Chapters 8 9 partial coverage 1 2004 Morgan Kaufmann Publishers Interfacing Processors and Peripherals I O Design affected by many factors expandability resilience Performance access latency throughput connection between devices and the system the memory hierarchy the operating system A variety of different users e g banks supercomputers engineers Interrupts Processor Cache Memory I O bus Main memory I O controller Disk Disk I O controller I O controller Graphics output Network 2 2004 Morgan Kaufmann Publishers I O Important but neglected The difficulties in assessing and designing I O systems have often relegated I O to second class status courses in every aspect of computing from programming to computer architecture often ignore I O or give it scanty coverage textbooks leave the subject to near the end making it easier for students and instructors to skip it GUILTY we won t be looking at I O in much detail be sure and read Chapter 8 in its entirety you should probably take a networking and or storage class 3 2004 Morgan Kaufmann Publishers I O Devices Very diverse devices behavior i e input vs output partner who is at the other end data rate 4 2004 Morgan Kaufmann Publishers I O Example Disk Drives Platters Tracks Platter Sectors Track To access data seek position head over the proper track 3 to 14 ms avg rotational latency wait for desired sector 5K 15K RPM transfer grab the data one or more sectors 30 to 80 MB sec 5 2004 Morgan Kaufmann Publishers I O Example Buses Shared communication link one or more wires Difficult design may be bottleneck length of the bus number of devices tradeoffs buffers for higher bandwidth increases latency support for many different devices cost Types of buses processor memory short high speed custom design backplane high speed often standardized e g PCI I O lengthy different devices e g USB Firewire Synchronous vs Asynchronous use a clock and a synchronous protocol fast and small but every device must operate at same rate and clock skew requires the bus to be short don t use a clock and instead use handshaking 6 2004 Morgan Kaufmann Publishers I O Bus Standards Today we have two dominant bus standards 7 2004 Morgan Kaufmann Publishers Other important issues Bus Arbitration daisy chain arbitration not very fair centralized arbitration requires an arbiter e g PCI collision detection e g Ethernet Operating system polling interrupts direct memory access DMA Performance Analysis techniques queuing theory simulation analysis i e find the weakest link see I O System Design Many new developments 8 2004 Morgan Kaufmann Publishers Pentium 4 I O Options Pentium 4 processor DDR 400 3 2 GB sec Main memory DIMMs DDR 400 3 2 GB sec System bus 800 MHz 604 GB sec AGP 8X Memory 2 1 GB sec Graphics controller output hub CSA north bridge 0 266 GB sec 1 Gbit Ethernet 82875P Serial ATA 150 MB sec 266 MB sec Parallel ATA 100 MB sec Serial ATA 150 MB sec Parallel ATA 100 MB sec Disk Disk Stereo surroundsound AC 97 1 MB sec USB 2 0 60 MB sec I O controller hub south bridge 82801EB 20 MB sec CD DVD Tape 10 100 Mbit Ethernet PCI bus 132 MB sec 9 2004 Morgan Kaufmann Publishers Fallacies and Pitfalls Fallacy the rated mean time to failure of disks is 1 200 000 hours so disks practically never fail Fallacy magnetic disk storage is on its last legs will be replaced Fallacy A 100 MB sec bus can transfer 100 MB sec Pitfall Moving functions from the CPU to the I O processor expecting to improve performance without analysis 10 2004 Morgan Kaufmann Publishers Multiprocessors Idea create powerful computers by connecting many smaller ones good news works for timesharing better than supercomputer bad news its really hard to write good concurrent programs many commercial failures Processor Processor Processor Cache Cache Cache Processor Processor Processor Cache Cache Cache Memory Memory Memory Single bus Memory I O Network 11 2004 Morgan Kaufmann Publishers Questions How do parallel processors share data single address space SMP vs NUMA message passing How do parallel processors coordinate synchronization locks semaphores built into send receive primitives operating system protocols How are they implemented connected by a single bus connected by a network 12 2004 Morgan Kaufmann Publishers Supercomputers Plot of top 500 supercomputer sites over a decade Single Instruction multiple data SIMD 500 Cluster network of workstations 400 Cluster network of SMPs 300 Massively parallel processors MPPs 200 100 0 93 93 94 94 95 95 96 96 97 97 98 98 99 99 00 Sharedmemory multiprocessors SMPs Uniprocessors 13 2004 Morgan Kaufmann Publishers Using multiple processors an old idea Some SIMD designs Costs for the the Illiac IV escalated from 8 million in 1966 to 32 million in 1972 despite completion of only of the machine It took three more years before it was operational For better or worse computer architects are not easily discouraged Lots of interesting designs and ideas lots of failures few successes 14 2004 Morgan Kaufmann Publishers Topologies P0 P1 P2 a 2 D grid or mesh of 16 nodes P3 P0 P4 P1 P5 P2 P6 P3 P7 P4 P5 P6 P7 b Omega network a Crossbar b n cube tree of 8 nodes 8 23 so n 3 15 2004 Morgan Kaufmann Publishers Clusters Constructed from whole computers Independent scalable networks Strengths Many applications amenable to loosely coupled machines Exploit local area networks Cost effective Easy to expand Weaknesses Administration costs not necessarily lower Connected using I O bus Highly available due to separation of memories In theory we should be able to do better 16 2004 Morgan Kaufmann Publishers Google Serve an average of 1000 queries per second Google uses 6 000 processors and 12 000 disks Two sites in silicon valley two in Virginia Each site connected to internet using OC48 2488 Mbit sec Reliability On an average day 20 machines need rebooted software error 2 of the machines replaced each year In some sense simple ideas well executed Better and cheaper than other approaches involving increased complexity 17 2004 Morgan Kaufmann Publishers Concluding Remarks Evolution vs Revolution More often the expense of innovation comes from being too disruptive to computer users Acceptance of hardware ideas requires acceptance by software people therefore hardware people should learn about software And if software people want good machines they must learn more about hardware to be able to communicate with and thereby influence hardware engineers 18 2004 Morgan Kaufmann Publishers