Computer Architecture and Assembly Language Quiz

The smallest unit of data in a computer, typically 8 bits.

A data type in assembly language that occupies four bytes in memory, representing a 32-bit integer.

Address of the next instruction to be executed by the CPU.

A type of jump instruction that transfers control to a target address within a limited range relative to the current instruction.

An addressing mode in assembly language where the operand's address is calculated based on the value stored in a register.

The process of converting a number from one base to another.

The instruction used to increment the value of a register by one.

The process of converting a number from decimal (base-10) to hexadecimal (base-16).

The mov instruction in assembly language does not directly increment the ECX register. It simply copies the value 26 into the ECX register.

In 2's complement representation, the most significant bit (MSB) indicates the sign of the number. If the MSB is 1, the number is negative.

The hexadecimal ASCII value of a character is its representation in the ASCII table using hexadecimal numbers.

A quadword, in computer architecture, is a data type that occupies 8 bytes (64 bits). It contains 4 words, where each word is 2 bytes (16 bits).

The 2's complement transformation of a number is calculated by inverting all its bits and then adding 1. This is a method used to represent negative numbers in computers.

The lowest possible signed value that can be stored in a byte is -128. This is because the most significant bit is used to represent the sign. If it's a 1, it signifies a negative number.

Little endian is a byte ordering scheme where the least significant byte is stored in the lowest memory address. This is contrasted with big endian, where the most significant byte is stored first.

Sign extension is the process of extending a number's binary representation to a larger size without changing its value. This is crucial when working with different data sizes, ensuring the sign (positive or negative) is preserved.

In x86 architecture, the Instruction Pointer (EIP) holds the address of the next instruction to be executed by the CPU. It acts as a program counter, keeping track of the program's flow. This ensures the instructions are executed in the correct order, allowing the program to run as intended.

The register indirect memory reference mode allows accessing data in memory using the address stored in a register. This mode provides flexibility as the register can be modified during the execution, enabling dynamic memory access.

The immediate mode in assembly instructions is a way to directly embed data within the instruction itself. This data is directly used by or loaded into a register/memory location, effectively making the data part of the instruction.

The Segment Registers (CS, DS, SS, ES, FS, GS) are special registers in x86 architecture that hold the base addresses of different memory segments. This segmentation helps organize memory and allows for different parts of code/data to be accessed independently. Each segment is like a separate area within the memory, and the segment register points to the beginning of that area.

The x86 architecture utilizes different addressing modes to access data in memory. These modes provide flexibility and efficiency in accessing data in different ways, depending on the specific needs of the program.

In the context of x86 architecture, the CPU (Central Processing Unit) is the brain of the computer, responsible for executing instructions and performing calculations. It contains various components, including the ALU, control unit, registers, and clock, working together to process data and make decisions.

The ALU (Arithmetic Logic Unit) is a crucial component within the CPU. It performs all the arithmetic and logic operations, enabling the computer to analyze and process data. It is responsible for adding, subtracting, comparing, and performing other essential calculations that form the basis of computer processing.

The clock is a fundamental component inside the CPU, setting the pace for all operations. It generates a regular, pulsating signal, synchronizing all activities within the CPU. Think of it as the heartbeat, keeping the CPU functioning in a rhythmic manner.

A directive used to allocate memory for data, typically at the beginning of a 64-bit assembly program.

A directive that specifies the memory model used for the program, which is "FLAT" in 64-bit assembly. It is used to indicate the memory layout for a program.

A directive used to specifically mark a memory space as a stack. However, it is not generally needed in 64-bit assembly programs since the stack is managed differently.

A directive used to define a region of memory used for storing instructions, which are usually executed during a program's runtime.

A variable declaration in assembly language that is used to allocate space for a 32-bit integer value.

A variable declaration in assembly language that is used to allocate space for a 64-bit integer value.

The instruction 'shl EAX, 2' shifts the bits in EAX register two positions to the left, filling the vacated positions with zeros. This effectively multiplies the original value in EAX by 4.

The 'not' instruction flips all the bits in BL, changing 0s to 1s and vice versa. The 'add BL, AL' then adds the original value in AL to the flipped value in BL. Because the values are flipped, the result is a binary representation of zero, which is 00 in hexadecimal.

The 'sar AX, 8' instruction shifts all the bits in AX register 8 positions to the right. The rightmost bits are discarded, so there are only 8 bits remaining in AX. Since AX holds 16 bits, those 8 bits remaining form the most significant 8 bits of AX.

The 'test' instruction performs a bitwise AND operation on EDX and the immediate value 150. The result of this operation is not stored. However, the EFLAGS register is updated based on the outcome of the operation. It is used for conditional jumps or branching.

The repeat prefix tells the processor to repeat the following operation until the ECX register reaches zero. The instruction 'cmpsb' compares the bytes pointed to by ESI (source) and EDI (destination). Both ESI and EDI are incremented after each comparison, so they are essential.

The 'movsd' instruction moves a double word from the source location pointed to by ESI to the destination location pointed to by EDI. It is the most efficient choice for minimizing the number of instruction executions in a loop.

The 'lodsb' instruction loads a byte from the memory location pointed to by ESI into AL. It increments ESI after the load, moving it to the next byte. The EDI register is not used in this instruction.

The CBW (Convert Byte to Word) instruction in assembly language takes the value in the AL register (8-bit) and extends it to the AX register (16-bit), preserving the sign. If the original AL value was positive, the higher byte in AX will be filled with zeros. If the original AL value was negative, the higher byte in AX will be filled with ones. This process ensures the correct representation of the signed value in a larger register.

The INC (Increment) instruction in assembly language adds 1 to the value of the specified operand. In the given code, INC BL increases the value in the BL register by 1. If BL initially contained 0FFh, after executing INC BL it will become 00h. This happens because of the rollover effect: when you increment a register that's already at its maximum value, it wraps back to 0.

The MOD R/M byte in an object code contains information about the addressing mode, including the register being used for addressing. The value 15 in the MOD R/M byte specifically signifies the use of the EBX register in the instruction. This indicates that the instruction is using the EBX register as part of the addressing mode. Understanding the MOD R/M byte is essential for dissecting object code and figuring out how instructions are accessing data.

The MOV instruction in assembly language is used for copying data from one location to another. If the object code contains 8B OD... This indicates that the second operand is a memory location. The opcode 8B signifies a MOV instruction, and the MOD R/M byte OD indicates that the destination operand (second operand) is a memory location. This tells us that the instruction is moving data from a memory location into the register specified as the first operand.

The NEG (Negate) instruction in assembly language changes the sign of its operand by taking the 2's complement. This means that if the operand is positive, it becomes negative, and vice versa. In the given line of object code F7 DB, the opcode F7 indicates a NEG instruction. The second byte DB indicates that the operand is in the BL register. So, this instruction would negate the value stored in the BL register.

The SUB (Subtract) instruction in assembly language subtracts the second operand from the first operand. In the given context, SUB AL, BL subtracts the value in the BL register from the value in the AL register. The result is then stored in the AL register. The Sign Flag (SF) and Zero Flag (ZF) are often used to determine the outcome of arithmetic operations. The Sign Flag indicates the sign of the result. If the result is negative, the Sign Flag is set to 1. If the result is positive, the Sign Flag is set to 0. The Zero Flag indicates whether the result is zero. If the result is zero, the Zero Flag is set to 1. Given that AL = -1 and BL = -2, when you subtract BL from AL, the result will be 1. Since the result is positive, the Sign Flag will be 0, and since the result is not zero, the Zero Flag will be 0.