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Lecture #39: Magnetic memory storage

Lecture #39: Magnetic memory storage. Last lecture: Dynamic Ram E 2 memory This lecture: Future memory technologies Magnetic memory devices Hard drives, tape drives, Optical disks. Future memory technologies.

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Lecture #39: Magnetic memory storage

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  1. Lecture #39: Magnetic memory storage • Last lecture: • Dynamic Ram • E2 memory • This lecture: • Future memory technologies • Magnetic memory devices • Hard drives, tape drives, Optical disks EE 42 fall 2004 lecture 39

  2. Future memory technologies • Memory speed, cost and density are among the chief bottlenecks on compute power. • Increasing CPU clock rates have only resulted in small increases in speed of operation due to the memory system and mass storage (disk) I/O bottleneck. • A significant amount of research effort is directed to improving memory technology EE 42 fall 2004 lecture 39

  3. Advanced memory technologies • Ferroelectric Random Access Memory (FRAMs) • Magnetoresistive Random Access Memories (MRAMs) • Tunneling Magnetic Junction RAM (TMJ-RAM): • Experimental Memories • Quantum-Mechanical Switch Memories • Single Electron Memory EE 42 fall 2004 lecture 39

  4. FRAM EE 42 fall 2004 lecture 39

  5. Ferroelectric material EE 42 fall 2004 lecture 39

  6. TMJ-Ram • Tunneling Magnetic Junction RAM (TMJ-RAM): • Speed of SRAM, density of DRAM, non-volatile (no refresh) • “Spintronics” (electron spin affects transport) • Same technology used in the read heads of high-density disk-drives: Giant magneto-resistive effect EE 42 fall 2004 lecture 39

  7. Tunneling Magnetic Junction EE 42 fall 2004 lecture 39

  8. Mass Storage • For storage of larger amounts of information, magnetic film storage dominates • Information is stored in the form of magnetic domains in a Ferromagnetic film, written or read by a moving head EE 42 fall 2004 lecture 39

  9. Magnetic domains • Ferromagnetic materials have a quantum interaction which makes adjacent atoms line up their magnetic field in the same direction N N N N N N N N N N N N N S S S S S S S S S S S S S EE 42 fall 2004 lecture 39

  10. Magnetic interactions • On a larger scale, magnets feel a force to line up in opposing directions, reducing the total magnetic field. • For example, if you try to hold two magnets next to each other, there will be a strong force which will rotate them to the configuration: N S S N EE 42 fall 2004 lecture 39

  11. Magnetic domains • If you look microscopically at a magnetic material, it forms domains, or areas where the magnetic poles are aligned, adjacent to regions where the magnetization is in the opposite direction. • In a thin film, the domains look like this: EE 42 fall 2004 lecture 39

  12. Moving magnetic domains • Magnetic domains don’t move easily at room temperature, but they can be changed by applying magnetic fields. • If most of the domains in a material are aligned in one direction, we call it a permanent magnet. • The core of an inductor or a transformer is made of a ferromagnetic material where the domains line up easily, and then randomize again when the external field is turned off EE 42 fall 2004 lecture 39

  13. Writing to magnetic media • Magnetic storage material is comprised of a thin film of ferromagnetic material which is relatively magnetically hard. • A small electromagnet is used to create domains oriented in a particular direction EE 42 fall 2004 lecture 39

  14. Reading magnetic material • Conventional read heads for magnetic media work just like the secondary winding of a transformer. • Instead of a primary winding changing the magnetic field through a coil, and thus changing the voltage, the magnetic media is moved next to the read coil. • This produces a voltage across the read coil which can be amplified and translated as data EE 42 fall 2004 lecture 39

  15. Transformer + V1 - + V2 - Transformer EE 42 fall 2004 lecture 39

  16. 9 v. 22 Mb/si 470 v. 3000 Mb/si 0.2 v. 1.7 Mb/si source: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even more data into even smaller spaces” Storage density for DRAM vs DISK EE 42 fall 2004 lecture 39

