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Auxiliary Storage,

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Medium: tape (reel or cartridge) on a disk, whose R/W head moves over it as it spins. ... Cassettes, cartridges. Sequential Access storage device: to reach ... – PowerPoint PPT presentation

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Title: Auxiliary Storage,


1
Memory and Storage
What well cover for this lecture topic
  • Primary
  • Organization
  • Types
  • Attributes
  • Auxiliary (Secondary)
  • Types
  • Technology

2
Computers basically have two-level storage
Primary storage MEMORY (chips)
Secondary/Auxiliary storage STORAGE (disks)
Processor
CU ALU
Outputs
Inputs
Memory
RAM ROM
Storage
3
Primary Memory
  • Functional unit for storing retrieving all 5
    kinds of information -- used by the processor.
  • electronic storage no moving parts (?
    fast!!!!)
  • For every transformation
  • The processor must fetch a basic instruction, one
    at a time, and copy it to its own special storage
    registers before it can do any operation/transform
    ation on data.
  • The processor also has to copy the data into its
    own special storage registers (? more about the
    actual process later).
  • The processor is also electronic and very FAST
    !!!
  • We dont want to slow down the processor.
    Therefore we use electronic storage (rather than
    electromechanical).

4
  • Digression a basic machine language statement
  • OP CODE part of machine code (a bunch of bits)
    that tells the CPU which operation to perform
    (add, multiply, compare, ...)
  • OPERAND also part of the machine code (another
    bunch of bits) that tells the CPU at which memory
    address the data is stored that is should operate
    on.

You will see a lot on about this soon when we
study the architecture of the CPU and how it
operates on data (e.g. transforms data).
5
  • MEMORY Holds INSTRUCTIONS DATA that we are
    interested in processing NOW.

Arrangement (similar to P.O. boxes)
  • Each is called a memory cell or a memory
    location.
  • Each cell is identified by aunique binary
    address.
  • Each cell contains a certain number of bits
    (usually eight).
  • Similar to what in a spreadsheet?
  • Why is uniqueness important?

6
Memory addressing
  • Just as Excel uses a cell reference in a formula
    to locate a cell and to read the data stored in
    that cell, a program uses a memory address.
  • So a memory cell address is similar to a
    spreadsheets absolute cell reference (e.g.
    B24).
  • The cell contents can change, but the cell
    address or reference to the cell is always the
    same.
  • A program can write to and read from a memory
    cell through their address.

LOAD 0000 0011 A
ADD A 1
0 1 0 1 0 0 1 0
1
1
STORE A 0000 0011
7
  • What happens to data when we write or read?
  • What happens when you type (write) something into
    a spreadsheet cell that already contained some
    data?
  • Writing destroys what was stored there.
  • What happens if an Excel formula reads a data
    value from another cell
  • Reading does not destroy what is stored there.
    It just hand-over a copy.
  • 32-bit memory-addressing means that the
    computer uses memory addresses that are 32 bits
    long
  • the address bus are the wires that carry bits
    between the CPU and the memory
  • a 32-bit bus carries 32 bits at a time

232 ? 4 GB (billion) different addressable memory
cells.
8
  • UNLIKE a spreadsheet cell, a single memory cell
    can hold much less 8 bits
  • Cannot address bits individually (grouped by 8)

9
0000 0001
Interesting digression
0 1 0 0 0 0 0 1
  • How many memory cells are required to hold one
    ASCII character?
  • How many cells required to hold a bit pattern
    that can represent a single pixel with a 24-bit
    color?
  • How many cells required to hold an standard
    precision integer (which requires 32 bits)?
  • How many cells required to hold an high precision
    real number (which requires 64 bits)?
  • And.what is the term for 8 bits (which happens
    to fit perfectly into one memory cell)?

10
  • So, each memory cell (location) can hold 8 bits,
    or one byte.
  • Those 8 bits, in turn, could represent, at a
    given time
  • Part of an integer or real number
  • Integers typically 32 bits Real either
    32 or 64 bits
  • The bit pattern for one alphanumeric character
    (one character byte)
  • Part of a bit pattern for a sound sample.
  • The bit pattern for one pixel with 8-bit color.
  • 1/3rd of a bit pattern for one pixel with
    24-bit color.
  • A part of an instruction.

