CIS 141 LectureStorage Hardware (saving data/information)

Thad CrewsWestern 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 HierarchyCPU

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

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.

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”.

Optical DiscsHow does a laser read data on an optical disc?

laserdiode

laserdiode

prism prismlight-

sensingdiode

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

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 ScaleK (kilo) Thousand

M (mega) MillionG (giga) BillionT (tera) TrillionP (peta) QuadrillionE (exa) Quintillion

Z (zetta) SextillionY (yotta) Septillion

Big Picture (Computer Hardware)

Big Picture (Computer Hardware)