Csc 215 Past Questions and Answers

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CSC 215

Solutions

1

The addressing mode of a computer memory refers to the way in which the CPU accesses data stored in memory. There are several addressing modes, including direct addressing, indirect addressing, indexed addressing, relative addressing, and immediate addressing. Each of these modes involves different methods for specifying the location of the data to be accessed in memory. The choice of addressing mode can have an impact on the efficiency and speed of memory access in a computer system.

2.

2a. Four advantages of a low-level programming language over a high-level programming language are:

1. Control: Low-level programming languages offer more control over the hardware of a computer system, allowing programmers to write code that can execute more efficiently and with greater precision.
2. Efficiency: Low-level programming languages are often faster and more efficient than high-level programming languages because they require fewer system resources to run.
3. Flexibility: Low-level programming languages are more flexible than high-level programming languages because they allow programmers to write code that is tailored to the specific needs of a particular application.
4. Portability: Low-level programming languages are often more portable than high-level programming languages because they are closer to the machine language of a computer system, which means that they can be used on a wider range of hardware platforms.

2b. The four types of data types in Assembly Language are:

1. Byte: A byte is a data type that represents a single character or number. It is typically 8 bits in size.
2. Word: A word is a data type that represents a group of bytes. The size of a word can vary depending on the computer architecture, but it is typically 16 or 32 bits in size.
3. Double word: A double word is a data type that represents two words. The size of a double word can vary depending on the computer architecture, but it is typically 32 or 64 bits in size.
4. Quad word: A quad word is a data type that represents four words. The size of a quad word can vary depending on the computer architecture, but it is typically 64 or 128 bits in size.

3

3a. The three execution cycles in the order of precedence are:

1. Fetch cycle: During the fetch cycle, the CPU retrieves the instruction from memory and prepares it for execution.
2. Decode cycle: During the decode cycle, the CPU interprets the instruction and determines what operation it needs to perform.
3. Execute cycle: During the execute cycle, the CPU performs the operation specified by the instruction and stores the results in memory or in a register.

3b. Indirect addressing mode is a method of addressing memory in which the address of the operand is not specified directly, but is instead stored in a register or memory location. The CPU retrieves the address from the specified location and uses it to access the operand in memory.

For example, suppose we have a register called R1 that contains the memory address of a value we want to retrieve. We can use indirect addressing mode to access the value by specifying the register as the operand in the instruction. The CPU will retrieve the address from R1 and use it to access the value in memory.

Indirect addressing mode is useful for situations where the address of the operand is not known in advance, or where it needs to be calculated dynamically during program execution. It can also be used to simplify the addressing of complex data structures, such as arrays or linked lists.

4

Here is an example program in Assembly Language that will initiate two registers, add their contents, and store the result in a third register, along with the address of the next operation:

        ORG 0x0000       ; Set the origin to 0x0000

START:  MOV R1, #5        ; Initialize R1 with the value 5
        MOV R2, #10       ; Initialize R2 with the value 10
        ADD R3, R1, R2    ; Add the contents of R1 and R2, store the result in R3
        MOV R4, PC        ; Store the address of the next instruction in R4
        B END             ; Branch to the end of the program

END:    ...

        END              ; End of the program

In this program, the MOV instruction is used to initialize registers R1 and R2 with the values 5 and 10, respectively. The ADD instruction is used to add the contents of R1 and R2, and store the result in R3. Finally, the MOV instruction is used again to store the address of the next instruction in R4, and the program branches to the end of the program.

4b. In Assembly Language, an operand is a value or memory location that is operated on by an instruction. For example, in the instruction ADD R1, R2, #10, R1 and R2 are the operands, and #10 is an immediate value that is added to the contents of R2.

An op-code, on the other hand, is a code that specifies the operation to be performed by the instruction. For example, in the ADD instruction, the op-code is 0001, which specifies that the contents of the two operands should be added together. The op-code is typically the first few bits of the instruction, and it determines what operation will be performed and how the operands will be interpreted.

5

5a. The syntax of an Assembly Language program consists of a series of instructions, each of which is composed of one or more fields. The basic structure of an instruction is as follows:

[label] opcode operand1, operand2, ...

The label field is optional and is used to give the instruction a symbolic name. The opcode field specifies the operation to be performed, and the operand fields specify the data or memory locations to be operated on. The operands can take several forms, including register names, immediate values, memory addresses, and labels.

The syntax of an Assembly Language program is typically determined by the assembler being used, which may have its own specific syntax rules and conventions. In general, Assembly Language programs are written in a text editor and saved with a .asm file extension. The program is then assembled by a separate program called an assembler, which translates the program into machine code.

5b. Data registers, pointer registers, and index registers are all types of general-purpose registers that are used to hold data and perform arithmetic and logical operations. Here are the functions of two of these registers:

(i) Data registers: These registers are used to hold data values that are being operated on by the program. They are typically used for arithmetic and logical operations, such as addition, subtraction, multiplication, and division. Data registers can also be used to store intermediate results and to hold function arguments and return values. The number of data registers available in a particular processor architecture varies, but most architectures have at least a few general-purpose data registers.

(ii) Pointer registers: These registers are used to hold memory addresses, which are used to access data stored in memory. Pointer registers are typically used for operations such as loading and storing data to and from memory, and for accessing data structures such as arrays, strings, and linked lists. Pointer registers are often used in conjunction with index registers to perform complex memory operations. The number of pointer registers available in a particular processor architecture varies, but most architectures have at least one or two general-purpose pointer registers.

6

6a. The 8088 and 8086 processors have two operating modes: real mode and protected mode. In real mode, the processor behaves like an 8086 processor, with a 20-bit address bus and support for up to 1 MB of memory. In protected mode, the processor can access up to 4 GB of memory and has support for features such as virtual memory, multitasking, and memory protection. Protected mode also includes support for 32-bit and 64-bit operating systems.

6b. Here is an explanation of each line of the assembly language program and the type of addressing mode used:

MOV BX, TAX_RATE  ; Direct addressing mode

This line moves the value stored in the memory location labeled TAX_RATE into the BX register. The TAX_RATE label is assumed to be a memory address, and the value stored at that address is loaded into the BX register. This is an example of direct addressing mode, where the operand specifies the memory location directly.

MOV EAX, 68  ; Immediate addressing mode

This line moves the immediate value 68 into the EAX register. Immediate addressing mode is used when the operand is a constant value that is included in the instruction itself.

MOV BX, EAX  ; Register addressing mode

This line moves the value stored in the EAX register into the BX register. Register addressing mode is used when the operand is a register.

ADD BX, EAX  ; Register addressing mode

This line adds the value stored in the EAX register to the value stored in the BX register, and stores the result in the BX register. This is an example of register addressing mode, where the operand is a register.