Chapter 6 – External Memory
Magnetic
Disk
Group # 6
•Ramon Canseco
•Jorge Mora
•Ibrahim Babun
•Dominic Tang How
•Bao Kun
•Ricardo Gonzalez
What is a Magnetic disk?
Circular platter constructed of non-magnetic
material, the material is called substrate,
coated with a magnetizable material.
 Recently the use of glass substrate have
introduce the following benefits:

◦ Improve uniformity of the magnetic film, to
increase reliability.
◦ Reduces read-write errors
◦ Better stiffness to reduce disk Dynamics
◦ Greater ability to withstand shock and damge.
Key points of magnetic disk
Remain the most
important
component of
external memory.
 Used in system
raging from personal
computer to super
computer.

Both removable and
fixed, or hard disk.
 For greater
performance and
larger server system
a RAID disk is used.
Also later on, you
will learn about
optical storage.

Magnetic disk write mechanism

Data are recorded on and later retrieved
from the disk via a conducting coil named
the head.
◦ In many system there are two heads:
 A read head and a write head.

During the write mechanism the head is
stationary while the patter rotates
beneath it.
Write mechanism
Electricity flows through a coil that
produces a magnetic filed.
 Electric pulses are sent to the write head:

◦ Resulting in the magnetic patterns recorded.
Data Organization and Formatting


Tracks are a concentric set of
rings on the platter.
Tracks are separated by Gaps.
Gaps prevent errors due to
misaligned heads.


Sectors is how data is transferred
to and from disk.
Constant Angular velocity is the
disk at a fixed speed.
Advantage:

The advantage of using
CAV is that individual
blocks of data can be
directly addressed by track
and sector.
Disadvantage:

The disadvantage of CAV is
that the amount of data
that can be stored on the
long outer tracks is the
only same as what can be
stored on theshort inner
tracks.
Constant Angular Velocity

A removable disk can be
removed and replaced with
another disk.

A non-removable disk is
permanently mounted in the
disk drive; the hard disk in a
personal computer is a nonremovable disk.

Movable-head disk, there is
only one read-write head.
Physical Characteristics
Winchester Disk Format
(Seagate ST506)
•The ST-506 was the first 5.25 inch hard
disk drive.
•Introduced in 1980 by Seagate Technology
•It stores up to 5 megabytes after
formatting and cost $1500
•The term Winchester was originally used by IBM as a code name for the 3340 disk model prior to
its announcement.
•The 3340 was a removable disk pack with the heads sealed within the pack. The term is now
applied to any sealed-unit disk drive with aerodynamic head design. The Winchester disk is
commonly found and built into personal computers and workstations, where it is referred to as
a hard disk.
Disk Performance Parameters
T = b/rN
 Where :

◦
◦
◦
◦


T transfer time
b number of bytes to be transferred
N number of bytes on a track
r rotation speed, in revolutions per second
Thus the total average access time can be expressed as
Ta = Ts + 1 /(2r) + b/rN
Where Ts is the average seek time.
Size/Performance/Uses differs
What is Raid???
RAID
(Redundant Array of Independent Disks )
-RAID
is a technology that provides increased storage
functions and reliability through redundancy.
- The RAID scheme consists of seven levels,
zero through six.
- The RAID strategy employs multiple disk drives
RAID 0
(also known as a stripe set or striped volume)

Following are the key points to remember for RAID level 0.
- Minimum 2 disks.
- Excellent performance ( as blocks are striped ).
- No redundancy ( no mirror, no parity ).
- Don’t use this for any critical system.
RAID 1

Following are the key points to remember for RAID level 1.
- Minimum 2 disks.
- Good performance ( no striping. no parity ).
- Excellent redundancy ( as blocks are mirrored ).
the important aspect of this RAID is that information on one disk or
partition is being replicated.
RAID 2
(bit-level striping with dedicated Hamming-code parity)

RAID 2 requires fewer disks than RAID 1

A RAID 2 stripes data at the bit (rather than block)

uses Hamming code for error correction

The use of Hamming code permits using 7 disks in RAID 2

Because of its high cost and complexity, RAID 2 never really caught on
RAID 3
byte-level striping with dedicated parity
 only a single redundant disk
 parallel access with small strips of data
 Reconstruction of parity disks

Advantages
Disadvantages
Very high read and write
data transfer rate
 Insignificance impact from
disk failure
 Efficient low ratio of parity
disks to data



Transaction rate equals to
single disk drive
Complex controller design
RAID 3
RAID 4
block-level striping with dedicated parity
 independent access array
 allows I/O requests to be performed
 strips are relatively large
 bit-by-bit parity strip is calculated

Advantages


Disadvantages
Very high read data
transaction rate
Efficient low ratio of parity
disks to data



Quite complex controller
design
Worst write transaction
and write aggregate
transfer rates
Difficult and inefficient data
rebuild
RAID 4
RAID 5
block-level striping with distributed parity
 distributes the parity strips across all
disks
 round-robin scheme
 avoids the bottleneck found in RAID 4.

