Stuart Cunningham - Computer Platforms COMPUTER PLATFORMS Von Neumann Architecture & Terminology & Performance Week 3

Stuart Cunningham - Computer Platforms Week 3 CPU –Buses –Registers Von-Neumann Architecture –Fetch Execute Cycle –Von Neumann Model Memory –Types of memory Representing Information –Analogue & digital –Decimal, binary, hexadecimal Terminology & Performance –MIPS & Hertz –Bits ‘n’ bytes

Stuart Cunningham - Computer Platforms CPU Buses Parallel connections between low- level components of the computer –Size is measured by the number of parallel connections on the bus E.g.- 32-bit wide bus = 32 individual wires These bursts are called words A word is a set measure of bits (in this case we have a 32-bit word) Signals on buses follow strict timing sequences Some buses are bi-directional –Allowing two way flow of information

Stuart Cunningham - Computer Platforms CPU Registers Used to temporarily store data read from memory Registers are used to process instructions and data during the Fetch Execute Cycle –Two main types of register: Instruction Register (IR) –Commands to be performed Data Registers –Data upon which operations will be performed

Stuart Cunningham - Computer Platforms CPU Registers Common registers in the CPU: –Program Counter (PC) Holds the memory address of the next instruction to be executed –Memory Buffer Register (MBR) Briefly holds data and instructions that travel to and from memory Sometimes called MDR (Memory Data Register) –Memory Address Register (MAR) Holds the memory address locations of data and/or instructions to be read / written to memory –Current Instruction Register (CIR) Holds the instruction which is to be executed –General Purpose Registers ‘Working areas’ for data processed by the ALU

Stuart Cunningham - Computer Platforms Fetch Execute Cycle Defines how instructions are retrieved and carried out inside the processor (CPU) Sometimes called the Instruction Cycle or Automatic Sequence Control START Fetch next instruction from memory to CIR Increment PC Execute instruction in CIR STOP? END no yes

Stuart Cunningham - Computer Platforms Fetch Execute Cycle Fetch Stage –Copy contents of PC into MAR Value of PC presented via the address bus –Increment PC (point to next instruction) –Copy instruction from MBR into CIR via data bus START Fetch next instruction from memory to CIR Increment PC Execute instruction in CIR STOP? END no yes

Stuart Cunningham - Computer Platforms Fetch Execute Cycle Execute Stage –Decode instruction from CIR –Run instruction in CIR –Unless instruction is STOP, repeat cycle START Fetch next instruction from memory to CIR Increment PC Execute instruction in CIR STOP? END no yes

Stuart Cunningham - Computer Platforms Fetch Execute Cycle Instruction Set –The types of instruction that a particular machine can execute –The instructions that are carried out during the Fetch Execute Cycle –Types of instruction: Arithmetic and logical calculations on data Input and output of data Changing the sequence of program execution Transferring data between memory and CPU registers Transferring data between CPU registers –Instructions are split into two parts: Opcode (Operation Code)- the operation to be carried out Operand- The data upon which the operation should be performed

Stuart Cunningham - Computer Platforms Von Neumann Model Logical structure of the computer system

Stuart Cunningham - Computer Platforms Von Neumann Model Logically defines a complete computer system Centralised control of all processes of the computer system Defines main parts of the machine: –Memory Storage for instructions and data –Processing unit ALU functions –Control unit Interpreting instructions Issuing commands –Input and Output For entering and retrieving data

Stuart Cunningham - Computer Platforms Von Neumann Model Problem? –Von-Neumann Bottleneck –All instructions must be retrieved from memory before they are processed Memory (RAM) runs at slower speeds than the processor is capable of The difference between the speed of the RAM and the speed of the processor is the ‘bottleneck’ This is being remedied by faster RAM technologies –Such as SDRAM

Stuart Cunningham - Computer Platforms Memory (RAM) Many different types of RAM –SDRAM Synchronous DRAM Synchronises with processor buses –Max. approx 133 MHz Reasonably new –DDR SDRAM Double Data Rate SDRAM Transfers data on both sides of the clock cycle Effectively doubles transmission rate –EDO DRAM Extended Data Out DRAM –Gets the next block of memory while current block is being sent to the processor

Stuart Cunningham - Computer Platforms Memory (RAM) BEDO DRAM –Burst EDO RAM Only synchronise with CPU for short time –Processes four memory addresses in one go Only supports max. 66MHz processor buses FPRAM –Fast Page RAM –“Page Mode Memory” –Dynamic RAM –Allows faster access to adjacent memory locations Does not always store complete addresses NVRAM –Non Volatile RAM –Retains it’s contents when power is switched off –Powered by a battery –Or uses an EEPROM chip Electrically Erasable Programmable ROM Combination of SRAM and EEPROM chips –SRAM is an NVRAM derivative

Stuart Cunningham - Computer Platforms Video Memory (RAM) WRAM –Windows RAM Windows are large blocks of memory Supports two paths to transport data –Sends data for display as new information is being sent to the graphic adapter’s memory –Same principle as standard VRAM –Faster than VRAM because of Windowing SGRAM –Synchronous Graphic RAM Dynamic RAM Synchronise with processor buses up to 100 MHz Capable of opening two memory pages at once –Simulates dual data transmission of VRAM and WRAM Better than standard VRAM

Stuart Cunningham - Computer Platforms Analogue A continuously varying signal –Varying in terms of frequency, amplitude, or both A signal that is constantly changing Analogue can represent many values

Stuart Cunningham - Computer Platforms Digital A signal with discrete value changes Signal levels are either on or off Often thought of as either 1 or 0, especially in computers, but digital can represent many different values using discrete levels

