Software Design and Development Computer Architecture Computing Science

Learning Objectives By the end of this topic you will be able to: describe the function of the registers, the arithmetic and logic unit and the control unit in a processor; describe the function of the registers, the arithmetic and logic unit and the control unit in a processor; describe the role of the control, address and data buses in the fetch execute cycle; describe the role of the control, address and data buses in the fetch execute cycle; describe how cache memory affects processor performance; describe how cache memory affects processor performance describe modern trends in computer architecture;

Learning Objectives By the end of this topic you will be able to: understand what an emulator is and how it is used; describe the concept of a virtual machine; understand the influence that mobile devices have on the software development process. understand the influence that mobile devices have on the software development process.

Processor components Processors have three main components Arithmetic and Logic Unit (ALU) Control; Unit Registers

Processor components The Arithmetic and Logic Unit performs calculations The Control Unit loads, decodes and executes instructions The Registers are small memory locations used by the processor

Buses Buses are the lines which connect the CPU to the main memory There are three buses – Data bus – Address bus – Control bus

Links between Processor and memory Address Bus Data Bus Control Bus Processor Memory

Registers Registers are temporary storage areas in the processor which can be used to hold: – The address of the next instruction (Program Counter) – The address where data is to be read from or written to (Address Register) – The result of the last calculation (Accumulator) – Data or instructions transferred between the CPU and memory (Data Register) – The current instruction being decoded (Instruction Register)

Registers Arithmetic and Logic Unit Control Unit Accumulator Instruction register Program Counter Address register Data register Memory Control linesAddress BusData Bus

The Address Bus: The address bus is a 1 way bus 1.The processor sets up the address register with the address of the memory location to be accessed 2.The processor activates the read or write line on the control bus 3.Data is then transferred to or from the data register via the data bus

The Data Bus Memory Read / write Operation The data bus is a 2 way bus The memory location to be read from or written to is set up with the address bus The read or write line is activated on the control bus The data is transferred to or from the data register via the data bus

Read Operation Address Bus Data Bus Control Bus Processor Memory Read line Data RegisterAddress Register Control Unit Program Counter

Read Operation Address Bus Data Bus Control Bus Processor Memory Read line Data RegisterAddress Register Control Unit Program Counter

Read Operation Address Bus Data Bus Control Bus Processor Memory Read line Data RegisterAddress Register Control Unit Program Counter

Read Operation Address Bus Data Bus Control Bus Processor Memory Read line Data RegisterAddress Register Control Unit Program Counter

Write Operation Processor Memory Write line Address BusControl Bus Data RegisterAddress Register Control Unit Data Bus Program Counter

Write Operation Processor Memory Write line Address BusControl Bus Data RegisterAddress Register Control Unit Data Bus Program Counter

Write Operation Processor Memory Write line Address BusControl Bus Data RegisterAddress Register Control Unit Data Bus Program Counter

Write Operation Processor Memory Write line Address BusControl Bus Data RegisterAddress Register Control Unit Data Bus Program Counter

The Fetch - Execute cycle Fetch Instruction Decode Instruction Execute Instruction

The Fetch - Execute cycle in detail Transfer Program Counter (PC) to Memory Address Register (MAR) Increment the Program Counter Activate Read line (via Control bus) Transfer instruction to Data Register (via Data bus) and then to Control Unit Decode Instruction Execute Instruction

The contents of the Program Counter are copied into the Address Register Address Bus Data Bus Control Bus Processor Memory Read line Data RegisterAddress Register Control Unit Program Counter Instruction Register

The Program Counter is incremented Processor Memory Write line Address BusControl Bus Data RegisterAddress Register Control Unit Data Bus Program Counter

Instruction Register The read line is activated and the contents of memory at the location are copied into the Data Register Address Bus Data Bus Control Bus Processor Memory Read line Data RegisterAddress Register Control Unit Program Counter

Instruction Register The Contents of the Data Register are copied into the Instruction Register Processor Memory Write line Address BusControl Bus Data RegisterAddress Register Control Unit Data Bus Program Counter

The Instruction is decoded Processor Memory Write line Address BusControl Bus Data RegisterAddress Register Control Unit Data Bus Program Counter Instruction Register

The Instruction is executed Processor Memory Write line Address BusControl Bus Data RegisterAddress Register Control Unit Data Bus Program Counter Instruction Register

Cache memory Cache memory is memory that can be accessed more quickly than regular RAM. Copies of instructions and data that are frequently used are stored here Processor will try to predict which instructions are needed and load them into cache

Cache memory Accessing cache memory is quicker because It uses faster (and more expensive) memory chips It is closer to the processor than normal RAM

Cache memory Cache memory comes in different levels Level 1 (L1) cache, which is extremely fast but relatively small, is located close to the processor. Level 2 (L2) cache is located half-way between the process and the system bus; it is fairly fast and medium-sized. Level 3 (L3) cache is relatively large and close to RAM.

Modern trends in architecture Strategies used to improve processor performance Speeding up the processor Increasing the instruction size executed in one operation Reducing the size of the transistors

Modern trends in architecture Increasing on-chip memory Parallel computing Possible developments in future Quantum computing Optical computing

Emulators An Emulator is a piece of software that allows a computer system to emulate another computer system. They can be used for several purposes. For example To allow programs written for obsolete machine to run on a modern system. This is often to allow computer games written for consoles or arcade systems to run on modern machines

Emulators A second reason is to allow the development of software for systems that have not yet been built. This allows software for a new system to be available when the system is first launched. Virtual machines are also examples of emulators

Virtual machines Virtual machines are again pieces of software that allow multiple types of software to run on a single machine. They can be used to allow several OS to run on a single machine, or several copies of the same OS to run on one machine. They can also be used to provide program portability. A single version of a program can be created and then a virtual machine created for each OS that it has to run with. This is the process that programs written in Java use with the Java Virtual Machine.

Mobile devices Rise in use of mobile devices has led to Need for emulators for development of software Redesign of displays for smaller screen sizes Need for touch screen technology Dealing with more limited bandwith Integrating facilities like GPS