EEL 4709c- Computer Design
Chapter 6
External Memory
Team #6:
Adriana Andino
Janos Magasrevy
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Types of External Memory
• Magnetic Disk
– Magnetic Read and Write Mechanisms
– Data Organization and Formatting
• Optical Memory
– Compact Disk
– Digital Versatile Disk
• USB Memory Stick
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Magnetic Disk
• Disk substrate coated with magnetizable
material (iron oxide…rust)
• Substrate used to be aluminium
• Now glass
– Improved surface uniformity
• Increases reliability
– Reduction in surface defects
• Reduced read/write errors
– Lower flight heights (See later)
– Better stiffness
– Better shock/damage resistance
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Read and Write Mechanisms
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•
•
•
Recording & retrieval via conductive coil called a head
May be single read/write head or separate ones
During read/write, head is stationary, platter rotates
Write
– Current through coil produces magnetic field
– Pulses sent to head
– Magnetic pattern recorded on surface below
• Read (traditional)
– Magnetic field moving relative to coil produces current
– Coil is the same for read and write
• Read (contemporary)
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Separate read head, close to write head
Partially shielded magneto resistive (MR) sensor
Electrical resistance depends on direction of magnetic field
High frequency operation
• Higher storage density and speed
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Data Organization and Formatting
• Concentric rings or tracks
– Gaps between tracks
– Reduce gap to increase capacity
– Same number of bits per track (variable
packing density)
– Constant angular velocity
• Tracks divided into sectors
• Minimum block size is one sector
• May have more than one sector per block
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Disk Data Layout
• Messaging by audience
• Target consumer demographics
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Disk Velocity
• Bit near centre of rotating disk passes fixed
point slower than bit on outside of disk
• Increase spacing between bits in different
tracks
• Rotate disk at constant angular velocity (CAV)
– Gives pie shaped sectors and concentric tracks
– Individual tracks and sectors addressable
– Waste of space on outer tracks
• Lower data density
• Can use zones to increase capacity
– Each zone has fixed bits per track
– More complex circuitry
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Disk Layout Methods Diagram
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Finding Sectors
• Must be able to identify start of track and
sector
• Format disk
– Additional information not available to user
– Marks tracks and sectors
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Winchester Disk Format
Seagate ST506
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Optical Storage CD-ROM
• Originally for audio
• 650MB giving over 70 minutes audio
• Polycarbonate coated with highly reflective
coat, usually aluminium
• Data stored as pits
• Read by reflecting laser
• Constant packing density
• Constant linear velocity
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CD Operation: Material
44,100 samples/channel/second x 2 bytes/sample x 2 channels x
74 minutes x 60 seconds/minute = 783,216,000 bytes
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CD Operation: The Spiral
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CD Operation: Bumps
The incredibly small dimensions of the bumps make the spiral track
on a CD extremely long. If you could lift the data track off a CD
and stretch it out into a straight line, it would be 0.5 microns wide
and almost 3.5 miles (5 km) long!
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CD Operation: Reading the disk
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CD-ROM Drive Speeds
• Audio is single speed
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Constant linier velocity
1.2 ms-1
Track (spiral) is 5.27km long
Gives 4391 seconds = 73.2 minutes
• Other speeds are quoted as multiples (2X, 4X,
48X, etc.)
• Quoted figure is maximum drive can achieve
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CD-ROM Format
• Mode 0=blank data field
• Mode 1=2048 byte data+error correction
• Mode 2=2336 byte data
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Random Access on CD-ROM
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•
•
•
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Difficult
Move head to rough position
Set correct speed
Read address
Adjust to required location
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CD-ROM for & against
FOR:
• Large capacity (debatable)
• Easy to mass produce
• Removable
• Robust
AGAINST:
• Expensive for small runs
• Slow
• Read only
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Other Optical Storage
• CD-Recordable (CD-R)
– Now affordable
– Compatible with CD-ROM drives
• CD-RW
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Erasable
Getting cheaper
Mostly CD-ROM drive compatible
Phase change
• Material has two different reflectivities in
different phase states
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DVD what’s in a name?
• Digital Video Disk
– Used to indicate a player for movies
• Only plays video disks
• Digital Versatile Disk
– Used to indicate a computer drive
• Will read computer disks and play video disks
• Dogs Veritable Dinner
• Officially - nothing!!!
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DVD what’s in a name?
• DVD- Digital Versatile Disk. A technology for
producing digitized, compressed
representation of video information, as well as
large volumes of other digital data
• DVD-R – DVD Recordable
• DVD-RW – DVD Rewritable
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BD Blu-ray Disk
• Next Generation of Optical Disk
- HD- DVD
- 5 times storage capacity than traditional DVDs
• Blue-Violent Laser vs. Red Laser
- Shorter wavelength (405nm) than red laser (650nm)
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USB Memory
Stick
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Design and Implementation
One end of the device is fitted with a single male type-A USB connector. Inside the plastic casing is a
small printed circuit board. Mounted on this board is some simple power circuitry and a small number
of surface-mounted integrated circuits (ICs). Typically, one of these ICs provides an interface to the
USB port, another drives the onboard memory, and the other is the flash memory.
Drives typically use the USB mass storage device class to communicate with the host.
:: Essential components
• Male type-A USB connector. (1)
• USB mass storage controller. (2) (OTi-2168)
• NAND flash memory chip. (4)
• Crystal oscillator. (5)
:: Additional components
• Jumpers and test pins. (3)
• LEDs. (6)
• Write-protect switches. (7)
• Unpopulated space. (8)
• USB connector cover or cap.
