CIS 141 LectureStorage Hardware (saving data/information)

Thad Crews

Western Kentucky University

SAVING INFORMATIONSTORAGE HARDWARE

(Remember: Digital vs. Analog)

•Digital systems have discrete values 1 / 2 / 3 / 4 / 5On / Off

• Digital with two states is called Binary

•Analog systems have continuous data values

(Remember: Bits and Bytes)

•A bit (e.g., “binary digit”) is a single one (1) or zero (0).

•Eight bits is a byte – the standard grouping in digital electronics

•1’s and 0’s can be used to represent:• Numbers• Letters• Sounds• Images• Videos

INPUT PROCESS

• CPU• Memory

OUTPUT

Input – Process – Output

INPUT PROCESS

• CPU• Memory

OUTPUT

Storage

This memory is volatile which means it requires electrical power to hold its value.

STORAGE

INPUT PROCESS

• CPU• Memory

OUTPUT

Storage

• Hard Disk (magnetic)• CD/DVD/BD (optical)• USB Flash (solid

state)

“RAM”“Memory”“Main Memory”

“Secondary Memory”“Storage”

Main Memory vs. Storage Memory is volatile — holds data and instructions temporarily

Storage is nonvolatile — contents retained when power is off

So why not use “Storage” hardware for “Main Memory”?

Memory/Storage Hierarchy

CPU

Cache (L1, L2)

RAM (main memory)

Solid State (Flash) Storage

Magnetic Storage

Optical Storage

Faster Data Transfer & More Expensive

Slower DataTransfer &Less Expensive

Solid State Storage (Storage 1 of 3)

•Flash memory resides on a chip (e.g., solid state; no moving parts; like RAM.) However, flash memory is nonvolatile so it retains its information when it is “unplugged.”

A single 8GB USB/thumb/flash drive stores as much data as 1,000+ CDs

A single 8GB USB/thumb/flash drive stores as much data as 1,000+ CDs

Mini Memory Card

Magnetic Storage (Storage 2 of 3)

•A hard disk is the most common magnetic storage media, consisting of several inflexible platters covered with magnetic material enclosed in an airtight, sealed case.

•Hard drive platters spin at a rate of ~8000 RPM.

The read/write head

Hard Disk

•A head crash occurs when the read/write head touches the platter surface.

Do NOT shake your machine while your hard drive is spinning.

Do NOT shake your machine while your hard drive is spinning.

Clearance between head and platter is approximately two-millionths of an inch

Hard Disks

•A Redundant Array of Independent Disks (RAID) connects multiple disks into a single unit to achieve high levels of storage reliability.

Older magnetic storage media

•Floppy disks•Tape drives

Solid State Drive vs. Hard Disk Drive

Your next computer may have a solid state drive (SSD) instead of a hard drive.• SSD Advantages:

• Faster (no spin start up, no moving head seek)

• Silent operation due to lack of moving parts

• Low power consumption• Generate little heat• Low failure rate

• SSD Disadvantages• More expensive per gigabyte• Great difference between write

speed and read speed (may cause problems)

SSD (Solid State Disks) Many competing standards

Optical Media Storage (Storage 3 of 3)

•CD, DVD, Blu-laser Disc (BD) are all optical media that use a laser to read and write the data on the disc.

Note: Magnetic disks are spelled with a “K”, and optical discs are spelled with a “C”.

Note: Magnetic disks are spelled with a “K”, and optical discs are spelled with a “C”.

Optical Discs

How does a laser read data on an optical disc?

laserdiode

laserdiode

prism prism

light-sensing

diode

light-sensing

diode

0 1

lens lenspit land

disc label

Step 1.Laser diode shines a light beam towarddisc.

Step 2.If light strikesa pit, it scatters. If light strikes a land, it is reflected back toward diode.

Step 3.Reflected light is deflected to alight-sensing diode, which sends digital signals of 1 to computer. Absence of reflected light is read as digital signal of 0.

Optical Discs

•CD, DVD, Blu-laser Disc (BD)

1 CD = 486 Floppy Disks1 DVD = 3,263 Floppy Disks

1 BD = 17,361 Floppy Disks

1 CD = 486 Floppy Disks1 DVD = 3,263 Floppy Disks

1 BD = 17,361 Floppy Disks

Recent News Stories about Storage

•NSA Spy Center: • Read more here

•White House Shares $200 Million Big Data Plan: • Read more here

•60th Anniversary of Tape Storage:• Read more here

SUMMARY (Computer Hardware)

Ch7

Ch6 Ch

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Ch8

Quiz1

(Remember: Prefixes)• A byte is about the size it takes to store a letter of the alphabet.

• A kilobyte is about the storage you would need for a six-page paper.

• 1.44 megabytes: A floppy disk.

• 500 megabytes: CD-ROM

• 4.7 gigabytes: DVD Disc

• 25 gigabytes: Blu-Ray Disc

• 1 terabyte: All the X-ray films in a large technological hospital

• 10 terabytes: Printed collection of the U. S. Library of Congress

• 500 terabytes: All the information in all the books ever written

• 24 petabytes: Google’s daily processing

• 500 exabytes: The world’s total digital content (as of May 2009).

Prefix Scale

K (kilo) Thousand

M (mega) Million

G (giga) Billion

T (tera) Trillion

P (peta) Quadrillion

E (exa) Quintillion

Z (zetta) Sextillion

Y (yotta) Septillion

Big Picture (Computer Hardware)

Big Picture (Computer Hardware)