1979, INTEL introduced 8086/8088 chip, which still belongs to 16-bit microprocessor and contains 29,000 transistors. The clock frequency is 4.77MHz, the address bus is 20 bits, and 1MB memory can be used. 2 20 =1048576b =1MB memory space can be directly addressed. There are two 16 = 65536b = 64 KB I/O ports.
Extended data:
The 20-bit address bus of 8086/8088cpu, AD7~AD0 belong to 8-bit address/data bus, which is time division multiplexed, bidirectional and tri-state. A 15 ~ A8 belongs to the address line and has three-state output. A 19/S6 ~ A 16/S3 belongs to the address/status line, with time division multiplexing, output and three states. It is used as an address line in the state of bus cycle T 1, and A 19 ~ A 16 outputs the upper 4 bits of address.
It is used as a status line in T2~T4 state of bus cycle, and outputs status information in S6 ~ S3, where S6 is always 0. S5 indicates the current status of the interrupt enable flag. If S5 = 1, it indicates that the maskable interrupt request is currently allowed, and S5=0, all maskable interrupts are prohibited. S4 and S3 are used to indicate which segment register is being used.