quartz/content/notes/04-computer-architecture.md

title	aliases	tags
04-computer-architecture		cosc204

• tristate buffer slide
• circuit simulator
• 

Bus

• data bus

• address bus

• control bus

• conmmunicate between parts of the computer

• only one transmitter at a time

• only addressed device can respond

• 2 levels

  • internal
  • external

Memory

• memory size is dependent on bus size

  • 2n bytes for n-lines on the address bus
    • 2^8=256B, 2^16=64KB, 2^32=4GB, 2^64=16EB

• flip flops are grouped into bytes (or larger)

  • each byte has an address
  • to write
    • present the address and the data
    • tell chip to write
  • to read
    • present the address
    • tell the chip to read
    • look at the data

Static RAM (SRAM)

• memory made from flip flops is called static RAM
  • used mostly in CPU cache
  • or anywhere where only a small amount is needed
  • expensive

Dynamic RAM (DRAM)

• made from capacitors
• used where large amount of RAM is needed
• slower than SRAM
• inexpensive

Non-Volatile Memory

• often called ROM (read only memory)
  • can also be called PROM, EPROM, EEPROM, FLASH
• flash
  • uses floating-gate flash cells, not quite a transistor

ALU

• performs arithmetic
  • add, subtract, etc.
• logical operations
  • and, or, shift, etc
• subunits
  • lofical operations
  • addition
  • multiplication and dividion
  • shifting
  • comparison
  • logical tests (if, >0, <0, =0, <=0, etc)

Control unit

• coordinates the operation of the computer
• generates control signals
  • connect registers to the bus
  • control the function of the ALU
  • provides timing signals to the system

allso associated with the decoding and executuion of instructions in a pipelined system

Registers

• memory cells with names
• hold data, instructions, or CPU status
• various sizes, (8, 16, 32, or 64, or larger (512))
• hold data typically the same width as memory words
• registers for accessing memory typically the same with as the address bus

Special purpose registers

• program counter
  • stores address of current instruction
• accumulator
  • source of one of the operands
  • destination of the result
• status flags
  • individaul bits store information about results of operations
    • result of last instruction was negative, zero, or postive
    • carry from most recent arithmetic operation
    • overflow occurred during the last instruction

CPU

Computer

Instructions

• bit patterns
• can be split into a number of fields
  • operation to be executed
  • the address in memory
  • which registers (or memory cells) to use as operands
  • where to place the result (registers or memory)

Stored program computer

Von Neumann Architecture

• three key concepts
  • data and instructions are stored in a single read-write memory
  • contents of memory are addressable by location, without regard to the type of data contained
  • execution occurs in a sequential fashion, unless explicitly altered, from one instuction to the next