Introduction to Computer Architecture

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Introduction to Computer Architecture
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Introduction to Computer Architecture

• Architecture and Organization
• Architecture is those attributes visible to the
  programmer
• Instruction set, number of bits used for data
  representation, I/O mechanisms, addressing
  techniques.
• e.g. Is there a multiply instruction?
• for example, MULU/MULS in Motorola 68000
• Organization is how features are implemented
• Control signals, interfaces, memory technology.
• e.g. Is there a hardware multiply unit or is it
  done by repeated addition?

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Introduction to Computer Architecture

• Architecture and Organization (contd)
• All Intel x86 family share the same basic
  architecture
• The IBM System/370 family share the same basic
  architecture
• This gives code compatibility
• At least backwards
• Organization differs between different versions

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Introduction to Computer Architecture

• Rapidly changing field
• vacuum tube ? transistor ? IC ? VLSI
• doubling every 1.5 years memory capacity
  (Moores Law) processor speed (Due to
  advances in technology and organization)
• Why learn this stuff?
• you want to call yourself a computer scientist
• you want to build software people use (need
  performance)
• you need to make a purchasing decision or offer
  expert advice

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Hardware and Software

• Components
• input (mouse, keyboard)
• output (display, printer)
• memory (disk drives, DRAM, SRAM, CD)
• Central processing unit (CPU)
• network
• components connected by bus

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Hardware Components

• Main Memory
• Where the instructions and local data for a
  program reside while a program is executed
• Composed of bits which are grouped into into
  addressable units of bytes
• Bytes are in turn paired into words which can be
  treated as single storage/transfer units

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Hardware Components

• Main Memory (contd)
• Implementation
• Core
• Semiconductor
• Core (1950s and 1960s)
• consists of loops of a magnetic material
• two magnetized directions represent 1 and 0
• non-volatile
• fast, expensive, bulky
• destructive read
• reading a core erased data stored in it
• necessary to restore the data as soon as it had
  been extracted

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Hardware Components

• Main Memory (contd)
• Semiconductor (1970 -)
• integrated-circuit technology
• first semiconductor memory
• -- 1970
• -- 256 bits on one chip
• -- about the size of a core, faster, but
  cost is higher
• -- nondestructive read
• milestone in 1974
• cost per bit of semiconductor lt cost per bit of
  core
• Generations (every three years) 1K, 4K, 16K,
  64K, 256K, 1M, 4M, 16M bits, ... on a single chip
  -- Moores Law

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Hardware Components

• Main Memory (contd)
• Volatility
• Non-volatile Memory information still retained
  after power off
• e.g., ROM (Read-Only Memory)
• Volatile Memory information not retained when
  power off
• e.g., RAM (Random-Access Memory)

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Hardware Components

• Main Memory (contd)
• Parity
• Number of bits set in a byte
• Error detection
• Can be either even or odd
• Example
• Odd parity is used,
• a byte 01001011 is to be written to main
  memory
• ? parity bit is set to 1
• When the byte is retrieved, suppose there
  is an error, so the byte
• became 01101011, now the number of set
  bits is 5, parity bit is 1,
• 51 6 is even ? an error
• Other storage devices such as tape and disk also
  use parity checking
• Hamming code
• Error correction

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Hardware Components

• Disks
• Composed of one or more platters

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Disk Structure
Spindle
R/W Head (1 per surface)
Surface7
Platters
Tracks
Platter
Track0
Sectors
Track
Surface1
Actuator
Surface0
Cylinder
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Hardware Components

• Disks
• Address of a block of data on a disk (Cylinder,
  Track, Sector)
• To access a block of data Seek, Rotate, Transfer
• seek position head over the proper track
  (8 to 20 ms. avg.) rotational latency wait
  for desired sector transfer grab the data
  (one or more sectors) 2 to 15 MB/sec
• Access time seek time rotational latency
  data transfer time
• Example A disk has an average seek time 12ms,
  rotational latency 5.6 ms, and transfer rate
  5MB/sec. What is the average time to read a
  block of 512 byte sector?

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Hardware Components

• CPU
• ALU (Arithmetic and Logic Unit)
• The component which
• - actually performs arithmetic and logical
  operations
• - governs flow of a program
• Constructed by electronic circuits
• Control Unit, responsible for
• reading an instruction
• determining what operation
• determining addresses of operands
• then instructing ALU to perform operation
• Control process can be hardwired or using
  micro-programming (similar to RTL) to implement
  instruction set of a computer

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Instruction Set Architecture

• A very important abstraction
• interface between hardware and low-level software
• standardizes instructions, machine language bit
  patterns, etc.
• allows computer designers to separate functions
  from hardware
• advantage different implementations of the same
  architecture
• disadvantage sometimes prevents using new
  innovations
• Modern instruction set architectures
• 80x86/Pentium/K6, PowerPC, DEC Alpha, MIPS,
  SPARC, HP