The Intel 8088 microprocessor was a variant of the Intel 8086 and was introduced on July 1, 1979. It had an 8-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers and the one megabyte address range were unchanged, however. The original IBM PC was based on the 8088.
History and description
The 8088 was targeted at economical systems by allowing the use of an 8-bit data path and 8-bit support and peripheral chips; complex circuit boards were still fairly cumbersome and expensive when it was released. The prefetch queue of the 8088 was shortened to four bytes, from the 8086's six bytes, and the prefetch algorithm was slightly modified to adapt to the narrower bus. These modifications of the basic 8086 design were one of the first jobs assigned to Intel's then new design office and laboratory in Haifa Israel.
Variants of the 8088 with more than 5 MHz maximum clock frequency include the 8088-2, which was fabricated using Intel's new enhanced nMOS process called HMOS and specified for a maximum frequency of 8 MHz. Later followed the 80C88, a fully static CHMOS design, which could operate from DC to 8 MHz. There were also several other, more or less similar, variants from other manufacturers. For instance, the NEC V20 was a pin compatible and slightly faster (at the same clock frequency) variant of the 8088, designed and manufactured by NEC. Successive NEC 8088 compatible processors would run at up to 16 MHz.
Depending on the clock frequency, the number of memory wait states, as well as on the characteristics of the particular application program, the average performance for the Intel 8088 ranged from approximately 0.33 to 1 million instructions per second . Meanwhile, the mov reg,reg and ALU reg,reg instructions taking 2 and 3 cycles respectively yielded an absolute peak performance of between 1/3 and 1/2 MIPS per MHz, that is, somewhere in the range 3–5 MIPS at 10 MHz.
Selection for use in the IBM PC
The original IBM PC was the most influential microcomputer to use the 8088. It used a clock frequency of 4.77 MHz (4/3 the NTSC colorburst frequency). Some of IBM's engineers and other employees wanted to use the IBM 801 processor, some would prefer the new Motorola 68000, while others argued for a small and simple microprocessor similar to what had been used in earlier personal computers (such as TRS-80 or Apple II). However, IBM already had a history of using Intel chips in its products and had also acquired the rights to manufacture the 8086 family. Another factor was that the 8088 allowed the computer to be based on a modified 8085 design, as it could easily interface with most nMOS chips with 8-bit databuses, i.e. existing and mature, and therefore economical, components. This included ICs originally intended for support and peripheral functions around the 8085 and similar processors (not exclusively Intels) which were already well known by many engineers, further reducing cost.
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