What does SIB byte mean?
The SIB byte then includes the following fields: The ss field, which occupies the two most significant bits of the byte, specifies the scale factor. The index field, which occupies the next three bits following the ss field and specifies the register number of the index register.
What is a REX prefix?
The rex family of prefixes is used by x86-64 to encode extensions to i386 instruction set. The rex prefix has four bits — an operand size overwrite (64) used to change operand size from 32-bit to 64-bit and X, Y and Z extensions bits used to extend the register set.
What is ModR M byte?
The ModR/M byte is central to the changes introduced with AMD’s 64-bit extension to the original instruction set. In long mode, any opcode whose highest four bits are 0100 (decimal 4) are considered to be a new prefix, the REX prefix.
What are the values of the SIB ModR m and displacement bytes for the x86 instruction?
Opcode with prefixes (1-4 bytes, required) ModR/M (1 byte, if required) SIB (1 byte, if required) Displacement (1, 2, 4 or 8 bytes, if required)
What is the difference between 86 bit and 64-bit?
Conclusion: The biggest difference between x86 and x64 is that they can access the different amounts of RAM. The x86 (32-bit processors) has a limited amount of maximum physical memory at 4 GB, while x64 (64-bit processors) can handle 8, 16, and some even 32GB physical memory.
What is MOV in assembly language?
mov — Move (Opcodes: 88, 89, 8A, 8B, 8C, 8E.) The mov instruction copies the data item referred to by its second operand (i.e. register contents, memory contents, or a constant value) into the location referred to by its first operand (i.e. a register or memory).
What do you mean by x86?
X86 is the term used to denote the microprocessor family based on the Intel 8086 and 8088 microprocessors. These microprocessors ensure backward compatibility for instruction set architectures. Initially x86 started with an 8-bit instruction set, but then grew to 16- and 32-bit instruction sets.
What is Mod field in microprocessor?
The MOD field shows the mode of addressing. The MOD, R/M, REG and the ‘W’ fields are decided in Table 2.2. 4 Register to/from Memory with Displacement: This type of instruction format contains 1 or 2 additional bytes for displacement along with 2 byte format of the register to/from memory without displacement.
What do you mean by an instruction code?
An instruction code is a group of bits that instruct the computer to perform a specific operation. • The operation code of an instruction is a group of bits that define operations such as addition, subtraction, shift, complement, etc.
How is opcode size calculated?
As the processor has 40 instructions, number of bits for opcode = 6 (2^6 = 64) As the processor has 24 register, number of bits for one register = 5 (2^5 = 32) Total bits occupied by 2 registers and opcode = 6 + 5 + 5 =16. As instruction size given is 32 bits, remaining bit left for operand = 32-16 = 16 bits.
Why are 32-bit called x86?
x86 is the name of the architecture that it’s built to run on (the name comes from a series of old Intel processors, the names of which all ended in 86, The first of which was the 8086). Although x86 was originally a 16-bit architecture, the version in use today is the 32-bit extension.
Why is x86 still used?
The x86 processors allow you to perform several activities at the same time from a single instruction. Also, they can perform numerous simultaneous tasks without any of them being affected.
What does mov ah 4ch mean?
mov ah,4ch is the first line of assembler code. The value 4C in hexadecimal is stored in the register AH. int 21h is the second line of assembler code. The software interrupt 21h is called. This interrupt, when given the value of 4ch in AH (as is the case here), causes the program to exit immediately.
Is mov an opcode?
“mov” is an instruction, encoded with the operation code or “opcode” 0xb8. Since mov takes an argument, the next 4 bytes are the constant to move into eax. The opcode 0xb9 moves a constant into ecx.
What is x86 and x64 means?
x86 refers to a 32-bit CPU and operating system while x64 refers to a 64-bit CPU and operating system.
Why is it called x86 and not x32?
What is opcode size?
As the processor has 45 instructions, number of bits for opcode = 6 (2^6 = 64) Total bits occupied by 2 registers and opcode = 6 + 6 + 6 =18. As instruction size given is 32 bits, remaining bit left for immediate operand = 32-18 = 14 bits. Maximum unsigned value using 14 bits = 2^14 – 1 = 16383 which is the answer.
What are the 8 different types of instruction in 8086?
Microprocessor – 8086 Instruction Sets
- Data Transfer Instructions.
- Arithmetic Instructions.
- Bit Manipulation Instructions.
- String Instructions.
- Program Execution Transfer Instructions (Branch & Loop Instructions)
- Processor Control Instructions.
- Iteration Control Instructions.
- Interrupt Instructions.
How many types of instruction codes are there?
A basic computer has three instruction code formats which are: Memory – reference instruction. Register – reference instruction. Input-Output instruction.
What are the types of instruction?
Types of Instruction
- Direct instruction. The Direct instruction strategy is highly teacher-directed and is among the most commonly used.
- Indirect instruction.
- Independent study.
- Interactive instruction.
- Experiential Learning.
How many bits are in an opcode?
The J instruction format
| Opcode | Address |
|---|---|
| 6 bits | 26 bits |
What is opcode and operand?
Opcodes and operands
The opcode is the instruction that is executed by the CPU and the operand is the data or memory location used to execute that instruction.
Are there 128 bit processors?
CPUs that process 128 bits as a single unit, compared to 8, 16, 32 or 64 bits. As of 2022, there are no 128-bit computers on the market. A 128-bit processor may never occur because there is no practical reason for doubling the basic register size.
Why is 64-bit called x64?
AMD originally used the AMD64 moniker for this new platform, but then Intel started making AMD64 compatible chips (as Intel 64), and it was renamed to x64 because it wasn’t an AMD exclusivity anymore.
Will we ever need 128 bit?
A 128-bit processor may never occur because there is no practical reason for doubling the basic register size. One of the reasons for migrating from 32-bit to 64-bit computers was memory (RAM) addressing; however, for all practical purposes, there was only a need for a few more bits beyond 32 (see binary values).