Advantages
Disadvantages
Highest read data
transaction rate
 Good aggregate
transfer rate
 Efficient low ratio of
parity disks to data



The most complex
controller design
Difficult to rebuild during
disk failure
RAID 5
RAID 6
block-level striping with double distributed
parity
 two different parity calculations
 stored in separate blocks on different disks
 extremely high data availability

Advantages


Disadvantages
Extremely high data fault
tolerance
Sustain multiple
simultaneous drive failures


More complex controller
design
Controller overhead is
extremely high
RAID 5
Optical Memory
Optical Disk Products

CD
◦ CD-ROM; CD-R; CD-RW;

DVD
◦ DVD-R; DVD-RW

Blu-Ray
CD Operation
Basic One-Side Disc Operation
Double-Sided Disc Operation
CD-ROM Block Format
SYNC: Identifies the beginning of a block.
Header: Contains the block address and the mode byte.
Mode 0: Specifies a blank data field
Mode 1: Specifies the use of error-correction= 2048 bytes
Mode 2: Specifies 2336 bytes of user data with no error correcting code.
Auxiliary: Additional user data in mode 2. 288 bytes used as error-correcting code in Mode 1
High Definition Optical Disks
-Blu Ray:
-Same size as CDs and DVD (1.2mm)
- Contains 25GB of data per layer
-Available with Triple (100GB) and Quadruple
(128GB) Layers
-The name Blu-ray refer to blue laser used to
-read disc
HD DVD
-No longer in production
-Lost optical disc war to Blu Ray
Example of
High -Definition
Questions

For CDs and DVDs, what does, pits and
lands ( no change in elevation) converts
to in digital signals?

What was a major factor in the Blu Ray,
HD DVD optical disk war?
6.4 MAGNETIC TAPE
Magnetic Tape
Sequential access
 Serpentine recording
 Very cheap
 Backup and archive
 Linear Tape-Open (LTO) Tape Drives

◦ Developed late 1990s
◦ Open source alternative to proprietary tape
systems
Linear Serpentine Recording
Access to data

Move from record 1 to
N.
◦ Read records 1 through
N-1 one at a time

If beyond N
◦ Rewind tape x distance
and begin reading

Tape Directory
◦ Physical tape location for
a given data block
◦ Detected while winding
tape
Linear Tape-Open (LTO) Tape Drives
LTO-1
LTO-2
LTO-3
LTO-4
LTO-5
LTO-6
Release date
2000
2003
2005
2007
2010
TBA
Compressed
capacity
200 GB
400 GB
800 GB
1600 GB
3 TB
8 TB
Compresses
transfer rate
(MB/s)
40
80
160
240
280
525
Linear Density
(bits.mm)
4880
7198
9638
13300
15142
Tape tracks
384
512
704
896
1280
Tape length
609 m
609 m
680 m
820 m
846 m
Tape width (cm)
1.27
1.27
1.27
1.27
1.27
Write elements
8
8
16
16
16
USB flash driver
Universal Serial Bus—Flash—Driver
Name and Definition

As the name of this device, What USB
flash driver is a driver which using flash
memory chip as its storage media and
communicating with computer or other
device via Universal Serial Bus.
Universal Serial Bus

it is an industry standard developed in the
mid-1990s that defines the cables,
connectors and protocols used for
connection, communication and power
supply between computers and electronic
devices.
Device classes

