EET Advanced Digital Chapter 8 Mass Storage

Technologies One of the primary ‘blocks’ of the computer system is Mass Storage. Store large amounts of Data and Program information, available quickly –Not as fast as Main Memory –Speeds can be improved with Cache

Technologies Magnetic –can detect the change of a magnetic field motion varying field –A wire must break the lines of magnetic flux Materials –iron, nickel, cobalt

Technologies –materials dictate issues of speed (coercivity), life of stored information (retentivity) Magneto-Optical –use laser to direct magnetic field in recording data image –laser alone is used to read –Very high storage density

Technologies Optical –CD technology used to optically record and read digital information. CD DVD CDR CDRW

Types of Mass Storage Hard Disks Floppy Disks PC Cards Magneto-optical Drives CD-Rom/CDR/CDRW –DVD ROM / DVD Ram Tape Drives

Magnetic Optical Solid State

Access Random Access –Any bit w/in access time for device Sequential –Tape drive New Technologies –DVD - optimized for sequential access, but does random

Magnetic Media Based on some form of magnetic compound –Wire –Tape - mylar with magnetic compound adhered to it. –Disks/Drums/Platters

Magnetic Media magnetism and electricity are related –moving a wire in a magnetic field generates electrical current –running a current through an electrical wire produces a magnetic field The magnetic materials - iron, nickel, cobalt are the common ones - consist of small particles with magnetic properties

Magnetic Media At the small level, these particles can be viewed as a group of little magnets. These little magnets are originally in Random order. By imposing a magnetic field, the little magnets line up. When these lined up magnets are MOVED near a wire – electricity.

Magnetic Media

The affect of magnetic field or induced current is magnified at a gap Only a change in magnetic field can be detected These CHANGES are used to encode digital information

Recording Methods to record magnetic information, a timed sequence of flux transitions occurs. Recording –Frequency Modulation - FM –Modified Frequency Modulation - MFM Saves space by eliminating clock pulses –Run Length Limited - RLL

Drives Older technology drives were delivered unformatted –Using a low level program, the drive was formatted - writing sector information and tracks –The disk would then be partitioned –The OS must then format the partition Current versions - IDE, Ultra, SCSI, etc. do not require low level formatting.

Drives Various methods of data compression have been used to increase storage space compression, typically software based, took up speed by loading the main processor with compression/decompression responsibilities.

Hard Drives Increased storage has been gained, by advanced formulations of magnetic compounds. more precise movement in mechanisms more precise manufacturing - leading to smoother, more even emulsion layers. Fast rotation speeds and powerful head movement mechanisms

Advanced Storage Systems Drive Arrays –RAID Parallel Access Arrays Magneto-Optical systems –Optically assisted magnetic write with, optical read –magnetically erased –SLOW

Drive Interfaces The physical drive has limitations for size and speed. The electronic connection to the ‘system’ imposes it’s own limitations. See Table 9.1 –note that transfer rate is the only figure of merit in this table (besides # of devices)

Table 9.1

Drive interfaces Note P fire wire FC-AL: Fiber Channel-Arbitrated Loop –SSA System Storage Arch. Aaron -a blend of fiber connections Current USB is being used –see Apple G3

Performance of AT drives see Table 9.2 –speeds to 16 Mbps

Table 9.2

Addressing Limit Legacy limit of drive size - –DOS imposed 504Mb limit Solution - bypass INT13h access of drives

ATAPI AT Attachment interface with Packet control commands for CDRom and Tape drives

Implementations ATA EIDE ATA-2 (Fast-ATA) –Up to GB ATA-3 –Added S.M.A.R.T. (Self-Monitoring, Analysis and Reporting Technology)

ATA/ATAPI ATA/ATAPI-4 – Packet Int. Ext –Defined 80 cond. 40 pin cable –UDMA/33 –Enhanced BIOS for over 9.4 trillion gigabytes (ATA is still <= 137.4GB) ATA/ATAPI-5 – w/ Packet Int. –Requires 80 conductor cable for UDMA/66

Physical Wiring Drive Cables –Terminated cable end –40 pin cable - ribbon –44 pin connector - pins provide power 50 pin variant - provides drive selection –68 pin connector - PC Card Pin assignments - see table 9.7 Power

Master/Slave selection ATA - supports two drives per channel Choices –Master –Slave –Only Drive

SCSI Small Computer System Interface SCSI-1,2,3 Advanced SCSI –Wide SCSI - 32 bit wide –Ultra SCSI 10 MHz timing - 40 Mb/sec transfer Table transfer rate versus Cable length Addressing 15 devices

Table 9.11

SCSI Termination –See figure page 459 Connectors –25 pin D type connectors –50 pin amphenol –68 pin - Wide SCSI-2/3 devices

Floppy Drive connections 34 pin ribbon termination twist

Power Connections + 12 V for motor controls on some drives + 5 V for logic Some older drives with ROM on board may require -12v, etc. but this is not typical in today’s systems. Two connector types - D shaped, ‘3.5 inch drive’ type

Other connections legacy connections - MFM/RLL type –separate data cables