Any attempt to use the registers for any other purpose may result in considerable grief, especially if you intend to move up to a better CPU like the 80386. rcx - register c extended. 14. The segment registers have a very special purpose - pointing at accessible blocks of memory. rbp - register base pointer (start of stack) rsp - register stack pointer (current location in stack, growing downwards) c) Accumulators. The 80386 architecture takes advantage of this by providing mechanisms to support direct access to the instructions and data of the current modules environment with access to additional segments on demand. The special-purpose registers include EIP, ESP, EFLAGS; and the segment registers CS, DS, ES, SS, FS, and GS. 4.1.3 8086 Special Purpose Registers . (starting with the 80386) also include various special/miscellaneous registers such as control registers (CR0 through 4, CR8 for 64-bit only . An accumulator is a register for short-term, intermediate storage of arithmetic and logic data in a computer's CPU (Central . regs. The general registers, Figure 2-2, support data operands of 1, 8, 16, 32 and 64 bits, and bit fields of. REGISTER SET-80386 It included all eight general purpose registers plus the four segment registers. Register A is quite often called as an Accumulator. Although there are certainly still special-purpose registers for some instructions (typically for historical or compatibility reasons), the majority of the instructions are structured so that there are preferred registers that you can override if desired. General Purpose Register • The 80386 contains 32-bit general purpose register called EAX, EBX, ECX, EDx, ESP,EBP, ESI, and EDI. You can access any register depending upon the size of your data. The extended register set of the 80386 provides programmers with the best of both worlds. Real operating mode • The 80386 has eight 32 - bit general purpose registers which may be used as either 8 bit or 16 bit registers. The general-purpose registers (or GPRs) are the primary registers in the x86-64 register model. This register is addressed as either BP or EBP. - David Cary. c) Ease of programming. When running in protected mode, the 80386 continually checks that the application is privileged enough to Execute certain instructions. Most of the special-purpose operations that the 80386 inherited from the 8086 are largely obsolete. • A 32 - bit register known as an extended register, is represented by the register name with prefix E. • Example : A 32 bit register corresponding to AX is EAX, similarly BX is EBX etc. Which of the following is a special-purpose register of microprocessor? • The lower 16-bits of each of the general purpose register can be accessed individually. The 80386 has eight general-purpose 32 bit registers EAX, EBX, ECX, EDX, ESI, EDI, EBP and ESP. Reference data other than its own. x86 processors that have a protected mode, i.e. Lower half of each of the ZMM registers maps onto the corresponding YMM register. According to sources, the 80386 was the first processor in this line with FS and GS registers, and so it would be incorrect to include them in a list of the 8086 registers. 2.3.1 General Registers The general registers of the 80386 are the 32-bit registers EAX, EBX, ECX, EDX, EBP, ESP, ESI, and EDI. General purpose registers are accessed and are designed to keep 8, 16, or 32-bit data whereas segment registers include a segment address in real mode operation and they a selector in protected mode operation. It is the 64 bit version of the 8088/8086 CX, or 32 bit 80386 ECX . The above forms of MOV store or load the following special registers in or from a general purpose register: Control registers CR0, CR2, and CR3. d) Registers . • The 80386 supports four types of descriptor table, viz. • A 16 bit instruction pointer IP is available along with 32 bit counterpart EIP. Also, it consists of 8 general purpose as well as 8 special purpose registers. Special purpose registers (16-bit): Special purpose registers are called Offset registers also. To store more than 8 bits, we have to use two registers in pairs. 80386 has a data bus of 32-bit. 32-bit Processors-80386, 80387 and 80486. Many times there were related special purpose registers that contained the source data for an accumulator. d) All of the above. 80386. c) 80486. d) Pentium. . . It is of 16 bits and is divided into two 8-bit registers AH and AL to also perform 8-bit instructions. These registers are used interchangeably to contain the operands of logical and arithmetic operations. VM (Virtual Mode): When 0, the CPU can operate in Protected mode, 286 Emulation mode or Real mode. a good idea. But be careful about what you read, since it has things like: > In fact, I occasionally name my variables . . Description The above forms of MOV store or load the following special registers in or from a general purpose register: Control registers CR0, CR2, and CR3 Debug Registers DR0, DR1, DR2, DR3, DR6, and DR7 Test Registers TR6 and TR7 32-bit operands are always used with these instructions, regardless of the operand-size attribute. The photo above shows the silicon die of the 8086 processor under a microscope. General Purpose Registers: The eight general pur-pose registers of 32 bits hold data or address quanti-ties. eax, ecx etc are sgeneral purpose register because you can use them for everything without (almost) no limits. Miscellaneous/special purpose. The 8086 architecture consists of 4 general-purpose registers of 16 bits. . For example, cs, ds, gs and the other segment registers fall into the special purpose registers, because they exist to hold segments' number. System Address Registers • System Address Registers are special registers which are defined to reference the tables or segments supported by the 80286 . A special purpose