Chapter 1B - Von Neumann Architecture-Building Blocks PDF

COMPUTER ORGANIZATION AND ARCHITECTURE CHAPTER 1B Von Neumann Architecture and Fundamental Building Block  Basic Organization of Von Neumann Machine  The Von Neumann Architecture THE PRINCIPLES : ▪ Data and instructions are both stored in the main memory. ▪ The conten...

COMPUTER ORGANIZATION AND ARCHITECTURE CHAPTER 1B Von Neumann Architecture and Fundamental Building Block  Basic Organization of Von Neumann Machine  The Von Neumann Architecture THE PRINCIPLES : ▪ Data and instructions are both stored in the main memory. ▪ The content of the memory is addressable by location. ▪ Instructions are executed sequentially, unless the order is explicitly modified.  The Von Neumann Architecture THE ARCHITECTURE : ▪ A central processing unit (CPU); it contains the control unit (CU), that coordinates the execution of instructions and the arithmetic/logic unit (ALU), which performs arithmetic and logic operations. ▪ Main memory. ▪ Von Neumann computers are general purpose computers. They can solve very different problems depending on the program they got to execute. The Von Neumann Architecture The Architecture The General-purpose (von Neumann) Architecture  The Von Neumann Architecture In the von Neumann architecture, a small set of circuits can be driven to perform very different tasks, depending on the software program, which is executed. ▪ The primary function of a CPU is to execute the instructions fetch from the main memory. ▪ An instruction tells the CPU to perform one of its basic operations. ▪ The CU is the one which interprets the instruction to be executed and which ‘tells’ the different other components of what to do. ▪ The CPU includes a set of registers, which are temporary storage devices typically used to hold intensively used data and intermediate result.  Von Neumann Architecture: Input Unit ▪ Input unit accepts coded information from human operators through electromechanical devices such as the keyboard or from other computers over digital communication lines. ▪ The information received is either stored in the memory for later reference or immediately used by the Arithmetic and Logic circuitry to perform the desired operation. ▪ Finally the result is sent back to the outside through the output unit.  Von Neumann Architecture: Input Unit ▪ The keyboard is wired so that whenever a key is pressed, the corresponding letter or digit is automatically translated into its corresponding code and sent directly to either the memory or the processor. ▪ Other kinds of input devices: Joy stick, track ball, mouse (pointing devices), scanner etc.  Von Neumann Architecture: Memory Unit ▪ The memory unit stores program and data. ▪ Primary memory (Main memory) ▪ Contains a large number of semiconductor cells each capable of storing one bit of information ▪ These cells are processed in group of fixed size called words containing ‘n’ bits. The main memory is organized such that the contents of one word can be stored or retrieved in one basic operation. ▪ For accessing data, a distinct address is associated with each word location  Von Neumann Architecture: Memory Unit ▪ Data and programs must be in the primary memory for execution. ▪ Number of bits in each word is called the word length and it may vary from 16 to 64 bits. ▪ Fast memory ▪ Expensive ▪ Time required to access one word is called Memory Access Time - 10nS to 100nS. This time is fixed and independent of the location. ▪ E.g. Random Access Memory (RAM)  Von Neumann Architecture: Memory Unit ▪ Secondary storage ▪ They are used when large amount of data have to be stored (also when frequent access is not necessary) ▪ E.g. Hard Disk, Compact Disk, Floppy Disk, Magnetic Tapes etc.  Von Neumann Architecture: Processor Unit ▪ The heart of the computer system is the Processor unit. ▪ Arithmetic and Logic Unit (ALU) ▪ Most computer operations (Arithmetical and logical) are executed in ALU of the processor. ▪ For example: Suppose two numbers (operands) located in the main memory are to be added. These operands are brought into arithmetic unit – actual addition is carried. The result is then stored in the memory or retained in the processor itself for immediate use.  Von Neumann Architecture: Processor Unit ▪ Note that all operands may not reside in the main memory. Processor contains a number of high speed storage elements called Registers, which may be used for temporary storage of frequently used operands. ▪ Each register can store one word of data. ▪ Access times to registers are 5 to 10 times faster than access time to memory.  Von Neumann Architecture: Processor Unit ▪ Control Unit ▪ The operations of all the units are coordinated by the control unit (act as the nerve centre that sends control signal to other units) ▪ Timing signal that governs the I/O transfers are generated by the Control Unit. ▪ Synchronization signals are also generated by the Control Unit ▪ By selecting, interpreting and executing the program instructions,the control unit is able to maintain order and direct the operation of the  Von Neumann Architecture: Processor Unit ▪ The control unit and ALU’s are usually many times faster than other devices connected to a computer system. ▪ This enabled a single processor to control a number of external devices such as video terminals, magnetic taped, disk memories, sensors, displays and mechanical controllers which are much slower than the processor  Von Neumann Architecture: Output Unit Output devices accept binary data from the computer -decodes it into original form and supplies this result to the outside world. E.g. Printer, Video terminals (provides both input & output functions), graphic displays, etc Processor Internal Organization ▪ Processor contains a number of registers used for temporary storage of data other than ALU and Control circuitry ▪ Instruction Register (IR) – holds the instruction that is currently being executed – its output is available to the control circuits which generate the timing signals that control the various processing elements involved in executing the instruction. ▪ Program Counter (PC) – During the execution of an instruction, the contents of the program counter are updated to hold the address of the next instruction to be executed. i.e. PC points to the next instruction that is to be fetched from the memory. Processor Internal Organization ▪ General Purpose Registers– Facilitates communication with the main memory. Access to data in these registers is much faster than to data stored in memory locations because the registers are inside the processor. ▪ Most modern computers have 8 to 32 general purpose registers. ▪ Memory Address Register (MAR) – holds the address of the location to or from which data are to be transferred ▪ Memory Data Register (MDR) – contains the data to be written into or read out of the address location. Processor Internal Organization Fundamental of Building Blocks  Counter ▪ A counter is a device which stores/displays the number of times a particular event/process has occurred. ▪ There are many types of counters. 2 types of counters are commonly used:  Up counters – increment in value  Down counter – decrement in value ▪ Counter circuits count in natural binary. Many types of counter circuits are available as digital building blocks.  Registers ▪ Registers are single, permanent storage location within a CPU used for a particular or defined purpose. ▪ It holds binary values temporarily either for storage, manipulation or calculation purposes. Registers are directly manipulated by the Control Unit (CU) during execution of instructions.  Programmable Logic Array (PLA) ▪ PLAs are general purpose logic devices that have the ability to perform a wide variety of specialized logic functions. A PLA contains a general purpose AND-OR-NOT array of logic gate circuits. ▪ The inputs to the AND gates in the array can be interconnected to perform a logic function. The process of connecting/disconnecting the inputs is known as programming. PLA circuit diagram  Register Transfer Notation ▪ The operations executed on data stored in registers are called microoperations. ▪ A microoperation is an elementary operation performed on the information stored in registers. For example shift, count, clear, and load. ▪ To specify the sequence of microoperations, symbols are used. This symbolic notation is called a Register Transfer Notation (RTN). ▪ Register Transfer Notation is a way of specifying the behavior of a digital synchronous circuit.  Register Transfer Notation Example: RTN: MAR IR means “The value from Instruction Register (IR) is copied into the Memory Address Register (MAR)”