Re: Apple II suicide--a sermon...

[toddpw@frappe.ugcs.caltech.edu (Todd P. Whitesel)]

jd-wong@uxa.cso.uiuc.edu (Jim Wong) writes:

>I'm intrigued.  I had no idea that the ARM chip was derived from the
>6502.  Is it binary compatible?  Could you build a 32-bit Apple II around it?

No. The ARM has 4 byte instructions. They get their instruction compactness
by incorporating some CISCy features, but mainly from having a sneaky ALU
setup that makes it easy to combine shifts with other instructions, and the
condition field that _every_ instruction has (technically every ARM
instruction is "if (condition) then execute else NOP") which makes short
conditional blocks much smaller and faster. (This is a concept which is
grudgingly being adopted by modern RISC chips in the US, and only for
parts of the instruction set, not as a global feature.)

The documented desire at ARM was that they wanted to design an architecture
which had the same spirit as the 6502. Binary compatibility was not an issue.

Todd Whitesel
toddpw @ ugcs.caltech.edu