register is one that has a specific control or data handling task to carry out. Miscellaneous/special purpose. The 80386 processor generalized the memory addressing modes. System Address Registers: Four special registers . The general purpose registers were 16 bit wide in earlier machines, but in 386 these registers can be extended to 32 bit. Their new names are EAX,EBX,ECX and so on. Figure - General purpose registers AX - This is the accumulator. • The CS and SS are the code and the stack segment registers respectively, while DS, ES,FS, GS are 4 data segment registers. It supports physical memory addressability of 4 GB and virtual memory addressability of 64 TB. Furthermore, the 80386 introduced new scaled indexed addressing modes that simplify accessing elements of arrays. Transfer control to code other than its own. When set, the CPU is converted to a high speed . Special of 80386 registers 1. 9) The registers available to the user can be further classified into:-a) General purpose register b) Special-purpose register The metal layer on top of the chip is visible, with the silicon hidden underneath. To ensure compatibility with the earlier 8086 processor, the lower half of each register can be accessed as a 16-bit register (AX, BX, CX, DX, SI, DI, BP and . The figure below shows the architectural representation of 80386 microprocessor: . The section contains questions and answers on features, architecture, register organisation, addressing modes, instruction set, paging and segmentation on 32 bit . The accumulator register (AX), Base Register (BX), Counter Register (CX), and a data register (DX) are of 16 bits each. • It is used to hold instruction operand. In the real mode, 80386 works as a fast 8086 with 32-bit registers and data types. These . 32-bit operands are always used with these instructions, regardless of the operand-size attribute. There are a number of . Debug Registers DR0, DR1, DR2, DR3, DR6, and DR7. The general purpose registers are used to store temporary data in the time of different operations in microprocessor. Whereas the 8086 only allowed you to use bx or bp as base registers and si or di as index registers, the 80386 lets you use almost any general purpose 32 bit register as a base or index register. 4.6.4 80386 Memory Addressing Modes . Z (Zero): 1 if the result of an arithmetic or logic instruction is 0. . . The problem with the x86 serie of processors is that there are few registers to use. (starting with the 80386) also include various special/miscellaneous registers such as control registers (CR0 through 4, CR8 for 64-bit only . Memory Management Unit. The eight general-purpose registers all have 32 bit equivalents. A good assembly language programmer should use general purpose registers rather than memory in maximum possible ways for data processing. General purpose registers are used to store temporary data within the microprocessor. Pentium and up: . 80386 and up: RF (Resume): Used with debugging to selectively mask some exceptions. 5. a) Program counter b) Instruction register c) Accumulator . 118). Status and instruction registers. Zero flag is a _____ bit flag of 8086 . There are 8 general purpose registers in 8086 microprocessor. PROGRAMMING MODEL General Purpose Registers Special Purpose Registers Segment Registers 80386 and above:-32-bit registers (except seg. Flags Affected The floating point coprocessor became integrated on most versions of the 80486, rather than existing . Total number of . The Intel 80386, part 17: Future developments. However there are also special purpose registers. This register is addressed as either BP or EBP. 32-bit operands are always used with these instructions, regardless of the operand-size attribute. 80386 supports a variety of operating clock frequencies, which are 16 MHz, 20 MHz, 25 MHz, and 33 MHz. Architecture. 8086, 80286 Offset (32-bit) 80386 and above Purpose CS IP EIP Program SS SP, BP ESP, EBP Stack DS BX, DI, SI, . These registers They deal with selecting blocks (segments) of main memory. This unit has two separate units within it. Those are still important. As their name implies, they are the only registers that are general purpose: each has a set of conventional uses 1, but programmers are generally free to ignore those conventions and use them as they please 2.. Because x86-64 evolved from a 32-bit ISA which in turn evolved . Microprocessor 80386 1. The data buffers interface the internal data bus with the system bus. We can understand the concept of segments as Textbook pages. The Intel 80486 introduced pipelining and on-chip caching. • A 32 - bit register known as an extended register, is represented by the register name with prefix E. • Example : A 32 bit register corresponding to AX is EAX, similarly BX is EBX etc. Any attempt to use the registers for any other purpose may result in considerable grief, especially if you intend to move up to a better CPU like the 80386. Although processors still support them, the implementations are not optimized, and compilers don't generate them. b) Decoders. Two additional 16 bit segment are included FS and GS. On this channel you can get education and knowledge for general issues and topics The registers are like variables built in the processor. regs. . It holds an address bus of 32 bit. 12 Systems Design & Programming Microprocessor Architecture: Registers CMPE 310 Real Mode . )-Two additional segment registers:F,G. The 80386 (and later) processors provide 32 bit registers. Architecture of 80386 Microprocessor. • In real mode, the default operand size is 16 bit but 32- bit operands and addressing modes may be used with the help of override prefixes. • The segment size in real mode is 64k, hence the 32-bit effective addressing must be less than 0000FFFFFH.

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