Computer Organization Chapter 2

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Questions and Answers

What is the comparison instruction used for unsigned numbers in RISC-V?

blt

bgeu (correct)

bltu (correct)

bge

What is the purpose of the lui instruction in RISC-V?

To load a 32-bit constant into a register (correct)

To perform a signed comparison

To assign a symbol to a value in the assembler

To check for index out of bound

How are negative numbers treated when comparing unsigned numbers in RISC-V?

As undefined

As smaller than any positive number

As equal to zero

As larger than any positive number (correct)

What is the purpose of the EQU command in the assembler?

To assign a symbol to a value Signup and view all the answers

What is the result of comparing x22 and x23 in signed comparison?

x22 < x23 Signup and view all the answers

What is the result of comparing x22 and x23 in unsigned comparison?

x22 > x23 Signup and view all the answers

What is the instruction used to check for index out of bound in RISC-V?

bgeu X20, X10, IndexOutofBound Signup and view all the answers

What is the effect of the lui instruction on the bits [11:0] of the register?

Sets them to 0 Signup and view all the answers

What is a major advantage of using registers instead of memory?

Registers are faster to access than memory Signup and view all the answers

What is the purpose of immediate operands in instructions?

To make the common case fast by avoiding a load instruction Signup and view all the answers

What is the range of unsigned binary integers in a 64-bit representation?

0 to +18,446,774,073,709,551,615 Signup and view all the answers

What is the significance of the sign bit in 2s-complement signed integers?

It indicates whether the number is negative or non-negative Signup and view all the answers

What is the process of signed negation in 2s-complement signed integers?

Complement and add 1 Signup and view all the answers

What is the purpose of sign extension in 2s-complement signed integers?

To preserve the numeric value Signup and view all the answers

What is the range of 2s-complement signed integers in a 64-bit representation?

–9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 Signup and view all the answers

What is the representation of the most-positive number in 2s-complement signed integers?

0111 1111 … 1111 Signup and view all the answers

What is the main purpose of extending unsigned values with 0s?

To make the representation of signed and unsigned values consistent Signup and view all the answers

What is the advantage of using RISC-V instruction set?

It is simpler and has fewer instructions Signup and view all the answers

What is the opcode in a RISC-V R-format instruction?

A 7-bit operation code Signup and view all the answers

What is the purpose of the offset in memory segmentation?

To specify the start address of a segment Signup and view all the answers

What is the purpose of the funct3 field in a RISC-V R-format instruction?

To provide additional opcode information Signup and view all the answers

What is the hexadecimal representation of the binary number 1110 1100?

EC Signup and view all the answers

What is the main difference between lb and lbu instructions in RISC-V?

lb is used for signed values, while lbu is used for unsigned values Signup and view all the answers

What is the purpose of the immediate field in a RISC-V I-format instruction?

To provide a constant operand or offset Signup and view all the answers

What is the main advantage of using a stored-program computer architecture?

It enables programs to operate on other programs Signup and view all the answers

What is the purpose of the funct7 field in a RISC-V R-format instruction?

To provide additional opcode information Signup and view all the answers

What is the effect of shifting a binary number left logically by 1 bit?

It multiplies the number by 2 Signup and view all the answers

What is the purpose of the rs1 field in a RISC-V I-format instruction?

To specify the source register Signup and view all the answers

Study Notes

Memory and Registers

Registers are faster to access than memory.
Operating on memory data requires loads and stores, which are more instructions to execute.
Compilers use registers for variables as much as possible and spill to memory for less frequently used variables.
Register optimization is important.

Memory Hierarchy

CPU Registers are the fastest and most accessible to store even important required permanent data.

Immediate Operands

Constant data specified in an instruction, e.g., addi x22, x22, 4.
Small constants are common, and immediate operands avoid a load instruction.

Unsigned Binary Integers

Given an n-bit number, x = x n-1 2n-1 + x n-2 2n-2 + … + x1 21 + x0 20.
Range: 0 to +2n – 1.
Example: 0000 0000 … 0000 1011 two = 0 + … + 8 + 0 + 2 + 1 = 11.

2's-Complement Signed Integers

Given an n-bit number, x = -x n-1 2n-1 + x n-2 2n-2 + … + x1 21 + x0 20.
Range: –2n – 1 to +2n – 1 – 1.
Example: 1111 1111 … 1111 1100 two = –1×231 + 1×230 + … + 1×22 + 0×21 +0×20 = –2,147,483,648 + 2,147,483,644 = –410.

Signed Negation

Complement and add 1.
Example: negate +2, +2 = 0000 0000 … 0010 two, –2 = 1111 1111 … 1101 two + 1.

Sign Extension

Representing a number using more bits, preserving the numeric value.
Replicate the sign bit to the left.
Example: x22 = 1111 1111 1111 1111 1111 1111 1111 1111, x23 = 0000 0000 0000 0000 0000 0000 0000 0001.

Bound Check

We can check index out of bound by treating signed numbers as unsigned.
Example: bgeu X20, X10, IndexOutOfBounds.

Load Upper Immediate

Most constants are small, and a 12-bit immediate is sufficient.
For the occasional 32-bit constant, lui rd, constant.
Example: lui x19, 976 and addi x19, x19, 1280.

Representing Instructions

Instructions are encoded in binary, called machine code.
RISC-V instructions are encoded as 32-bit instruction words with a small number of formats encoding operation code, register numbers, etc.

Hexadecimal

A compact representation of bit strings, 4 bits per hex digit.

RISC-V Instructions

R-format instructions: funct7 rs2 rs1 funct3 rd opcode.
I-format instructions: immediate rs1 funct3 rd opcode.
S-format instructions: imm[11:5] rs2 rs1 funct3 imm[4:0] opcode.

Stored Program Computers

Instructions are represented in binary, just like data.
Instructions and data are stored in memory.
Programs can operate on programs, e.g., compilers, linkers.
Binary compatibility allows compiled programs to work on different computers.

Logical Operations

Instructions for bitwise manipulation: and, andi, or, ori, xor, xori.
Shift operations: slli, srli.
Shift left logical: slli by i bits multiplies by 2i.
Shift right logical: srli by i bits divides by 2i (unsigned only).

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Description

Understand the basics of computer organization, including registers, memory, and instruction sets. Learn about the language of the computer and how it processes information.