• Transport aid.
• Expansion slot.
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OTi-2168 USB 2.0 Controller
It can control up to 8 pieces of flash memory. The controller has write-protected ability to prevent writing data to flash. Has one
LED control pin. Comprehensive application software for security function with Windows OS is also available.
This controller can operate in Win XP, Win2000, Windows Me, and Mac OS without any driver installation.
:: Features
● Mass storage class controller with Universal Serial Bus interface
● USB Specification Compliance
- Conforms to high-speed (480Mb/s) USB Specification, Version 2.0
- Meet bus power specification
● Integrated USB transceiver
- Dynamic feedback control
- Stable slew rate, independent of external loading
● Integrated USB Serial Interface Engine (SIE)
● Integrated RISC micro-controller
- High-performance RISC architecture
- Single cycle instruction execution
● 12 MHz external clock
● 3.3 V power operation
● Integrated PLL (Phase Lock Loop)
● Support up to 8 pieces of Flash memory with write-protected ability
● Support Infineon HYF33DS5128000ATC flash
● Support wear-leveling algorithm
● Higher reliability: ECC on the fly
● Automatic bad block management
● Supported OS:
Win XP, Win2K, Windows ME, Linux 2.4 above,
and MAC OS 9.0 & higher
Win 98/Win98SE driver available
Mac 8.6 mass storage driver available from Apple
● Support Auto-Run feature
● Configurable Vendor ID/Product ID (VID/PID)
● Small form factor - standard 48-pin TQFP and LQFP (7mmX7mm) package
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Uses
:: Personal data transport
:: Secure storage of data, application and software files
:: System administration
:: Computer repair
:: Application carriers
:: Computer forensics and law enforcement
:: Booting operating systems
:: Windows Vista ReadyBoost
:: Audio players
:: Music storage and marketing
:: Backup
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Advantages
:: Impervious to scratches and dust, and mechanically very robust.
:: Almost all personal computers support USB.
:: Store data relatively densely compared to many removable
media.
:: Power efficient, have no fragile moving parts, small and light.
:: Work without installing device drivers on the computer.
:: The operating system can use any file system or block
addressing scheme.
:: Extremely resistant to tough conditions.
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Advantages
YouTube video
Disadvantages
:: They can sustain only a limited number of write and erase
cycles before failure.
:: Most USB flash drives don’t include a write-protect
mechanism. Write-protection is suitable for repairing virusinfected host computers without the risk of infecting the USB
drive itself.
:: They are easily misplaced because of their small size. As a
consequence of this, some manufacturers have added
encryption hardware to their drives for data protection.
:: When they are compared to other portable storage device,
for example external hard drives, USB drives have a high
price per unit of storage and are only available in
comparatively small capacities.
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Comparison with other portable storage
:: Obsolete devices
:: Tape
:: Floppy disk
:: Optical media
:: External hard disk
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Review Questions
1. What are the advantages of using glass substrate for a magnetic disk?
Improvement in the uniformity of the magnetic film surface to increase disk reliability. A
significant reduction in overall surface defects to help reduce read/write errors. Ability to
support lower fly heights (described subsequently). Better stiffness to reduce disk dynamics.
Greater ability to withstand shock and damage.
2. How are data written onto a magnetic disk?
The write mechanism is based on the fact that electricity flowing through a coil produces a
magnetic field. Pulses are sent to the write head, and magnetic patterns are recorded on the
surface below, with different patterns for positive and negative currents.
3. How are data read from a magnetic disk?
In the traditional read mechanism, magnetic field moving relatively to the coil produces a
current. When the surface of the disk passes under the head it generates current of the same
polarity, as the one recorded on the disk.
.4. Explain the difference between a simple CAV system and a multiple
zoned recording system?
For the constant angular velocity (CAV) system, the number of bits per track is constant. An
increase in density is achieved with multiple zoned recording, in which the surface is divided
into a number of zones, with zones farther from the center containing more bits than zones
closer to the center..
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Review Questions
5. What is the typical sector size?
A) 256 bytes. B) 1024 bytes. C) 512 bytes. D) 128 bytes.
6. What’s the benefit of using Blue-Violet laser?
The benefit of using a blue-violet laser (405nm) is that it has a shorter wavelength than a red
laser (650nm), which makes it possible to focus the laser spot with even greater precision.
This allows data to be packed more tightly and stored in less space, so it's possible to fit more
data on the disc even though it's the same size as a CD/DVD. This together with the change of
numerical aperture to 0.85 is what enables Blu-ray Discs to hold 25GB/50GB
7. How long is the spiral track of a CD-ROM?
A) 5 miles. B) 5.27 km. C) 4270 meters. D) There’s no spiral track on a CD-ROM.
8. What are the essential components of a USB flash drive?
Male type-A USB connector, USB mass storage controller, NAND flash memory chip, and
crystal oscillator.
9. What is the data transfer speed specification for USB V2.0?
A) 600 Mb/s. B) 380 Mb/s. C) 480 Mb/s. D) 1 Gb/s.
10. What’s the layer composition of a CD-ROM?
Label, Acrylic, Aluminum, and Polycarbonate plastic.
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References: Book and Related Websites
 Book:
 Computer Organization and Architecture
By: William Stallings(Preferred)
 Websites:
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www.wikipedia.org
http://www.blu-ray.com/info/
http://electronics.howstuffworks.com/cd.htm
http://www.youtube.com/watch?v=NyOFIH-6WGs
http://www.bress.net/blog/archives/114-How-LongDoes-a-Flash-Drive-Last.html
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