comp 4—power tools for the mind 1 what’s in the box? 1 memory and storage –primary...

COMP 4—Power Tools for the Mind 1What’s in the box?

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Memory and Storage

–Primary• Organization• Types• Attributes

–Auxiliary (Secondary)• Types• Technology

What we’ll cover for this lecture topic:


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Computers basically have two-level storage:

ProcessorCU ALU

Inputs

Storage

MemoryRAM ROM

Outputs

Primary storage: MEMORY (chips)

Secondary/Auxiliary storage: STORAGE (disks…)


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– 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/transformation 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 don’t want to slow down the processor. Therefore we use electronic storage (rather than electromechanical).

Primary Memory


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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).


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– 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?

Arrangement (similar to P.O. boxes):

– MEMORY: Holds INSTRUCTIONS & DATA that we are interested in processing NOW.

# 0000 0000

# 0000 0001

0 1 0 1 0 0 1 1

# 0000 0010

1 0 0 1 1 0 0 1

# 0000 0011

1 1 1 1 0 0 0 00 1 1 0 0 1 0 1

1 1 0 0 1 1 0 0

# 0000 0100

......


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0 1 0 1 0 0 1 0 1

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

spreadsheet’s absolute cell reference (e.g. $B$24).– 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 AADD A 1STORE A #0000 0011 0 1 0 1 0 0 1 0

# 0000 0011

memoryRegister A

CPU

_ _ _ _ _ _ _ _ 1


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– 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.


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– UNLIKE a spreadsheet cell, a single memory cell can hold much less: 8 bits

– Cannot address bits individually (grouped by 8)

#0000 00010 1 0 0 0 0 0 1

One memory cell:


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• 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)?

Interesting digression# 0000 00010 1 0 0 0 0 0 1


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– 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 numberIntegers: 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.


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Logical structure of 1 memory cell: 8 bitsPhysical structure of 1 memory cell: 8 capacitors

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)

• Total primary memory and auxiliary storage in one’s 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 trillion240


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– RAM: Random Access Memory• RAM is fast.

– Virtually no speed penalty for accessing bits, no matter which cell they’re in: “Random access”

• RAM is writable (by the user). (launch; load; edit…)

• RAM is volatile.

• Stores what’s 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)

Types of primary memory


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– ROM (read-only memory)• Contents pre-written and permanent: non-volatile.• Typically small: <1 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?

“Virtual Memory”• Textbook has a good explanation of this process so I won’t

cover it much here. Just understand the basic idea behind it.

Just for culture: • Other flavors of nonvolatile primary memory: PROM; EPROM;

EEPROM• Flash Drives• CMOS (battery-powered; see text for more info)

use disk space to simulate RAM


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ProcessorCU ALU

Inputs

Storage

MemoryRAM ROM

Outputs


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– 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.

Auxiliary Storage

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)


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• 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

MAGNETIC Storage


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The resulting magnetic field can be in one of two different orientations (polarities):

North-South(clockwise)

South-North (counter-clockwise)

A moving electrical charge (current) creates a magnetic field...

depending on the

direction thatthe current

flows

How a magnetic recording works

“INDUCTION”


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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.


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A moving magnetic field creates an electric field...

So: if there’s 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.


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• Ribbon coated with iron oxide

• Reel-to-reel (old mainframes)

• Cassettes, cartridges

• Sequential Access storage device:– to reach data written at the end

need to go through all other data

• Generally used for:

– short-term backup

– transport

Magnetic tape011101000

Tap

e h

ead

TA

PE


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Magnetic disks• Surface divided into wedges:

sectors.• Bits are stored within a sector

along concentric circles called tracks. (Floppy disk: ~80 tracks)

• 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 that’s so?– DIGRESSION: Speed…. SEEK time, SPIN

rate

Sec 0

Sec 1

Sec 2

Track 0

Sec 3

Sec 4

Sec 5

Sec 6Track 1

Track 2


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• 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


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– 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?


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• Hard disks/disk drives (fixed)

– Rigid aluminum or glass; various sizes; >1 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


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Digression: What’s a head crash?– Very fast spin rates.

• R/W head floats above hard disk surface on tiny cushion of air……..


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– High data density: smaller recorded bits.

Digression: What’s a head crash?– Very fast spin rates.

• R/W head floats above hard disk surface on tiny cushion of air.

– Challenge: decrease head’s “flying height” to increase signal’s amplitude (so it’s 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


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• 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


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• 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.

OPTICAL Storage

QUOTABLE


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CD-ROM [standard; early generations]

Many flavors …READ ONLY:

• 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 what’s on it!

• Read only; who writes?

• Good for? Games, Software, Reference materials, Library materials, for being AOLnoyed, …

manufacturer


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RECORDABLES: Recordable by: USER (various technologies) readable by most standard, same-sized drives and players.

WRITE ONCE: CD-R Good for? (used where data won’t 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


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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


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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…..


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– DVD-RAM, DVD-RW, DVD+RW (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 DVD+RW and

DVD-RW.

• Generally “downward” compatible.

• Becoming popular for backups as prices come down.

– About 8X the storage capacity of a CD


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So what?– DVD: Can store a whopping 2.6 to 8.75 GB!

• For huge graphics files, video, etc

http://www.computershopper.comhttp://www.cnet.com … (lots!)

http://www.adaptec.com

For desktop or notebooks:– Getting popular: DVD+-RW/CD-RW combo drive

• Again, be aware of writability and compatibility issues.

comp 4—power tools for the mind 1 what’s in the box? 1 memory and storage –primary...

Documents

memory cell address

memory address

primary memory slide

memory location

spreadsheet cell

cell contents

power tools

electronic storage