CS 6290 I/O and Storage presents Storage Systems, Magnetic Disks, Trends for Magnetic Disks, Optical Disks, Magnetic Tapes, Using RAM for Storage, Busses for I/O, Buses in a System, Bus Design Decisions, CPU-Device Interface. | CS 6290 I/O and Storage Milos Prvulovic Storage Systems • I/O performance (bandwidth, latency) – Bandwidth improving, but not as fast as CPU – Latency improving very slowly – Consequently, by Amdahl’s Law: fraction of time spent on I/O increasing • Other factors just as important – Reliability, Availability, Dependability • Storage devices very diverse – Magnetic disks, tapes, CDs, DVDs, flash – Different advantages/disadvantages and uses Magnetic Disks Magnetic Disks • Good: cheap ($/MB), fairly reliable – Primary storage, memory swapping • Bad: Can only read/write an entire sector – Can not be directly addressed as main memory • Disk access time – Queuing delay • Wait until disk gets to do this operation – Seek time • Head moves to correct track – Rotational latency • Correct sector must get under the head – Data transfer time and controller time Trends for Magnetic Disks • Capacity: doubles in approx. one year • Average seek time – 5-12ms, very slow improvement • Average rotational latency (1/2 full rotation) – 5,000 RPM to 10,000 RPM to 15,000 RPM – Improves slowly, not easy (reliability, noise) • Data transfer rate – Improves at an OK rate •New interfaces, more data per .
