what are the advantages of 8086 over 8088?

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DevarenjiniP • 3.2k

Features of 8088 in comparison with 8086

All the changes in 8088 over 8086 are directly or indirectly related to the 8-bit, 8085 compatible data and control bus interface.
Nearly all the internal functions of 8088 are identical to 8086.
8-bit external data bus
- designed for internal 16-bit processing capability.
The 8088 uses the external bus in the same way as 8086,
- only 8 bits of external data are accessed at a time.
- While fetching or writing the 16-bit data, the task is performed in two consecutive bus cycles.
As far as the software is concerned, the chips are identical, except in case of timings.
The pre decoded code queue length is reduced to 4 bytes in 8088
- whereas the 8086 queue contains 6 bytes.
  - This was done to avoid the unnecessary pre-fetch operations and optimize the use of the bus by BIU while prefetching the instructions.
The 8088 bus interface unit will fetch a byte from memory to load the queue each time, if at least 1 byte is free.
- In case of 8086, at least 2 bytes should be free for the next fetch operation.
The overall execution time of the instructions in 8088 is affected by the 8-bit external data bus.
- All the 16-bit operations now require additional 4 clock cycles. The CPU speed is also limited by the speed of instruction fetches.
The pin assignments of both the CPUS are nearly identical, however, they have the following functional changes.
- A8-A5 already latched, all time valid address bus.
- BHE# has no meaning as the data bus is of 8-bits only.
- S,# provides the SO status information in minimum mode.
- 10#/M has been inverted to be compatible with 8085 bus structure

S.NO	8086 MICROPROCESSOR	8088 MICROPROCESSOR
1	The data bus is of 16 bits.	The data bus is of 8 bits.
2	It has 3 available clock speeds (5 MHz, 8 MHz (8086-2) and 10 MHz (8086-1).	It has 3 available clock speeds(5 MHz, 8 MHz)
3	The memory capacity is 512 kB.	The memory capacity is implemented as a singleIMX 8 memory banks.
4	It has memory control pin (M/IO) signal.	It has complemented memory control pin (IO/M)signal of 8086.
5	It has Bank High Enable (BHE) signal.	It has Status Signal (SSO).
6	It can read or write either 8-bit or 16-bit word at thesame time.	It can read only 8-bit word at the same time.
7	Input/Output voltage level is measured at 2.5 mA.	Input/Output voltage level is measured at 2.0 mA
8	It has 6 byte instruction queue.	It has 4 byte instruction queue as it can fetch only 1byte at a time.
9	It draws a maximum supply current of 360 mA.	It draws a maximum supply current of 340 mA

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