation again we will use memory section shown in this table here this particular section here the one in orange the data to be stored is first written into the mdr the memory data register okay as you can see here we've put the data from here and we've put it into the mdr so the content and the address on the on ram yeah ram memory we've written it to the mdr on the cpu this data is to be written into a location address here so this is this address is now written into the mar okay so we've put the address into the mar finally a write signal is sent to the computer memory and the value yep this one here will then be written into the correct memory location so that is it for memory and that is um basically ram talking to the two registers the mdr and the mar on the cpu that is it for this first lesson as i said before we will move on to the fetch decode and execute cycle and finish off this this first part computer architecture okay thank you very much for watching please please subscribe if you haven't done so already and i will see you very very soon thank you very much indeed