ddr memory-基本工作原理分析.pptVIP

Memory Optimizations Memory Technology Some optimizations: Synchronous DRAM Added clock to DRAM interface Burst mode with critical word first Wider interfaces 4 bit transfer mode originally In 2010, upto 16-bit busses Double data rate (DDR) Transfer data on both rising and falling edge Memory Optimizations Memory Optimizations DDR: DDR2 Lower power (2.5 V - 1.8 V) Higher clock rates (266 MHz, 333 MHz, 400 MHz) DDR3 1.5 V 800 MHz DDR4 (scheduled for production in 2014) 1-1.2 V 1600 MHz GDDR5 is graphics memory based on DDR3 Memory Optimizations Graphics memory: Achieve 2-5 X bandwidth per DRAM vs. DDR3 Wider interfaces (32 vs. 16 bit) Higher clock rate Possible because they are attached via soldering instead of socketted Dual Inline Memory Modules (DIMM) Reducing power in SDRAMs: Lower voltage Low power mode (ignores clock, continues to refresh) Virtual Machines First developed in 1960s Regained popularity recently Need for isolation and security in modern systems Failures in security and reliability of standard operation systems Sharing of single computer among many unrelated users (datacenter, cloud) Dramatic increase in raw speed of processors Overhead of VMs now more acceptable Virtual Machines Emulation methods that provide a standard software interface IBM VM/370, VMware, ESX Server, Xen Create the illusion of having an entire computer to yourself including a copy of the OS Allows different ISAs and operating systems to be presented to user programs “System Virtual Machines” SVM software is called “virtual machine monitor” or “hypervisor” Individual virtual machines run under the monitor are called “guest VMs” Impact of VMs on Virtual Memory Each guest OS maintains its own set of page tables VMM adds a level of memory between physical and virtual memory called “real memory” VMM maintains shadow page table that maps guest virtual addresses to physical addresses Requires VMM to detect guest’s changes to its own page table Occurs naturally if accessing the page