04/13/23 1

Data Storage

CSci 131Sept. 12, 2006

04/13/23 2

Outline

Bytes Main Memory Mass Storage Comparison Quiz1 – 10 min

04/13/23 3

Bit Review Flip-flops and capacitors provide means

for storing a bit Flash memory – electrons are trapped

inside tiny chambers Two states are full or empty chambers

Flip flops, cores, capacitors are forms of dynamic memory

Flash memory holds the data “permanently”

04/13/23 4

Bytes Byte is 8 ordered bits

10000000 and 00000001 are different The left end is the high-order end and the

leftmost bit is the most significant bit The right end is the low-order end and the

rightmost bit is the least significant bit

04/13/23 5

Storage Measurements

04/13/23 6

Example

A file is 5,376,000 bytes long How many kilobytes (KB) is this?

How many megabytes (MB) is this?

04/13/23 7

Main Memory Main memory is a sequence of cells

that can hold 1 byte Each cell has a unique numerical

address Main memory is ordered

04/13/23 8

Main memory Consecutive bytes (cells) are used for

larger data

04/13/23 9

Properties of main memory Random Access Memory – RAM

each cell or memory location can be referenced, accessed, or modified in the same amount of time

Memory is very fast Access time is measured in

nanoseconds Memory is volatile

Contents disappear when power is gone

04/13/23 10

Mass Storage

Also called Secondary Memory Much larger and cheaper than RAM Data contents remain after power is

disconnected Access times are slower (in

milliseconds) since secondary storage relies on mechanical motion

04/13/23 11

Types of Mass Storage

Hard disk Floppy disk Zip Disk CD DVD Flash drive

04/13/23 12

Disk Storage Each surface of a disk has magnetic

coating The surface is divided into rings called

tracks Each track is broken down into

sectors Every track on a disk has the same

number of sectors Each sector holds the same amount of

data

04/13/23 13

Disk Storage

04/13/23 14

Disk Storage

Disk spins while a read/write head moves in and out to view different areas

Types: Hard disks: not removable, fast,

primary storage Floppy/Zip disks: removable, slower,

used for distribution or backup

04/13/23 15

Disk Access

Move read/write head to proper track

Wait for disk to spin and sector to move under read/write head

Read from (write to) the sector as it passes under the read/write head

04/13/23 16

Disk Access Terms

Seek time: time to move read/write head between tracks

Latency time: time for ½ disk rotation

Access time: seek time + latency time

Transfer rate: rate at which data can be transferred to/from disk

04/13/23 17

Compact Disc (CD) Uses optical technology instead of

magnetic discs Each CD is a spinning, 5 in. diameter

disc with reflective material and protective coating

Writing requires a laser creating variations on the surface

Reading uses a laser and mirrors to monitor the surface of the CD

04/13/23 18

Compact Disc (CD)

CD is a single track that spirals where a hard drive was multi-track

All sectors are the same size Benefit of better storage space use Drawback of slower access time

Main types: CD-ROM, CD-R, CD-RW, DVD

04/13/23 19

Tape Storage Long plastic band with magnetic

coating Organized into blocks separated by

inter-record gaps Blocks store data Inter-record gaps help seeking

04/13/23 20

Tape Storage Tape access is linear. Tape must be wound until needed block is

under the read/write head. Tapes are slow but can hold large amounts

of data Used primarily as backups for hard drives

04/13/23 21

Comparison

04/13/23 22

Assignment for 09/14

Read Sections 1.4, 1.5 HW1 due Thurs. 14 (next class) Quiz1 now

04/13/23 23

Main Memory

Want as much fast storage as possible But RAM is volatile Disk slower but larger and non-volatile Cost Engineering Why 1GB of RAM? 100 GB hard-drive?