Read And Write Amzb

Media And Storage ----------Write/Right mechanics Session 2 AM Zeus-Brown

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Your findings

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Quoting out of context and not looking at other papers Referencing (see dissc)

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◦ 

A lot of secondary reference's

Level of reading/research

Discussion from Self Study

Storage

examination

◦ You had been tasked to examine each of the device’s in turn make detailed notes and diagram ◦ Any problems Time management? Forensic awareness

LAB Session Discussion

Read/Write

mechanics for:

◦ Optical ◦ Solid state ◦ Magnetic

Topics For Today

A little bit of history

What’s

is inside

◦ The Platters ◦ The Spindle and Spindle Motor ◦ The Read/Write Heads ◦ The Head Actuator If you haven’t all ready make sure you watch the videos on black board as they will help you understand

Hard drive

Name the parts

Name the parts

Name the parts

Name the parts

Name the parts

Name the parts

Data is stored on the surface of a platter in sectors and tracks.  Tracks are concentric circles, and sectors are pie-shaped 

wedges on a track, like this: Yellow = Track Blue = Sector Sectors contain a fixed number of bytes Sectors are grouped at either drive or OS level Low level format writes tracks and sectors, start & end point High level Format write the file storage structures (file allocation table)

Tracks and sectors

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The drive channel electronics receive data in binary form from the computer and converts them into a current in the head coil. The current in the coil reverses at each 1 and remains the same at each 0.

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This current interaction with the media results in magnetization of the media, which direction depends on the current direction in the coil.

Magnetic Read/Write

MR Reading Head Shields

Inductive Writing head poles Coils

MR Sensor

Hard Disk Mechanics



The big differences 1. .

2. .

3. .

4. .

Tape has a thin strip of plastic on to which the recording coating is applied HDD is layered on high-precision aluminium or glass disc Tape has a slow seek speed Fast forward etc. This can take 5 minutes plus with a large tape HDD can move to any part of the surface almost instantly Tape drive read/write heads touch the tape (can cause damage over time) HDD read/write head flies across surface never touching it Tape head moves at about 2” (5.08cm) per second HDD can spin the platter under the head at 3,000” per second (about 170mph or 272khp) these speed are increasing

Cassette Tape vs. Hard Disk

Optical CD/DVD/ HD Disc/Blueray Disc

Spot

(Beam) diameter

◦ wavelength of light / Numerical Aperture

Depth

of focus

◦ wavelength of light / (Numerical Aperture)2 For the current optical storage systems, the depth of focus is about 1 mm.

Optical Read/Write

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44,100 samples/channel/second x 2 bytes/sample x 2 channels x 74 minutes x 60 seconds/minute = 783,216,000 bytes

CD Cross Section

CD

 Spiral

from centre out towards the edge  Tracks are very small approximately .5 microns wide

CD

0.5 microns 1.6 microns

Reading the bumps

0.5 microns

Optical drive

Spinning CD

Digital Signal

LASER

Optical Pickup

Laser Focus

500 rpm

450 rpm Tracking Motor 74 min 350 rpm

Disc Motor Laser Date____________ Label___________

0 rpm The CD player spins the disc while moving the laser assembly outward from the middle. To keep the laser scanning the data track at a constant speed, the player must slow the disc as the assembly moves outward.

STAMPED CD

Stamped/pre-pressed CD

Label Aluminium Dye Darken = 0 Leave translucent =1

Polycarbonate Plastic

Write Writing CD

CD-R

A

CD-R doesn't have the same bumps and lands as a conventional CD. Instead, the disc has a dye layer underneath a smooth, reflective surface. On a blank CD-R disc, the dye layer is completely translucent, so all light reflects. The write laser darkens the spots where the bumps would be in a conventional CD, forming nonreflecting areas.

What's it doing

CD drive

CD drive

Label Aluminium Phase change compound

Darken = 0 Leave translucent =1

Polycarbonate Plastic

CD-RW Write Erasing Writing Erase data CD data

Dielectric layers

Heat

then rapid cool = write Heat and controlled cool = erase

Phase-change Compounds

Solid State/flash Memory MOSFET (Meta-Oxide-Semiconductor FieldEffect Transistor)

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few examples of Flash memory: ◦ ◦ ◦ ◦ ◦

Your computer's BIOS chip CompactFlash (most often found in digital cameras) SmartMedia (most often found in digital cameras) Memory Stick (most often found in digital cameras) PCMCIA Type I and Type II memory cards (used as solid-state disks in laptops) ◦ Memory cards for video game consoles 

Use’s an electric field to switch Between 1 and 0

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When erasing I erases blocks Or the entire chip rather than one byte like EEPROM does.

Flash memory

1. 2. 3. 4. 5. 6. 7. 8.

USB connector USB mass storage controller device Test points Flash memory chip Crystal oscillator LED Write-protect switch Space for second flash memory chip

Inside a USB

Internals of a typical flash drive (Saitek brand USB1.1 pictured)

System administration Computer repair Application carriers To boot OS Windows vista ReadyBoost Personal data transport Audio players Music storage In arcades

Common uses

Strengths

◦ Flash drives are nearly impervious to the scratches and dust ◦ USB drives will work in most places ◦ Don’t need additional device drivers ◦ Can be used as a boot device

Strengths and weaknesses

Flash

drives can only sustain a limited number of write and erase cycles ◦ Mid range drives support several thousand cycles ◦ This should be considered when using flash drives to run applications

Weaknesses

NOR

memories (DDR, the memory inside your pc) NAND memories (USB memory stick) ◦ NOR and NAND flash differ in two important ways: the connections of the individual memory cells are different the interface provided for reading and writing the memory is different ◦ (NOR allows random-access for reading, NAND allows only block access)

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floating-gate transistor to act like an electron gun. Word line

Control Gate

Bit line

Thin Oxide layer -> (-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)

Drain

Floating Gate

Source Current Flow

(-)(-)(-)(-)(-)

Negatively charged electrons

Fowler-Nordheim tunneling

1 0

Some

drives feature Encryption

◦ Generally using full disk encryption below the file system Flash

drives can be extremely small proving a problem for companies and data leaks Its also possible to run malicious software such as rootkits or packet sniffers

Security

Interfaces Self Study ACW1



IDE



EIDE



UDMA



ATA

   

  

◦ Integrated Drive Electronics ◦ Enhanced Integrated Drive Electronics ◦ Ultra Direct Memory Access ◦ Advanced Technology Attachment

ATAPI

◦ ATA Packet Interface

SCSI

◦ Small Computer Systems Interface

Firewire

◦ IEEE1394

USB

◦ Universal Serial Bus

Parallel Serial FC-AL

◦ Fibre Channel-Arbitrated Loop

Interface’s

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Report on one of the interfaces Presenting your findings next week in this session

Decide which interface would be best for the following and why 1. Portable storage device. 2. Large (800gig+)Hard disk drive 3. External hard disk drive

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Presenting your findings next week in this session

Discussion from Self Study