A-Level Computing#BristolMet Session Objectives#4 MUST describe the differences between the main types of primary memory SHOULD describe the function and purpose of the control unit, memory unit and ALU as individual parts of a computer COULD explain the use of registers in the functioning of the processor Create solutions to the Little Man Computer assignment

A-Level Computing#BristolMet Computer Processing STARTER: GO FOR Try to list 5 factors which affect how a computer performs. Ext: For each explain what affect it has and why. 1.Size of processor 2.Amount of Cache Memory 3.Number of cores4.Amount of RAM 5.Transfer speed of data buses. BONUS: Amount of free Hard Disk space...If a computer is using all or it’s RAM it will use a section of hard disk as a supplement. This is called VIRTUAL MEMORY. However this is still slower than pure RAM.

A-Level Computing#BristolMet Primary Storage This is also known as Main Memory or Primary Storage. INVESTIGATION (7 mins): Research what is known as the ‘bootstrap’ program of a computer. Take notes and prepare to explain where and how is stored in the computer and why it is so important. This is the first instructions the CPU receives when a computer is turned on and is commonly called the BIOS (Basic Input Output System). It contains code which controls the basic hardware settings of a PC. It is mainly stored in ROM (Read Only Memory) which is NOT erased when power is turned off.

A-Level Computing#BristolMet MEMEMORY – Remember?? To recap... There are 2 main categories of memory: RAM – Random Access Memory This is volatile memory as it’s erasable (without power) but can be accessed quickly by the CPU. ROM – Read Only Memory This is non volatile as the data Is retained without power. Therefore Knows how to start up (or boot) after Being turned off.

A-Level Computing#BristolMet 4 Min Investigation What type of memory is cache memory? Are there any sub-divisions of memory? Create a table and note their characteristics.

A-Level Computing#BristolMet Summary of Memory Use Speed of data transfer... TASK: Go shopping...Create a table and compare costs and quantities of secondary storage, RAM and CPU with cache memory. What are your conclusions?... TRANSFER SPEED INCREASES Secondary Storage CPU RAM Cache memory TYPECOSTQuantity Secondary Storage RAM CPU (with cache)

A-Level Computing#BristolMet The Fetch-Execute Cycle The CPU receives data and instructions in binary form. An instruction will have 2 parts – an instruction and possibly some data, a number or a memory location. The programs that the CPU needs to process are stored in main memory. The CPU simply fetches the next instruction it needs to process, decodes it and executes it before repeating the process. The speed of this cycle is determined by an electronic Real Time Clock (RTC) chip. The computer synchronises all processes to this clock signal. The clock speed is measured in Hertz (Hz) or cycles per second. TASK: 500 Hz would be 500 cycles per second, how many could a 3GHz processor be capable of? Fetch Decode Excecute

A-Level Computing#BristolMet Machine Code with The Little Man Computer Visit the following site and follow the simulations of the Fetch-Execute cycle using the Little Man Computer (LMC) This is an interpretation of how a processor handles machine code. The simulation shows instructions being excecuted. The Op Code (or Operation Code Field) is part of the binary code giving the instruction to be carried out i.e add or jump The Operand (Operand Field or address field) gives the address (memory location) where the data to be used in the operation can be found.

A-Level Computing#BristolMet Flow Chart Flow chart of solution to LMC Assignment 3

A-Level Computing#BristolMet Registers Registers keep a check on the progress of the instructions and data as it moves around the processor. Think of them as part of a logical operation rather than individual registers. Program Counter (PC) – In the CU. Counts the instructions as they are carried out and increments by (+1). Contains the address of the next instruction to be executed(Instructions are always stored in order) Memory Address Register (MAR) –stores the address of the memory location currently in use, sent by the PC. Memory Data Register (MDR) – A copy of the instruction held in the MAR is stored here so that the memory unit and processor and work on it at the same time. Current Instruction Register (CIR) – the instruction now in the MDR is copied into the CIR. In here it can be spilt into 2 parts; 1 part is sent to be decoded so that the processor knows what the instruction is (and signals can be sent to other parts of the processor which may be required to carry out the instruction). The other part is an address stating whereabouts in the memory the required data is.

A-Level Computing#BristolMet Registers CIR continued... E.G if an instruction of ADD 20 is given it will be split into: ADD – ALU works out how to do an add 20 – is where the data to be added will be found (the address) The address will be sent back to the MAR Memmory will be searched and whatever is address ‘20’ will be copied into the MDR. The value in the MDR can then be used as per instructed by the CIR i.e Adding As the instruction is arithmetic it will be sent to the Accumulator (a special storage register with the ALU) to be carried out

A-Level Computing#BristolMet More on Buses The signals being sent around the processor are again called buses. 3 buses you need to remember are: The Control Bus – The CU uses this to send commands to different parts of the processor. The Data Bus – carries data from one register to another. The Address Bus – carries the location address to which the data is going.