Post on 02-Jun-2015
DATA STORAGE
Chapter 1
1.1 BITS AND THEIR STORAGE
Data Storage1-2
BITS AND BIT PATTERNS
Bit: Binary Digit (0 or 1)
Bit Patterns are used to represent
information. Numbers
Text characters
Images
Sound
And others
1-3
BOOLEAN OPERATIONS
Boolean Operation: An operation that manipulates
one or more true/false values
Specific operations
AND
OR
XOR (exclusive or)
NOT
1-4
THE BOOLEAN OPERATIONS AND, OR, AND XOR
(EXCLUSIVE OR)
1-5
GATES
Gate: A device that computes a Boolean operation
Often implemented as (small) electronic circuits
Provide the building blocks from which computers are
constructed
VLSI (Very Large Scale Integration)
1-6
A PICTORIAL REPRESENTATION OF AND, OR, XOR, AND NOT
GATES AS WELL AS THEIR INPUT AND OUTPUT VALUES
1-7
FLIP-FLOPS
Flip-flop: A circuit built from gates that can store one bit.
One input line is used to set its stored value to 1
One input line is used to set its stored value to 0
While both input lines are 0, the most recently stored value is
preserved
1-8
A SIMPLE FLIP-FLOP CIRCUIT
1-9
1.2 MAIN MEMORY
Data Storage1-10
MAIN MEMORY CELLS
Cell: A unit of main memory (typically 8 bits
which is one byte) Most significant bit: the bit at the left (high-order) end
of the conceptual row of bits in a memory cell
Least significant bit: the bit at the right (low-order) end
of the conceptual row of bits in a memory cell
1-11
THE ORGANIZATION OF A BYTE-SIZE MEMORY CELL
1-12
MAIN MEMORY ADDRESSES
Address: A “name” that uniquely identifies
one cell in the computer’s main memory The names are actually numbers.
These numbers are assigned consecutively starting at
zero.
Numbering the cells in this manner associates an order
with the memory cells.
1-13
MEMORY CELLS ARRANGED BY ADDRESS
1-14
MEASURING MEMORY CAPACITY
Kilobyte: 210 bytes = 1024 bytes Example: 3 KB = 3 times1024 bytes
Sometimes “kibi” rather than “kilo”
Megabyte: 220 bytes = 1,048,576 bytes Example: 3 MB = 3 times 1,048,576 bytes
Sometimes “megi” rather than “mega”
Gigabyte: 230 bytes = 1,073,741,824 bytes Example: 3 GB = 3 times 1,073,741,824 bytes
Sometimes “gigi” rather than “giga”
1-15
1.3 MASS STORAGE
Data Storage1-16
MASS STORAGE
On-line versus off-line
Typically larger than main memory
Typically less volatile than main memory
Typically slower than main memory
1-17
MASS STORAGE SYSTEMS
Magnetic Systems
Disk
Tape (all but obsolete)
Optical Systems
CD
DVD
Blu-Ray
Flash Drives
Solid State Drives (SSDs)
1-18
MAGNETIC DISKS
1-19
GAP BETWEEN HEAD AND PLATTER
1-20
Head
Smoke
Particle
Human
Hair
Dust
Particle
DISK PERFORMANCE
1-21
Disk Performance
Seek time
Rotational latency
Transfer rate
OPTICAL DISKS
1-22
CD AND DVD TRACK COMPARISON
1-23
CD DVD
FILES
A file is a named collection of bits
Files are often stored in pieces
1 byte chunks in memory
Sector-sized chunks on disk
1-24
1.4 REPRESENTING INFORMATION AS BIT
PATTERNS
Data Storage1-26
REPRESENTING TEXT
Each character (letter, punctuation, etc.) is
assigned a unique bit pattern
ASCII
American Standard Code for Information Interchange
Uses patterns of 7-bits to represent most symbols used in
written English text
128 (27) unique characters
Unicode
Uses patterns of 16-bits to represent the major symbols used
in languages world side
65,536 (216) possible characters
ISO
International Organization for Standardization
4,294,967,296 (232) possible characters
1-27
“HELLO.” IN ASCII
1-28
REPRESENTING NUMERIC VALUES
Binary: a number system using only the digits 0 (zero) and 1 (one)
Maps well to the internal characteristics of the computer
Limitations of computer representations of numeric values
Overflow: happens when a value is too big to be represented
Truncation: happens when a value is between two representable values
1-32
REPRESENTING IMAGES
1-33
Bit map techniques
Pixel: short for “picture element”
RGB
Luminance and chrominance
Vector techniques
Scalable
TrueType and PostScript
SCALABLE VS. BITMAPPED FONTS
1-34
A SOUND WAVE REPRESENTED BY THE SEQUENCE 0,
1.5, 2.0, 1.5, 2.0, 3.0, 4.0, 3.0, 0
1-35
1.5 THE BINARY SYSTEM
Data Storage1-36
THE BASE TEN AND BINARY SYSTEMS
1-37
DECODING THE BINARY REPRESENTATION 100101
1-38
FINDING THE BINARY REPRESENTATION OF 13
1-39
BINARY ADDITION
1-40
DECODING THE BINARY REPRESENTATION 101.101
1-41
1-42
There are 10 kinds of people in
the world: those who understand
binary and those who don’t.
HEXADECIMAL NOTATION
Hexadecimal notation: A shorthand notation for long bit patterns
Divides a pattern into groups of four bits each
Represents each group by a single symbol
Example: 1010 0011 becomes A3
1-43
THE HEXADECIMAL CODING SYSTEM
1-44
1-45
How many people can read hex
if only you and DEAD people
can read hex? 57,006
1.6 STORING INTEGERS
Data Storage1-46
STORING INTEGERS
Two’s complement notation: The most popular
means of representing integer values
Excess notation: Another means of representing
integer values
Both can suffer from overflow errors.
1-47
TWO’S COMPLEMENT
1-48
Fixed number of bits
MSB is sign bit
1 = negative
0 = positive
ENCODING IN TWO’S COMPLEMENT NOTATION
1-49
ADDITION AND SUBTRACTION USING TWO’S
COMPLEMENT
1-50
TAKING ISSUE WITH THE BOOK
“The point is that computers
can make mistakes.”-J. Glenn Brookshear, Computer Science, an Overview, p. 54
1-51
WRONG
TAKING ISSUE WITH THE BOOK
Computers don’t make
mistakes. They do exactly
what you tell them to.
1-61
EXCESS NOTATION
Another system of representing signed integers
1. List all bit patterns of a given length
2. Find the first bit pattern with a 1 in the MSB; this will
represent zero
3. Patterns below our zero represent negative number,
patterns preceding it represent positive numbers
1-62
EXCESS EIGHT CONVERSION TABLE
1-63
1.7 STORING FRACTIONS
Data Storage1-64
STORING FRACTIONS
Floating-point Notation: Consists of a sign bit, a
mantissa field, and an exponent field.
Related topics include
Normalized form
Truncation errors
1-65
FLOATING-POINT NOTATION COMPONENTS
1-66
ENCODING THE VALUE 25⁄8
1-67