EET 450 - Advanced Digital Chapter 8 Mass Storage.

EET 450 - 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

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 P1394 - 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 9.2Transfer Mode Cycle Time

nsSpeedMbps

Standard

PIO Mode 0 600 1.67 ATA

PIO Mode 1 383 2.61 ATA

PIO Mode 2 240 4.17 ATA

PIO Mode 3 180 11.1 ATA-2

PIO Mode 4 120 16.7 ATA-3

PIO Mode 5 90 22

DMA, sw, M 0 960 1.04 ATA

DMA, sw, M1 480 2.08 ATA

DMA, sw, M2 240 4.17 ATA

DMA, mw, M0 480 4.17 ATA

DMA, mw, M1 150 13.3 ATA-2

DMA, mw, M2 120 16.7 ATA-3

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 137.4 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 41-44 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 9.11 - transfer rate versus Cable length Addressing 15 devices

Table 9.11

SCSI

Termination – See figure 9.12 - 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