  17. SRAM vs. DRAM vs. Disk • Access latencies: • DRAM ~10X slower than SRAM • Successive bytes 4x faster than first byte for DRAM • Disk ~100,000X slower than DRAM • First byte is ~100,000X slower than successive bytes on disk EE 42 fall 2004 lecture 39

  18. Nano-layered Disk Heads • Recent large improvement in Disk capacity comes from “Giant Magneto-Resistive effect” (GMR) read heads Coil for writing EE 42 fall 2004 lecture 39

  19. Typical Numbers of a Magnetic Disk Track Sector • Rotational Latency: • Most disks rotate at 3,600 to 15,000 RPM • Approximately 16 ms to 4 ms per revolution, respectively • An average latency to the desiredinformation is halfway around the disk: 8 ms at 3600 RPM, 2 ms at 15,000 RPM • Transfer Time is a function of : • Transfer size (usually a sector): 1 KB / sector • Rotation speed: 3600 RPM to 10000 RPM • Recording density: bits per inch on a track • Diameter typical diameter ranges from 2.5 to 5.25 in • Typical values: 2 to 80 MB per second Cylinder Platter Head EE 42 fall 2004 lecture 39

  20. Inner Track Outer Track Sector Head Arm Platter Actuator Disk Device Terminology • Several platters, with information recorded magnetically on both surfaces (usually) • Bits recorded in tracks, which in turn divided into sectors (e.g., 512 Bytes) • Actuator moves head (end of arm,1/surface) over track (“seek”), select surface, wait for sector rotate under head, then read or write • “Cylinder”: all tracks under heads EE 42 fall 2004 lecture 39

  21. { Platters (12) Photo of Disk Head, Arm, Actuator Spindle Arm Head Actuator EE 42 fall 2004 lecture 39

  22. Disk Device Performance Inner Track Outer Track Sector Head Controller Arm Spindle • Disk Latency = Seek Time + Rotation Time + Transfer Time + Controller Overhead • Seek Time? depends no. tracks move arm, seek speed of disk • Rotation Time? depends on speed disk rotates, how far sector is from head • Transfer Time? depends on data rate (bandwidth) of disk (bit density), size of request Platter Actuator EE 42 fall 2004 lecture 39

  23. Disk Device Performance • Average distance sector from head? • 1/2 time of a rotation • 7200 Revolutions Per Minute  120 Rev/sec • 1 revolution = 1/120 sec  8.33 milliseconds • 1/2 rotation (revolution)  4.16 ms • Average no. tracks move arm? • Sum all possible seek distances from all possible tracks / # possible • Assumes average seek distance is random • Disk industry standard benchmark EE 42 fall 2004 lecture 39

  24. Response time = Queue + Controller + Seek + Rot + Xfer Service time Devices: Magnetic Disks Track Sector • Purpose: • Long-term, nonvolatile storage • Large, inexpensive, slow level in the storage hierarchy • Characteristics: • Seek Time (~8 ms avg) • positional latency • rotational latency • Transfer rate • 10-30 MByte/sec • Blocks • Capacity • Gigabytes • Quadruples every 3 years (aerodynamics) Cylinder Platter Head 7200 RPM = 120 RPS => 8 ms per rev ave rot. latency = 4 ms 128 sectors per track => 0.25 ms per sector 1 KB per sector => 16 MB / s EE 42 fall 2004 lecture 39

  25. Areal Density • Bits per unit area changed slope from 30%/yr to 60%/yr about 1991 EE 42 fall 2004 lecture 39

  26. Technology Trends Disk Capacity now doubles every 12 months; before 1990 every 36 motnhs • Today: Processing Power Doubles Every 18 months • Today: Memory Size Doubles Every 18-24 months(4X/3yr) • Today: Disk Capacity Doubles Every 12-18 months • Disk Positioning Rate (Seek + Rotate) Doubles Every Ten Years! The I/O GAP EE 42 fall 2004 lecture 39

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