11
What did we say keeps track of what kind of
information a bit pattern (in memory) is
representing at a given moment?
the program (e.g. software)
Logical structure of 1 memory cell 8
bits Physical structure of 1 memory cell 8
capacitors
  • Total primary memory and auxiliary storage in
    ones computer is measured in bytes.
  • Kilobyte (KB or K) 1 thousand 210
  • Megabyte (MB) 1 million 220
  • Gigabyte (GB) 1 billion 230
  • Terabyte (TB) 1 trillion 240

12
Types of primary memory
  • RAM Random Access Memory
  • RAM is fast.
  • Virtually no speed penalty for accessing bits, no
    matter which cell theyre in Random access
  • RAM is writable (by the user). (launch load
    edit)
  • RAM is volatile.
  • Stores whats being used now Mostly determined
    by whom? Often called user memory --
  • Typically 256 or 512 MB (and up) for personal
    computers.
  • Advice Buy as much as you can afford.
  • Affects overall speed of system (page faults,
    caching)

13
  • ROM (read-only memory)
  • Contents pre-written and permanent
    non-volatile.
  • Typically small lt1 MB
  • Stores bootstrap program.
  • Stores BIOS (very basic parts of the operating
    system that rarely change are hardwired in ROM)
  • Often called Firmware. Why do you suppose?
  • Just for culture
  • Other flavors of nonvolatile primary memory
    PROM EPROM EEPROM
  • Flash Drives
  • CMOS (battery-powered see text for more info)
  • Virtual Memory
  • Textbook has a good explanation of this process
    so I wont cover it much here. Just understand
    the basic idea behind it.

? use disk space to simulate RAM
14
Processor
CU ALU
Outputs
Inputs
Memory
RAM ROM
Storage
15
Auxiliary Storage
  • Want more memory than is affordable in
    electronic memory.
  • Cheaper shares one set of electronics for R and
    W (the head).
  • But much slower at least by 10,000 times.
  • Physically moves medium past R/W mechanism.
  • Need non-volatile storage that is recordable.
  • Primary memory like your
    closet
  • Access is frequent and fast but less is taken at
    a time (4 - 8 bytes).
  • Secondary storage like your attic
  • Access is less frequent and much slower but a
    whole block of data is taken at a time.
    (256 - 1024 bytes)

16
MAGNETIC Storage
  • Most common form of storage.
  • Magnetized spots on a surface, which may be
  • on a tape, which itself moves past a R/W head
    (like audio tape)
  • Device tape drive or unit
  • Medium tape (reel or cartridge)
  • on a disk, whose R/W head moves over it as it
    spins.
  • A disk may be floppy or rigid
  • A disk may be fixed permanently in the drive or
    removable.
  • Device disk drive
  • Medium disk

17
How a magnetic recording works
A moving electrical charge (current) creates a
magnetic field...
The resulting magnetic field can be in one of two
different orientations (polarities)
depending on the direction that the current flows
INDUCTION
18
So we can send a current through a wire (the
R/W mechanism) to magnetize a spot on an iron
surface nearby.
The spot (with magnetic field around it) will
have one of two orientations. This way the head
records (writes) physical representations of
0s and 1s on the iron surface.
19
A moving magnetic field creates an electric
field...
So if theres a wire coil nearby, the current
is sent through it in one of two different
directions
The READ head interprets the direction of the
incoming current as a 0 or a 1.
20
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21
Magnetic tape
  • Ribbon coated with iron oxide
  • Reel-to-reel (old mainframes)
  • Cassettes, cartridges
  • Sequential Access storage device
  • to reach data written at the endneed to go
    through all other data
  • Generally used for
  • short-term backup
  • transport

22
Magnetic disks
Track 0
Sec 6
Track 1
  • Surface divided into wedges sectors.
  • Bits are stored within a sector along concentric
    circles called tracks. (Floppy disk 80
    tracks)

Track 2
Sec 5
Sec 0
Sec 4
Sec 1
Sec 2
Sec 3
  • All disk drives are DASDs
  • Direct Access Storage Devices
  • File is accessed directly by giving the address
    of each block on the disk that contains the file.
  • Similar to random access except it has speed
    penalties. Why do you think thats so?
  • DIGRESSION Speed. SEEK time, SPIN rate

23
  • Floppy disks (diskette) and drives
  • Transportable storage.
  • Good to back-up a few files.
  • Digression Would you recommend backing up
    data from an entire hard drive on standard floppy
    disks? Why or why not? What could you backup?
  • Flexible plastic mylar removable media
  • Slow spin rates (360 to 400 rpm)
  • Slow seek time (300 ms)
  • R/W heads touch disk surface
  • Cheap, abundant, portable

24
  • Have gotten smaller, cheaper, higher density
  • outdated 8 (20 KB)
  • old 5.25 (140 KB 1.2 MB)
  • low density 3.5 720 KB
  • high density 3.5 1.44 MB most popular
  • SuperDisk 3.5 120, 144, and 200 MB
  • Write protect window what for?
  • Any special care for disks?
  • Do floppy disks ever fail?

