CIS 141 Lecture

Storage Hardware (saving data/information) Thad Crews Western Kentucky University

SAVING INFORMATION

S

TORAGE

H

ARDWARE

(Remember: Digital vs. Analog) • Digital systems have discrete values  1 / 2 / 3 / 4 / 5  On / 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 – Output INPUT PROCESS • •

CPU Memory

OUTPUT

Storage INPUT PROCESS • •

CPU Memory

This memory is

volatile

which means it requires electrical power to hold its value.

OUTPUT

Storage INPUT PROCESS • •

CPU Memory

“RAM” “Memory” “Main Memory” OUTPUT STORAGE • • • “Secondary Memory” “Storage”

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

  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

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.” Mini Memory Card

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

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.

Clearance between head and platter is approximately two-millionths of an inch Do NOT shake your machine while your hard drive is spinning.

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 Discs How does a laser read data on an optical disc?

disc label lens pit land Step 1.

Laser diode shines a light beam toward disc.

prism 0 light sensing diode Step 2.

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

laser diode laser diode prism lens 1 light sensing diode Step 3.

Reflected light is deflected to a light-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 = 1 DVD = 1 BD = 486 Floppy Disks 3,263 Floppy Disks 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 60 • th Anniversary of Tape Storage: Read more here

SUMMARY (Computer Hardware)

Ch6 Ch7 Ch7 Ch8 Quiz1

(Remember: Prefixes)

Prefix

K (kilo) M (mega) G (giga) T (tera) P (peta) E (exa) Z (zetta) Y (yotta)

Scale

Thousand Million Billion Trillion Quadrillion Quintillion Sextillion Septillion • 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).

Big Picture (Computer Hardware)

Big Picture (Computer Hardware)