CSCI 211 Intro
• Computer Organization
– Consists of gates for logic
• And
• Or
• Not
– Processor
– Memory
– I/O interface
Instructions
• Instructions are in memory
– Fetch instruction, then execute it
• Fetch execute cycle
– More detailed
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Fetch instruction
Fetch operands
Execute instruction
Save result
Determine next instruction
Processor Components
• Datapath
– Hardware that electrons flow through to
accomplish an instruction
• Control
– Tells hardware what to do and when to do it.
• Registers
– Small amount of memory (32 4-byte for MIPS)
that can be operated upon.
What’s inside
• Everything in the computer is represented
with 0’s and 1’s (on-off)
– Integers
– Characters
– Boolean
– Float
– Instructions (machine language)
Languages
• Machine Language
– Just 0’s and 1’s
– Very hard to program
• Assembly
– Symbolic for machine language
– Easy to create a program to translate from
assembly language to machine language
(almost 1 to 1)
– Keeps track of variables’ addresses
Why Learn Assembler
• Understand what the machine does
– Helps you to be a better guesser
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Needed to write a compiler (431)
Needed to build CPUs
Faster to execute
To determine timing
Gives you the power to access anything
Maintaining older systems
Why not USE assembly
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Tedious
Error prone
Slow to write
Machine dependent
Good compilers produce fast code already
MIPS CPU
• Used in many systems
– SGI workstations
– Sony PS2
– Dish Network set top box
– Tivo DVR
– Pioneer Plasma TV
– HP Color laser printer
– Many more
MIPS Layout
• Control
• Register file (32 registers with 32 bits
each)
• ALU
• Program Counter (PC)
• Memory
– 32 bit address (232 bytes addressable = 4Gb)
• Instruction register (IR)
Control Unit
• Sends the proper control signals to each
component to accomplish instruction
• Input to the control unit
– Instruction
– Cycle number – which step of the instruction
Register File
• A group of registers
• Input
– Which register (5 bits)
– Read or Write
– 32 bit value (for write)
– Outputs a 32 bit value for read
Register Conventions
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$0 = 0
$1 – used by the assembler
$2, $3 – function return values
$4-$7 – Arguments to a function
Etc.
Other components
• ALU
– Performs arithmetic and logic (and, or, shift)
• PC
– Program counter – address of next instruction
• Memory
– 32 bit address
– Addresses a byte (8 bits)
– Some instructions use word (4 bytes),
halfword (2 bytes), or byte operands
– All instructions are 4 bytes (on MIPS)
• PC=PC+4
Instruction Register
• IR
– Holds the 32 bit instruction just fetched
– Needed for control unit to determine what
control signals to send
Instruction Format
• Opcode
– First 6 bits
• 3 Formats
– R type
• Opcode all 0’s
• Three 5-bit fields for registers (2 for operand, 1 for
result)
• 5-bit shift amount (for shift instructions)
• 6-bit function code
Other formats
• I Type
– Two 5-bit register numbers
– 16-bit value as the third operand
• J type
– Jump instructions
– 26 bit address field (64M)