November 3, 2024

Sun 3/80 -- The 68000 family

The Sun 3/80 uses the Motorola MC68030 chip. Most Sun 3 machines used the MC68020. A few rare early Sun machines (the Sun 2) used the MC68000.

Look at that 1989 date code!

MC68000

The 68000 came out in 1979 with 68,000 transistors. It was really a 16 bit processor (it had a 16 bit ALU), but presented a 32 bit programming model. The usual clock was 8 Mhz, but 10 Mhz was common. Speeds up to 16 Mhz were available, but unusual. The 68000 had a minor variant, the MC68010. The 68010 added a VBR (vector base register). By making some small changes, the 68010 was able to support virtual memory. A 10 Mhz 68010 system was generally considered to be a 1.0 MIPS machine. The 68000 was the first microprocessor to make extensive use of microcode.
It was a wonder for its time.

The 68000 had a 16 by 16 bit multiply and a 32 by 16 divide.

MC68020

The 68020 came out in 1984. It has 200,000 transistors. It was a true 32 bit chip and added a 256 byte instruction cache. It had a 32 bit external bus, a 32 bit address bus, and supported an interface to a floating point coprocessor. It was made in speeds up to 33 Mhz.

The 68020 added a number of instructions. It had a 32 by 32 bit multiply as well as a 64 by 32 bit divide. It had additional addressing modes and some other instructions. Appendix E of the 68020 users manual gives a list of the new instructions and addressing modes.

MC68030

The 68030 came out in 1986. It has 273,000 transistors. It was available in faster speeds than the 68020 and above all included an MMU on chip. It also had a 256 byte data cache, which gave a signficant performance improvement. It was made in speeds up to 50 Mhz.
My sun 3/80 has a 20 Mhz chip.

The 68030 was faster at the same clock as the 68020. The fist Macintosh II used the 020 at 16 Mhz and gave 2.6 MIPS. The Macintosh IIx with the 030 at the same 16 Mhz clock gave 3.9 MIPS.

The 68030 might have had more lasting impact if it was not for the advent of much faster RISC processors like the Sparc, MIPS, and others.

MC68040

This integrated the math coprocessor on the chip.