Transcript Chapter05

Chapter 5
Computing Components
The (META) BIG IDEA
Cool, idea but maybe too big 
• DATA
– Must be stored somewhere in a storage device
• PROCESSING
– Data must be moved around and manipulated
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Chapter Goals
• Components of a von Neumann machine
• Von Neumann fetch-decode-execute cycle
– What does “running a program” mean, anyway?
• Limitations of von Neumann architecture
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Chapter Goals
• Memory “Pyramid”
– Memory has characteristics and trandoffs
– Primary vs Secondary memory
• Primary memory organization (RAM)
• Secondary memory (auxiliary storage devices)
• Alternatives to von Neumann architecture
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Computer Components
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Motherboard
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WHAT A MESS!!!
We need to
ABSTRACT
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We need Some Abstraction!!!
• Real hardware is messy
• Especially Intel architecture because of
backward compatibility (aka legacy issues)
• We need some simpler models (abstractions)
of von Neumann architecture
Who has been to
Disneyland?
Von Nuemann Architecture
• The parts are connected to one another by a
collection of wires called a bus
Figure 5.2 Data flow through a von Neumann architecture
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Von Nuemann Architecture
• The bus is SHARED by several devices
• This affects how data flows
• ANALOGY:
– Who do you call most on your cell phone?
– Some devices communicate more than others
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von Neumann Architecture
Figure 5.1 The von Neumann architecture
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Main Memory (RAM)
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RAM
• Memory is a
collection of cells,
each with a unique
physical address
• How many data
bits?
• How many address
bits?
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What is in a CPU??
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CPU Components
• Arithmetic Logic Unit
• Control Unit
• Registers
CPU
MEMORY
program
CU
REG
(holds data)
(The Boss)
ALU
(does the work)
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Arithmetic/Logic Unit
• Performs basic arithmetic operations:
– Adding
– Multiplying
– Dividing
• Performs logical operations such as AND, OR,
and NOT
– Example: RGB color mixing
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Registers
• Contain the data that the CPU is processing
“at the moment”
• There is a set of registers
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Control Unit
• Control unit controls the instruction cycle
• Reads in a SW program, one instruction at a
time
• Tells the ALU what to do
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Control Unit
• There are two special registers in the control
unit
– The instruction register (IR) contains the
instruction that is being executed
– The program counter (PC) contains the address of
the next instruction to be executed
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The Fetch-Execute Cycle
The Control Unit makes the CPU go through the
following cycle:
1) Fetch the next instruction
2) Decode the instruction
3) Execute the instruction
– the cycle repeats – forever!
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Fetch-Decode-Execute Cycle
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Memory Mixes
• Computers contain a mix of different kinds of
memory
• Why????
• Will it always be this way?
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Memory and the Memory Pyramid
Cache
Capacity
Main RAM
Cost
&
Speed
Flash RAM
Magnetic Disk
Tape
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Primary and Secondary Storage
• Primary Storage
–
–
–
–
aka “Main Memory” (usually RAM)
the “working memory” of the CPU
Fast
High $ per byte
• Secondary Storage
– where all the stuff that is not being worked on “now” is stored (usually
DISK)
– Slow
– Low $ per byte
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Primary Memory - RAM
• RAM stands for Random Access Memory
– Any location can be accessed quickly,
– Same amount of time to access any location (aka ‘random’)
• RAM is volatile
– Data is LOST when the power is turned off
• Primary (Main) memory is
– Volatile
– Limited
– Expensive
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Primary vs Secondary
• Computers have a BALANCE of Primary and
Secondary Memory
• Trade offs:
– Speed
– Size
– Cost
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Secondary Memory
• Secondary memory is
– Big
– Cheap
– Slower than Primary Memory
• Examples:
– Magnetic Disk
– CD Rom
– Flash (Solid State Drives)
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Magnetic Tape
• The first truly mass
auxiliary storage
device was the
magnetic tape drive
• Cassette Tapes are
still used for large
data backups
Figure 5.4 A magnetic tape
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Magnetic Disks
• A read/write head travels across a spinning magnetic
disk, retrieving or recording data
Figure 5.5
The organization
of a magnetic disk
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Compact Disks
• A CD drive uses a laser to read information
stored optically on a plastic disk
• CD-ROM is Read-Only Memory
– Approximately 700MB
• DVD stands for Digital Video Disk
– Approximately 4 GB
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QUESTION TIME
• Does the PERFECT MEMORY EXIST??
• What would be its characteristics??
Does anybody have a Solid State Drive
(SSD) ??
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Von BOTTLENECK
• Von Neumann has a fundamental limitation:
•The SHARED BUS!!
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Alternatives to von Neumann
• Several alternative architectures exist
• Some are used to enhance von Neumann
• Examples:
– Synchronous Processing (Parallel)
– Pipelining (Serial)
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Synchronous processing
• One approach to parallelism is to have multiple processors
apply the same program to multiple data sets
Figure 5.7 Processors in a synchronous computing environment
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Some Parallel Architecture Examples
• Google
– Many servers in one building (“Server Farm”)
• SETI
– Geographically Distributed Processors
• Quad Core and Tilera
– Several CPUs on one chip
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Pipelining
• Arranges processors in tandem, where each
processor contributes one part to an overall
computation
Figure 5.8 Processors in a pipeline
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Pipelining Examples
• Like a manufacturing assembly line (cars)
• Some series of tasks can be pipelined
– Example: game video processing
1. Build vector model
2. Wrap vectors in bitmaps
3. Generate camera view
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