Physics 413 Chapter 1

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Physics 413Chapter 1
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Computer Architecture

• What is a Digital Computer ? A computer is
  essentially a fast electronic calculating
  machine.
• What is a program ? A program is a set of very
  simple instructions that a computer can
  understand. Examples of simple instructions are
  ADD two numbers, Is X gt Y?, COPY A into the
  memory.
• What is Machine Language ? The set of
  exceedingly simple and primitive instructions
  that a computer can understand is called the
  Instruction Set or Machine Language.

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Architecture and Organization

• Computer Architecture deals with the design of
  those components of a computer that are
  accessible to a programmer. For instance, the
  Motorola 6800 does not have a MUL instruction but
  the Pentium does.
• Computer Organization deals with the
  implementation of the architecture and may be
  transparent to the programmer. For instance,
  precisely how is MUL implemented in the hardware?

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Levels of Abstraction

• L5 High-level Language (C, Java)
• L4 Assembly Language
• L3 Operating System
• L2 Instruction Set Architecture (ISA)
• L1 Microarchitecture Level
• L0 Digital Logic Level
• Transistors

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A Brief History of Computers

• First Generation - Vacuum Tubes - 1945-1955 ENIAC
  (Electronic Numerical Integrator and Computer)
  had 18,000 Vacuum Tubes, 1500 relays and weighed
  30 tons
• Second Generation - Transistors - 1955-65 - PDP
  -8 (DEC)
• Third Generation - IC - 1965-80 - IBM 360
• Fourth Generation - 1980- ? VLSI - Pentium4
  -PowerPC (G4) - SPARC

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Intel and Motorola/IBM Microprocessors

• CPU Year Data/Address Clock
  Transistors
• 4004 1971 4 / 8 108 kHz 2,300
• 8088 1979 8 / 20 8 MHz 30,000
• P4 2000 64 / 32 3 GHz 42 M
• 6800 1974 8 / 16 1 MHz 6000
• G4 1999 64 / 32 800 MHz
  10.5 M
• CISC Complex Instruction Set Computers (6800)
• RISC Reduced Instruction Set Computers (G4)
• CISC RISC ( Pentium 4 )
• EPIC Explicitly Parallel Instruction Computing
• Intel HP Itanium
  (www.dell.com)

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Moores Law

• The number of transistors on a chip doubles every
  18 months
• Example From 1992 -1995 memory chip size
  quadrupled from 16M to 64 M

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All about microprocessors

• ROM is where the program that initializes the PC
  is stored.
• RAM access is fast
• ADDRESS BUS carries the address of RAM, ROM, and
  other peripherals
• 6800 has 16 address lines, A0 through A15
• DATA BUS carries data back and forth between the
  microprocessor and RAM, ROM, and other
  peripherals. The 6800 has a data bus that is 8
  bits wide.

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What is a von Neumann Machine?

• von Neumann was a world-renowned mathematician.
  In 1952 he pointed out the primitive architecture
  of the ENIAC which had to be programmed by moving
  jumpers and cables and used 10 switches to
  represent the digits 0-9. von Neumanns machine
  used binary digits 0-1 and stored program and
  data in memory. The ALU had an accumulator.
  Todays computers are essentially von Neumann
  machines.

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What is a Virtual Machine?

• A Virtual Machine is a software implementation
  for which no direct hardware implementation
  exists. This is really a buzz word. All
  high-level languages and assembly languages are
  virtual machines ! The term Java Virtual
  Machine is being bandied about a lot these days.
  It is simply a Java Program. Ultimately, all
  virtual machines have to be implemented in
  hardware to get real results!

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Memory

• Big Endian 4 bytes arranged as0123 (32-bit
  word)
• Little Endian 4 bytes arranged 3210 (32-bit
  word)
• DRAM Organization
• nxn matrix structure is popular for large memory
  sizes
• RAS - Row Address Strobe
• CAS - Column Address Strobe
• RAS - CAS strategy reduces the number of pins but
  slows down access because two addressing cycles
  are required
• SRAM Fast for cache

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ROM

• ROM
• PROM
• EPROM - UV erasable
• EEPROM - Electrically erasable byte at a time
• FLASH - electrical block erasable - digital film
  - more like RAM!

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Hamming Code

• Detecting errors is easy (attach a parity bit)
• Correcting errors is complex and requires Hamming
  code with several parity bits
• Hamming distance between two code words is the
  number of single bit errors required to convert
  one code word to another. Example 1101 and 1110
  are a distance 2 apart
• n m r where r parity bits, m bits in the
  original data and n total number of bits
  transmitted

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2r gt mr1

• Example For 8-bit code one needs 4 parity bits
  for a total of 12 bits
• Parity bits are bits 1, 2, 4, 8 etc (P1, P2, P4,
  P8 )
• 3 12
• 5 14
• 6 24 P1 checks bits 3, 5, 7, 9, 11
• 7 124 P2 checks bits 3,6,7,10,11
• 9 18 P4 checks bits 5,6,7,12
• 10 28 P8 checks bits 9,10,11,12
• 11 128
• 12 48

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Problemo du Jour ...

• Example We need to send 11101001. What 12-bit
  Hamming word should we send?

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Solution de Problemo du Jour

• 101111001001

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IEEE 754 Floating Point Format (32-bit)

• 1 sign bit 8 exponent bits 23 significand bits
• sign bit is 0 for positive numbers and 1 for
  negative numbers
• exponent is in excess-127 format so an exponent
  of 4 will be written as 131 and an exponent of
  9 will be written as 118. Hence exponents can
  range from -127 to 128 (written as 0 through
  255)
• The normalized significand must be in the form
  1.xxxxx. Hence only the xxxxx part is actually
  written in the 23 bits and 1. is understood

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Convert 10.125 to IEEE-754 format

• 10.125 (decimal) 1010 .001000
• 1 .010001000 x 23
  (normalized)
• Our sign bit 0
• Our exponent 3 or 130 (excess 127) 10000010
• Our significand 0100010000 . . . ( 13 more
  zeros!)
• Putting it all together we get . . .
• 10.125 0100000100100010 . . . (16 more zeros)
• 41220000 (hex)