25
  • Hard disks/disk drives (fixed)
  • Rigid aluminum or glass various sizes gt1
    platter
  • Much faster spin rates (currently up to 10,000
    rpm)
  • Much faster access speeds (seek time 5 15 ms)
  • Much faster transfer rates (15 MB/sec and up)
  • Fixed means media NOT removable from the
    hardware
  • Internal and external
  • Capacities
  • for older PC systems 20 MB...80 MB...200 MB
  • Today 20-500 GB and up

26
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27
  • Digression Whats a head crash?
  • Very fast spin rates.
  • R/W head floats above hard disk surface on tiny
    cushion of air..

28
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29
  • Digression Whats a head crash?
  • Very fast spin rates.
  • R/W head floats above hard disk surface on tiny
    cushion of air.
  • High data density smaller recorded bits.
  • Challenge decrease heads flying height to
    increase signals amplitude (so its detectable)
  • R/W head can crash into contaminant on disk
    surface, then onto disk!

So disks permanently sealed in case, fixed in
drive Winchester technology
30
  • Removable disk storage
  • Great for backups
  • Very transportable
  • Internal external
  • many flavors
  • watch for compatibility issues.
  • A few choices (actual numbers just for culture---
    try to get a sense of how much more they store
    than a standard removable floppy disk).
    Examples
  • ZIP 250 MB Zip Drive - w/5 disks
    75
  • JAZ 2 GB Iomega JAZ External
    300
  • Syquest 1.5 GB 300 (been around longer)
  • Flash Drives

31
OPTICAL Storage
  • Use lasers to record (write), and also to read.
  • Record high-powered laser burns pits into
    reflective coating.
  • Read weaker laser reads pits differences in
    reflectance of pits lands interpreted as 0 and
    1. (See textbook figures)
  • For PCs 650 MB per CD-ROM (275,000 pgs of
    text)
  • Similar to audio CDs, but more error-correction.
  • Internal external drives.

32
Many flavors
READ ONLY
  • CD-ROM standard early generations
  • Rigid platter various sizes, densities.
  • Single SPIRAL track (starts near center ?
    outward)
  • Usually 650 MB, about 4 ¾
  • Standard transfer rate was 150 Kb/sec but soon
    there came 2x 4x 24x 40x ?
  • Biggest Source of ERROR dust
  • Disk cost depends on whats on it!

manufacturer
  • Read only who writes?
  • Good for? Games, Software, Reference materials,
    Library materials, for being AOLnoyed,

33
  • RECORDABLES
  • Recordable by USER (various technologies)
  • readable by most standard, same-sized drives
    and players.
  • WRITE ONCE CD-R
  • Good for? (used where data wont change)
  • Multimedia presentations archives greatest
    hits photos video clips
  • Hold 650 MB of data, or 74 min. of audio
  • Can copy files to it (like removable magnetic
    media) but a little more complicated (software
    comes with drive)

Unalterable once written
34
  • WRITE MANY CD-RW
  • Recordable/writable many times (when used with
    appropriate software)
  • RW Drives generally can record on both CD-R or
    CD-RW disks.
  • Getting very popular
  • Often used for backups
  • somewhat more expensive 700-MB CDs that can be
    read by most CD-ROM drives
  • compatibility issues

35
  • Newer optical disc technology DVD
  • Digital video (versatile) disc
  • Similar to DVD-video that you hook up to your
    TV.
  • READ ONLY
  • DVD-ROM instead, holds computer data is
    hooked to your computer..
  • RECORDABLE VERSIONS
  • DVD-R (write once)
  • and..

36
  • DVD-RAM, DVD-RW, DVDRW (write many)
  • A standards problem different formats--which
    drives can read and write to which
    formats.confusing for customers.
  • . There are several types of DVD drives, and at
    least four versions of media, none of which is
    completely compatible with the other. from
    keynote addressed delivered at Intel Developer
    Forum week of 9 Sept 2002.
  • New drives can read and write to both DVDRW and
    DVD-RW.
  • Generally downward compatible.
  • Becoming popular for backups as prices come down.
  • About 8X the storage capacity of a CD

37
  • So what?
  • DVD Can store a whopping 2.6 to 8.75 GB!
  • For huge graphics files, video, etc
  • For desktop or notebooks
  • Getting popular DVD-RW/CD-RW combo drive
  • Again, be aware of writability and compatibility
    issues.

http//www.computershopper.com http//www.cnet.com
(lots!) http//www.adaptec.com
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