Physical Memory and Physical Addressing ( Chapter 10 )Memory TechnologiesRAMSlide 4Measures of Memory TechnologyDensitySpeedLatencyMemory ControllerSteps to Process Memory RequestRead and Write Cycle TimeSDRAM and SSRAMMultiple Data Rate Memory TechnologiesMemory OrganizationInternal Hardware StructureMemory Transfer SizePhysical AddressesPhysical Memory OperationsByte Addressing With Word TransfersTranslation of AddressesPhysical Address NumberMemory Banks and InterleavingPhysical Memory and Physical Addressing( Chapter 10 )byPolina ZapreyevaMemory TechnologiesRAMSRAM DRAMcircuit for one bitwrite enableinput outputcircuit for one bitwrite enableinput outputrefreshRAMRAMStatic RAMStatic RAMsimple internal structurecircuits of multiple transistorshigh speedno need to refresh informationtakes more space (lower density)high power consumptiongenerates a lot of heatvery expansiveDynamic RAMDynamic RAMconfusing internal structurecapacitor-like circuitlower speedneeds to be constantly rewrittentakes less space (higher density)low power consumptionless heat generatedcheapMeasures of Memory TechnologyDensityLatencyCycle timesDensityDensityDensity = number of bits/ standard size chipHigher densityHigher densityAdvantages: more memory in same physical spaceDisadvantages: high power consumption and great amount of heatSpeeedSpeed is how fast the memory responds to request Performance of read (access) and write (update) operations should be considered separately.LatencyLatencyLatency is the time it takes to complete an operation.This is not the best measure of memory technology because it doesn’t provide complete information.MemoryMemory ControllerController Processor, or any other device, accesses physical memory through a hardware known as memory controller that provides an interface.ProcessorMemory ControllerPhysical MemorySteps to Process Memory RequestSteps to Process Memory Requestdevice presents a read or write requestcontroller translates that for the memoryand passes the signal for memory chipscontroller returns an answercontroller resets hardware circuits for next operationRead and Write Cycle TimeRead and Write Cycle TimeLatency doesn’t count the time that controller uses to reset its circuits. A better measure of performance is cycle time.Read cycle time and write cycle time measure how quickly the memory system handles successive requests.SDRAM and SSRAMSDRAM and SSRAMClock cycles of the processor and memory may differ. Memory controller handles this problem, but this results in delay.This problem had been fixed by synchronizing the two clocks. This resulted in two technologies: SDRAM (synchronized DRAM) and SSRAM (synchronized SRAM)Multiple Data Rate Memory TechnologiesFast Data Rate Memories:-Double Data Rate-Quadruple Data RateMemory OrganizationInternal Hardware StructureMemory bus (bus) is the hardware connection between a processor and memory.processor controllerphysical memory...parallel interfaceMemory Transfer SizeMemory transfer size isamount of data that can be read or written in a single operation. Also called word size orword width. Word is a block of memory with number of bits equal to memory transfer size.Note: Word size defines the size of standard integer and single-precision floating point.Physical AddressesWord Addressingeach word of memory is assigned a unique physical memory addresshigher performancereads or writes entire wordByte Addressingeach byte of memory is assigned a unique physical memory addresslower performancereads or writes single bytecontroller must support byte transferPhysical Memory OperationsThe controller for physical memory always always accepts or delivers entire wordaccepts or delivers entire word; hardware does not provide a way to read or write less than a complete word.When reading provides and address, when writing an address and data.Byte Addressing With Word TransfersTo read a single byte: -convert byte address to word address-read word-extract desired byteTo write a single byte:- convert byte address to word address- read word-replace desired byte-write entire word backTranslation of AddressesMathematically:word address = byte address/ word size(ignore the reminder)byte offset = byte address (mod (word size))Physical Address NumberNo computation required:Byte Addressoffsetword addressMemory Banks and InterleavingMemory bank is a memory unit with own controller; application parallelism to increase performance. Can be controlled by the user.Interleaving spreading consecutive bytes of memory across separate memory modules. Often done automatically
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