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Intel 8086 and 8088

What is the use of the extra segment in a 8086 processor?

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2005-10-26 10:23:08
2005-10-26 10:23:08

extra segment is a 16-bit register containing address of 64KB segment, usually with program data. By default, the processor assumes that the DI register points to the ES segment in string manipulation instructions. ES register can be changed directly using POP and LES instructions. It is possible to change default segments used by general and index registers by prefixing instructions with a CS, SS, DS or ES prefix. any corrections most welcome

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test is used by 8086 to check whether 8087(co-processor) is ready or busy..

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Memory segmentation in the 8086/8088 is used to allow the processor to access more than 64kb of memory, even though it is only a 16-bit processor. Each segment register allows access to one of 64k 64kb segments, each overlapping by 16 bytes, with the total addressibility being 1mb.

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Because that's the way Intel designed it. A segment register is 16 bits. That is 65536, or 64K, different values. Also, the processor is a 16 bit processor, and offset values can only contain 65536, or 64K, different values.

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In real mode it handle automatic through the use of an internal machine together with the segment register.

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In the 8086 microprocessor, the Code Segment (CS) register contains the paragraph address that will be added to the Instruction Pointer to obtain the address of the next instruction. Similarly, the Data Segment (DS) register contains the paragraph address that will be added to the Effective Address that is computed to find the address of the data used by that instruction. There are segment override prefixes, but the default use is CS for instructions and DS for data.'normal' address space in 8086 is 16 bit r which allows it to address 64k of linear memory space. Using segment registers to select a 'bank of memory' the CPU can use much more (20 bit addressing space)

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There are four segment registers in the 8086/8088 processor, CS, DS, ES, and SS, also known as Code Segment, Data Segment, Extra Segment, and Stack Segment. Any time an address is generated by the processor, it is added to the value of one of the segment registers, after that segment register is effectively multiplied by 16, or left shifted four bits, in order to generate the physical address that accesses memory. This gives an effective address range of 20 bits, or 1mb, but note that only 64kb is addressable through any segment register at one time, unless you stop to change the contents of that segment register. This is known as a segmented architecture. By default, the CS register is used when fetching instructions, the DS register is used when accessing data, the SS register is used when accessing the stack, and the ES register is used during certain string type instructions. If desired, an instruction prefix can be used to override, such as forcing use of CS instead of DS when using a table contained within opcode space.

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Because IBM wanted to build a computer with an 8-bit data bus. The 8086 and 8088 are the same processor, with the 8086 running on a 16-bit data bus, and the 8088 running on an 8-bit data bus. This allowed IBM to make the most use of older designs that supported 8-bit data buses, such as the 8080, the 8085, and the Z80.

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To increase the speed of the 8086, you need to increase the clock speed, reduce the number of wait states, or both. You could also optimize your code so that it runs faster. Since the 8086 is a segmented memory architecture, it is more efficient to use operands in one segment and to make near references to them.

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There were about 20,000 active transistors in the 8086.

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The 8088 is an 8 bit bus implementation of an 8086, which is a 16 bit processor. The reason for providing the 8088 variant is simply to minimize the hardware cost and complexity of designing a system to use the 8088. This is the approach used for the first IBM PC. Some implementations, such as the Tandy 1000SX, used the 80186, a highly integrated version of the 8086, in a 16 bit bus configuration. Later versions, in order to increase performance, went ahead and provided 32, 64 and 128 bit bus implementations of advanced processors.And, no, the 8086 is not a multiprocessing computer. It is a single processor. Intel did not get into multiprocessing until the Xeon and the Pentium IV.

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Maybe you mean the prefetch queue?

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Every computer needs a processor. The machine was designed to be a good processor of waste paper.


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