USB defines class codes used to identify a
device’s functionality and to load a device
driver based on that functionality. This
enables every device driver writer to
support devices from different
manufacturers that comply with a given
class code.Device classes include:
Class
Usage
Description
Examples, or exception
Device class is unspecified, interface descriptors are used
to determine needed drivers
00h
Device
Unspecified[12]
01h
Interface
Speaker, microphone, sound card, MIDI
02h
Both
03h
Interface
Audio
Communications and CDC
Control
Human interface device (HID)
05h
06h
Interface
Interface
Physical Interface Device (PID)
Image
Force feedback joystick
Webcam, scanner
07h
Interface
Printer
Laser printer, inkjet printer, CNC machine
08h
Interface Mass storage
09h
Device
USB hub
0Ah
Interface
CDC-Data
0Bh
0Dh
0Eh
0Fh
Interface
Interface
Interface
Interface
Smart Card
Content security
Video
Personal Healthcare
USB smart card reader
Fingerprint reader
Webcam
Pulse monitor (watch)
DCh
Both
Diagnostic Device
USB compliance testing device
E0h
EFh
Interface
Both
Wireless Controller
Miscellaneous
Bluetooth adapter, Microsoft RNDIS
ActiveSync device
Application-specific
IrDA Bridge, Test & Measurement Class (USBTMC),[13] USB
DFU (Direct Firmware update)[14]
FEh
Interface
Modem, Ethernet adapter,Wi-Fi adapter
Keyboard, mouse, joystick
USB flash drive, memory card reader, digital audio
player, digital camera, external drive
Full bandwidth hub
Used together with class 02h: communications and CDC
control
USB 1.1 and before；USB 2.0
•
•
USB 1.0: Released in January
1996.
Specified data rates
of 1.5 Mbit/s (Low-Bandwidth)
and 12 Mbit/s (Full-Bandwidth).
Does not allow for extension
cables or pass-through
monitors (due to timing and
power limitations). Few such
devices actually made it to
market.
USB 1.1: Released in
September 1998.
Fixed problems identified in
1.0, mostly relating to hubs.
Earliest revision to be widely
adopted.


USB 2.0: Released in April 2000.
Added higher maximum
bandwidth
of 480 Mbit/s (60 MB/s) (now
called "Hi-Speed"). Further
modifications to the USB
specification have been done via
Engineering Change Notices
(ECN). The most important of
these ECNs are included into
the USB 2.0 specification
package available from USB.org
On-The-Go Supplement 1.3:
Released in December 2006.
USB On-The-Go makes it
possible for two USB devices to
communicate with each other
without requiring a separate
USB host. In practice, one of
the USB devices acts as a host
for the other device.
USB 3.0 and future

There have been many reports of USB 3.0
equipment only transferring data at USB 2.0
speed, usually with a message "This USB
Mass Storage Device can transfer
information faster if you connect it to a
Super-Speed USB 3.0 port". This has been
due to several causes, including drivers,
certain cables specified as USB 3.0
(problems disappeared when a different
cable was used), order of starting equipment,
equipment needing to be disconnected and
reconnected, and overclocked computers
Flash


Flash memory (either NOR or NAND-type type) is
invented by Dr. Gang Fujio from Toshiba
Corporation in 1984.According to Toshiba Flash the
name "Flash" is following colleagues suggested.
Because the memory erase process reminded him
of the camera's flash. Dr. Gang Fujio San Francisco,
California in 1984 IEEE
International Conference electronic
components(International Electron Devices Meeting,
IEDM)published the invention. Intel saw the great
potential of this invention, and in 1988 launched the
first commercial NOR Flash chips
SLC


Traditionally, each memory cell stores one bit of
information, called single-stage storage unit(singlelevel cell, SLC), the use of this storageunit, also known
as single-stage flash flashmemory cell (SLC flash
memory), or simply SLC flash memory. SLC flash
memory has the advantage of faster transmission
speed, lower power consumption and memory
cells live longer.However, because each memory
cell containsless information, it takes a
higher per megabytecost to
produce.As fast transmission speed, SLC flash
technology will be used in high-performance memory
card.
MLC


Multi-stage flash memory storage unit (Multi-level cell flash
memory, MLC flash memory) can be stored in each memory
cell within the two or more bits of information, its "multistage" refers to the charge can charge more than
one order (ie, more a voltage value), so the value can store
multiple bits in each storage unit. Borrow from each memory
cell can store more bits, MLC flash memory can reduce
production costs, compared with SLC
flash, its slow transmission speed,
power consumption and high life of the lower storage unit,
so the MLC flash memory technology will be used in
the standard type of memory card. In addition,
the flying cable semiconductor Mirror Bit ® technology, also
belong to this type of technology.
References:
http://www.computerrepairinvictoria.com/
images/raidarticle_whatis.gif
 http://www.google.com/search?um=1&hl=
en&biw=824&bih=830&tbm=isch&sa=1&q
=Hard+drive&oq=Hard+drive&aq=f&aqi=
g10&aql=&gs_sm=e&gs_upl=6292l8120l0l
8580l10l7l0l0l0l0l214l11
 http://en.wikipedia.org/wiki/External_Me
mory_Interface

Hope you enjoyed our
presentation!!