To understand the development of the various microprocessors, you have to put them into context both from the original design and intended market and from the actual mass production date. Also the competition from rival manufacturers.
This is the timeline that I have been working on:
1971 - Intel 4004 4 bit
1972 - Intel 8008 (originally the 1201) 8 bit
1974 - Intel 4040 4 bit (enhanced 4004)
1974 - Intel 8080 8 bit
1974 - Motorola 6800 8 bit
1975 - MOS 6501 8 bit
1975 - MOS 6502 8 bit (see notes below)
1976 - Zilog Z80 8 bit
1976 - Intel 8085 8 bit (followed by the 8085A, a bug fixed version)
1978 - Intel 8086 16 bit
1978 - Motorola 6809 8 bit
1979 - Intel 8088 16 bit but with a 8 bit data bus
1979 - Zilog Z8000 (Z8001, Z8002) 16 bit
1979 - Motorola 68000 16/32 bit but with a 16 bit data bus
1980 - Intel 8085AH (HMOS version of the 8085A)
1982 - Intel 80186 16 bit
1982 - Intel 80188 16 bit but with a 8 bit data bus
1982 - Intel 80286 16 bit
1982 - Motorola 68008 16/32 bit but with a 8 bit data bus
1982 - Motorola 68010 16/32 bit but with a 16 bit data bus
1982 - Hitachi 6309 8 bit CMOS, an enhanced version of the 6809
1982 - National Semiconductor 32016 32 bit but with a 16 bit data bus
1984 - Motorola 68012 16/32 bit but with a 16 bit data bus
1984 - Motorola 68020 32 bit
1984 - National Semiconductor 32032 32 bit
1985 - Intel 80386 32 bit
1985 - Hitachi HD64180 (enhanced Z80)
1985 - National Semiconductor 32332 32 bit
1986 - Zilog Z80000 32 bit
1987 - National Semiconductor 32532 32 bit
1987 - ARM2 32 bit
1987 - Motorola 68030 32 bit
1987 - Zilog Z280
1991 - Motorola 68040 32 bit
1994 - Motorola 68060 32 bit
1994 - Zilog Z380
2001 - Zilog eZ80 (enhanced Z80)
Note that the dates are wherever possible, dates when the first units were available, or announced as being available.
Others, but dates not yet known:
80C85A CMOS version of the 8085A
Zilog Z180 (enhanced Z80)(Z80180, Z8S180, Z8L180)
Zilog Z64180 (enhanced Z80)
Zilog Z320 ( CMOS version of the Z80000)
65xx, 65Cxx and 65SCxx processors
These versions were available:
6501
6502
6503
6504
6505
6506
6507
6512
6513
6514
6515
65C02
65C102
65C112
65SC02
65SC03
65SC04
65SC05
65SC06
65SC07
65SC12
65SC13
65SC14
65SC15
65SC102
65SC103
65SC104
65SC105
65SC106
65SC107
65SC112
65SC115
See also
https://en.wikipedia.org/wiki/Microprocessor_chronologyThe 6501 and 6502 objective was to be simple and inexpensive, with the expectation that the main market would be embedded applications.
It takes time to design and produce complex intergraded circuits. And MOS had to battle Motorola both in the market and in court. MOS were then bought by Commodore.
In the meantime, as you can see many other microprocessors were being developed and produced. The Zilog Z80A became the biggest competition to the 6502 not the Motorola 6800.
It was not only the producers of the 6502 that failed to make much of dent in the 16 bit and 32 bit markets. Zilog were also not very successful. Neither were National Semiconductor.
Apple with their Macintosh range used Motorola 68K (68000) processors.
In Europe, for home computers, Motorola with their 68000 were successful and around the world for business use, it was Intel with the 8086, and 8088. Then later the 80286 etc.
Once Microsoft MS-DOS running on IBM PCs (or compatibles) became a “standard”, any other architecture would be very, very difficult to become successful in the general computing market.
As well as all the 8 bit microprocessors, 16/32 bit microprocessors with 8 bit data busses and reduced address busses also provided competition in both home computers and in embedded applications.
Embedded applications were also the prime market for microcontrollers (and there is a vast range of these).
In such heavily competitive markets, it’s hard to successfully design, launch and market new microprocessors.
ARM were successful more through accident than design, as the ARM microprocessors could operate efficiently at low power. Exactly what you want from battery powered equipment that has to be pocket sized.
Mark