Stuart Cunningham - Computer Platforms Decimal Base 10 Numbers we use in everyday life 10 values then increment to next digit –0, 1, 2, 3, 4, 5, 6, 7, 8, 9 –Each position represents a value of 10 to the positions power ‘Ten fingers & ten toes’ Decimal numbers –E.g

Stuart Cunningham - Computer Platforms Binary Base 2 Commonly used in computers to represent data 2 values, then increment next digit –0 or 1 –Each position represents a value of 2 to the positions power –On or off (Digital) Binary numbers –E.g

Stuart Cunningham - Computer Platforms Converting Decimal & Binary To convert decimal to binary: –If the decimal number is ODD, write a ‘1’ on the far right hand side –OR if the decimal number is EVEN, write a ‘0’ on the far right hand side –Divide the decimal number by TWO If there is a remainder then ignore it –If the number you have is ODD, write a ‘1’ to the left of the previous digit –OR if the number is EVEN, write a ‘0’ to the left of the previous digit –Repeat until your decimal number is 0

Stuart Cunningham - Computer Platforms Converting Decimal & Binary E.g.- –Decimal ’15’ = ODD = 1 –15/2 = 7.5 = 7 = ODD = 11 –7/2 = 3.5 = 3 = ODD = 111 –3/2 = 1.5 = 1 = ODD = 1111 Binary ‘1111’ = Decimal ’15’ !!!! We can ‘pad’ our binary number with 0’s –Eg: –Decimal ’32’ = EVEN = 0 –32/2 = 16 = EVEN = 00 –16/2 = 8 = EVEN = 000 –8/2 = 4 = EVEN = 0000 –4/2 = 2 = EVEN = –2/2 = 1 = ODD = Binary ‘100000’ = Decimal ’32’ !!!! We can ‘pad’ our binary number with 0’s –Eg:

Stuart Cunningham - Computer Platforms Converting Binary & Decimal To convert binary to decimal: –Write out the binary number –Add the positional values to each digit –Where there is a ‘1’ below the positional value highlight that positional value –Once all 1’s in the binary number have highlighted their positional values –Add all highlighted values together –Positional values: –These values can of course increase to the power of 2

Stuart Cunningham - Computer Platforms Converting Binary & Decimal E.g.- –Binary number: –Add positional values: – – –Highlight the positional values –Add the highlighted values together: = 27 So Binary = Decimal 27 !!

Stuart Cunningham - Computer Platforms Hexadecimal Base 16 Another common format for data representation –Easy to map against binary 16 values then increment next digit –0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F –Each position represents a value of 16 to the positions power Hexadecimal numbers –E.g FF FB 19 –Commonly notated with “0x” in front of values 0xFF or 0x53

Stuart Cunningham - Computer Platforms Hexadecimal Values ABCDEF ABCDEF DECIMALHEXADECIMAL

Stuart Cunningham - Computer Platforms Converting Decimal & Hexadecimal To convert decimal to hexadecimal: –Write out the decimal number –Write out the hexadecimal positional values –Find the largest hex positional value that your decimal number will divide into –Divide your decimal number by that hex positional value –Take the answer( ignore the remainder) and add it to the left hand side of your hex answer multiply this number by it’s positional value and then subtract it from your decimal number –Take what’s left of your decimal number and repeat the process until you have nothing left

Stuart Cunningham - Computer Platforms Converting Decimal & Hexadecimal E.g.- –Decimal 280 –Write Hex positional values –Divide 280 by 256 (=1) –Multiply 1 by 256 (=256) –Subtract 256 from 280 ( =24) –Divide 24 by 16(=1) –Multiply 1 by 16 (=16) –Subtract 16 from 24 (24-16=8) –Divide 8 by 1 (=8) –Write in the –Hex number = 118

Stuart Cunningham - Computer Platforms Converting Hexadecimal & Decimal To convert hexadecimal to decimal: –Write out the hexadecimal number –Add the positional values to each digit –Where there is a value greater than ‘0’ below the positional value highlight that positional value –Once all positional values have been highlighted, multiply the number below, by it’s positional value –Add all results of highlighted values together –Positional values: –These values can of course increase to the power of 16

Stuart Cunningham - Computer Platforms Converting Hexadecimal & Decimal E.g.- –Hex number 0x4C –Add positional values – – C –Highlight positional values –Multiply positional values by the number below 4*16 = 64 C*1 = 12*1 = 12 –Add these together 64+12=76

Stuart Cunningham - Computer Platforms MIPS & Hertz (Hz) MIPS = Millions of Instructions per Second –How many instructions a processor can carry out each second –Old form of measurement Inaccurate Some instructions take longer than others Hz = number of complete cycles per second MHz = Millions of cycles per second –In a processor a cycle is when the state of the control lines are changed

Stuart Cunningham - Computer Platforms Bits ‘n’ Bytes A bit is a single binary digit (1 or 0) A byte is eight bits –Four bits are sometimes called a nibble A kilobit (KB) is 1024 bits A kilobyte (Kb) is 1024 bytes A megabyte (Mb) is 1024 kilobytes A gigabyte (Gb) is 1024 megabytes A terabyte (Tb) is 1024 gigabytes

Stuart Cunningham - Computer Platforms What you know now (Week 3)… Von Neumann Architecture –Von Neumann Model –Buses –Registers –Fetch Execute Cycle –Memory Types of memory –SDRAM, EDO, FPRAM, EEPROM –WRAM, SGRAM –Digital & Analogue –Binary –Hexadecimal –Terminology