Organization of Computers Midterm

What two things can a computer do?

Store state and manipulate state

How many bytes (byte-addressable) can a k-bit address specify?

2^k

What is a register file?

A synchronous RAM

What is the write data port in the register file?

The data that will be written

What is the write address port in the register file?

The location the data will be written to

We need to build a RAM that can store 128, 64-bit words and
has one write port and three read ports
How many address bits does my RAM need for its write port?

7

We need to build a RAM that can store 128, 64-bit words and
has one write port and three read ports
How many data bits does my RAM need for each read port?

64

What are the 3 parts of a register file?

1. The Storage: An array of registers

2. The Read Ports: Output the data of the register indicated by read addresses

3. The Write Port: Selectively write data to the register indicated by write address

5

How many registers does a 4 × 16-bit register file have?

4 registers (2 bits)

How many data bits does a 4 × 16 register file have?

16 bits

What is the key feature that distinguishes a computer processor from other digital systems?

Programmability

What is a processor?

A hardware system controlled by software

What is an Instruction Set Architecture?

Describes the interface between the software and the hardware. ISA specifies what operations are available. ISA specifies the effects of each operation.

What do instructions consist of?

Operation code: names the operation to perform

Operands:Names the data to operate on

What are register instructions?

R-Type. Require all values to be stored in registers

What is the size of the MIPS register file?

32 × 32 bits

add $14, $18, $3

Which registers are being added together, and in what order?

$18 + $3

add $14, $18, $3

Which register stores the result?

$14

add $14, $18, $3

What is another name for $18?

rs

add $14, $18, $3

What is another name for $3?

rt

add $14, $18, $3

What is another name for $14?

rd

What are I-Type Instructions?

These instructions allow you to specify an immediate value for the second source instead of a register

addi $15, $1, 4

Which values are being added together, and in what order?

$1 + 4

addi $15, $1, 4

Which register stores the result?

$15

addi $15, $1, 4

What is another name for $15?

rt

addi $15, $1, 4

What is another name for $1?

rs

How could a constant be written to a register?

addi $15, $0, 4

How does sign extension work?

The most significant bit of the input is used to extend the number of bits to represent that value

Where are values store in an I-Type Instruction?

rt

Where are values stored in an R-Type instruction?

rd

What are valid addresses for MIPS Instructions?

0,4,8, 12, etc

What is the Program Counter (PC)?

The PC contains the address of the next instruction to execute

Why can the 2 LSb's of the PC be neglected?

Since the only valid instruction addresses are divisible by 4, the first 2 bits will always be 00

Explain the format of the jump instruction

j target_label. Uses a label to tell where in the code to jump to

How many bits are allotted for the address in a J-Type instruction?

26 bits

Where do the other 6 bits come from for the address in a J-Type instruction?

The bottom two bits are always 00 and the 4 MSb’s are the MSb’s of the PC

What is the format for beq? And what is the comparison?

beg rs, rt, target_label

R[rs] == R[rt]

What type of instruction are branch instructions?

I-Type

How is the target label_stored in branch instructions

The constant field is not an address, but an offset from the current PC to the target address.

What is the value stored in L?

3, Since the PC points to the next instruction, you dont count' from the instruction being run, but from where the PC is pointing

How many bits is the PC incremented by to reach label L?

3×4 = 12 bits. The PC moves forward 12 bytes in memory

What is the range of the j instruction?

256 MB

Why would you want to use the jr instruction?

If you want to jump outside the bounds of the j instruction

What is another name for the register that is used in jr?

rs

How does jr allow you to leave the bounds established by j?

jr is provided with a register. This register contains an address to jump to. Allows you to fill the entire register with the desired address

What type of instruction is jr?

R-Type

How large is the immediate in I-Type instructions?

16 bits

What does the lui instruction do?

loads the highest 16 bits of a register with a constant, and clears the lowest 16 bits to 0’s

What is the format of lui?

lui $rt, Imm

What value is stored in $12?

lui $12, 0×3D

ori $12, $12, 0x900

0x003D 0900

What type of instruction is lui?

I-Type

What is the format of slt?

slt rd, rs, rt

What is the format for slti?

slti rd, rs, imm

How much storage does the MIPS architecture have by default?

2^(32) * 8 = 4GB

In data memory, what is the operation if word_we = 0 and byte_we = 0?

Read from the address in ADDR

In data memory, what is the operation if word_we = 0 and byte_we = 1?

Write a byte in ADDR

In data memory, what is the operation if word_we = 1 and byte_we = 0?

Write a word in ADDR

How large is a word in MIPS?

32 bits

What does lw do?

Transfers one word of data from the data memory to a register

What does sw do?

Transfers one word of data from a register into main memory

lw $12, 4($3)

What is another name for $12?

rt

sw $12, 4($3)

What is another name for $12?

rt

lw $12, 4($3)

What is another name for $3?

rs

sw $12, 4($3)

What is another name for $3?

rs

What is the unit of the offset in lw/sw/lbu/sb?

bytes

What does lbu do?

Transfers one byte of data from the data memory to a register and zero extends it

What does sb do?

Transfers one byte of data from a register into main memory

Which byte is transferred in sb?

The LSB