AN-001: 65xx, x86, and 68K Instruction Level Performance Comparisons

Did you ever wonder why the popular early PC's (Apple, Acorn, Atari, and Commodore) and video games (Atari, Commodore, and Nintendo) were built on 65xx technology rather than on Intel x86 or Motorola/Freescale 68K technology?

Take a look at the 65xx 8-bit and 8/16-bit microprocessor execution speeds on an 8-bit data bus in the table below compared to the Intel x86 and Motorola MC68000. Now you know! Also, the performance of the x86 and the 68K were on a 16-bit data bus! The PC (x86) and Mac (68K) ran less than 8MHz memory bus speed when first introduced.

Comparison of Execution Speeds in Microseconds
at 8MHz Operating Frequency

Operation	Data Type	WDC 65C02S	WDC 65C816S	Intel x86	Motorola MC68000
Register to register move	Byte/word double word	0.25/0.50 1.00	0.25/0.25 0.50	0.25/0.50 0.50	0.50/0.50 0.50
Memory to register move	Byte/word double word	0.38/0.75 1.50	0.38/0.50 1.00	2.12/2.12 4.25	1.50/1.50 2.00
Add memory to register	Byte/word double word	0.38/0.75 1.50>	0.38/0.50 1.25	4.37/4.37 8.75	2.50/2.50 3.75
Compare memory to memory	Byte/word double word	0.75/1.50 3.00	0.75/1.00 2.00	2.25/2.25 4.50	1.50/1.50 2.25
Conditional branch	branch taken not taken	0.38 0.25	0.38 0.25	1.00 0.50	1.25 1.00
Modify Index branch if zero	branch taken	0.62	0.62	1.37	1.25
branch to subroutine	branch taken	0.75	0.75	2.37	2.25
Interrupt latency	Interrupt	1.25	1.50	22.75	21.75

Comparison of Execution Speeds in Seconds at 8MHz Operating Frequency

Operation	Data Type	WDC 65C02S	WDC 65C816S	Intel x86	Motorola MC68000
Sieve of Eratosthenes	N/A	N/A	.78	1.90