Disk Storage Systems-Advance Computer Architecture-Lecture Slides, Slides of Advanced Computer Architecture

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Today’s Topics Recap: Disk Storage Systems Interfacing Storage Devices Conclusion docsity.com Recap: Multiprocessing In last four lectures we discussed how the computer performance can be improved by Parallel Architectures Parallel Architecture is a collection of processing elements that cooperate and communicate to solve larger problems fast Parallel architectures are implemented as: SIMD, MISD and MIMD machines, where the MIMD machines facilitate complete parallel processing docsity.com Today the :  Processing Power doubles every 18 months  Memory Size doubles every 18 months; and  Disk positioning rate (Seek + Rotate) doubles every 10 Years Recall the 2nd lecture, where we discussed the quantitative principles to define the computer performance, we noticed that the execution time of CPU is not the only measure of computer performance Recap: outside processor docsity.com The overall performance of a computer is measured by its throughput, which is very much influenced by the systems external to the processor As we have already pointed out in 25th lecture that measuring the overall performance of a powerful Uni-processor or a parallel processing architecture without considering the I/O devices and their interconnection, is just like trying to determine the road performance of a car, which is fitted with powerful engine but is without wheels Introduction: outside the processor docsity.com The effect of neglecting the I/Os on the overall performance of a computer system can best be visualized by Amdahl's Law which identifies that: system speed-up limited by the slowest part! Let us consider computer whose response time is 10% longer than the CPU time If the CPU time is speeded up by a factor of 10 then neglecting the I/Os, the overall speed up as determined using the Amdahl's Law is 5; i.e., Introduction: outside the processor docsity.com I/O System Processor Cache Memory - I/O Bus Main Memory I/O Controller Disk Disk I/O Controller I/O Controller Graphics Network interrupts An I/O system comprises storage I/Os and Communication I/Os docsity.com I/O Systems The Storage I/Os consist of Secondary and Tertiary Storage Devices; and The communication I/O consists of I/O Bus system which interconnect the microprocessor and memory with the I/O devices Today we will talk about the storage I/O The secondary and tertiary storages include: magnetic disk, magnetic tape automated tape libraries, CDs, and DVDs These devices offer bulk data storage, but on the contrary are too large for embedded applications docsity.com Disk Storages: Technology Trends As you can see from the plot shown here that extensive improvement have been made in the disk capacity; before 1990 disk capacity doubled every 36 months; and now every 18 months; docsity.com Historical Perspective 1956 - early 1970s – IBM Ramac and Winchester were developed for mainframe computers as proprietary interfaces – Steady shrink in form factor: 27 in. to 14 in. 1970s developments – 5.25 inch floppy disk form-factor (microcode into mainframe) – early emergence of industry standard disk interfaces ST506, SASI, SMD, ESDI docsity.com Disk History  Capacity of Unit Shown Megabytes; and  Data density: M bit/sq. in. 1973: Capacity: 140 MBytes Density: 1. 7 Mbit/sq. in 1979: 2,300 MBytes 7. 7 Mbit/sq. in docsity.com Historical Perspective Early 1980s: era of PCs and first generation workstations; and Mid 1980s: era of Client/server computing and Centralized storage on file server This voyage of computing from first generation to client/server resulted in end of proprietary interfaces and: Accelerated disk downsizing: 8 inch to 5.25 inch Mass market disk drives become a reality industry standards: SCSI, IPI, IDE 5.25 inch drives for standalone PCs, docsity.com DRAM as % of Disk over time MBits per square inch: 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 1974 1980 1986 1992 1998 470 v. 3000 Mb/si 9 v. 22 Mb/si 0.2 v. 1.7 Mb/si  In 1974, the use of DRAM was only 10% of the disk storage  It reached to the peak in 1986 when DRAM was 40% of the disk storage  This trend once again started reducing and was up to 15% in 1998 docsity.com Alternative Data Storage Technologies: Early 1990s Cap BPI TPI BPI*TPI Data Xfer Access Technology (MB) (Million) (KByte/s) Time Conventional Tape: Cartridge (.25") 150 12000 104 1.2 92 min. IBM 3490 (.5") 800 22860 38 0.9 3000 sec. Helical Scan Tape: Video (8mm) 4600 43200 1638 71 492 45 secs DAT (4mm) 1300 61000 1870 114 183 20 secs Magnetic & Optical Disk: Hard Disk (5.25") 1200 33528 1880 63 3000 18 ms IBM 3390 (10.5") 3800 27940 2235 62 4250 20 ms Sony MO (5.25") 640 24130 18796 454 88 100 ms docsity.com Devices: Magnetic Disks Purpose: – Long-term, nonvolatile storage – Large, inexpensive, slow level in the storage hierarchy Characteristics: – Seek Time (~8 ms avg) positional latency rotational latency docsity.com