Linked by Thom Holwerda on Wed 10th Dec 2008 22:52 UTC, submitted by teigetje
RISC OS And it seems as if another minor, barely-alive operating system will become encumbered by legal bickering between two small companies. The RISC OS scene, which is already a tangled and complicated mess of companies, version number teasing and incompatible versions, might be torn apart even further because RISCOS Ltd might take legal action trying to prevent RISC OS Open Ltd from releasing a RiscPC compatible ROM from the RISC OS 5 shared source project. Should you feel confused, you needn't worry: so does everyone else.
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RE: Futility
by steve_s on Thu 11th Dec 2008 11:59 UTC in reply to "Futility"
steve_s
Member since:
2006-01-16

This 26bit and 32bit is all about memory addressing and processor status flags.

Old ARM chips (ARM2, ARM3, and their bretheren) only supported 26bit addressing which severely limited how much memory they could support. There was a transition period when ARM chips supported both 26bit and 32bit addressing. Current ARM chips only support 32bit addressing.

The two addressing modes aren't entirely code compatible, since the original "26bit" ARM chips used bits in the program counter register (R15) as processor status flags. Those status flags were moved out of R15 when 32bit addressing was introduced, although the first chips supporting 32bit addressing would support a 26bit addressing mode which would ensure the status bits were still present in R15.

Some parts of RISC OS (and other code) relied on the presence of the status bits in R15, and thus that code was not 32bit-safe.

Reply Parent Score: 3

RE[2]: Futility
by memson on Thu 11th Dec 2008 13:46 in reply to "RE: Futility"
memson Member since:
2006-01-01

Memory addressing!! That's it!! I knew it was something silly like that.

Mind you, the Acrchies were always billed (to us students who used them by our teachers/professors) as being "32bit", as I guess the actual processor ran in a 32bit mode.

Reply Parent Score: 2

RE[3]: Futility
by Earl Colby pottinger on Thu 11th Dec 2008 14:49 in reply to "RE[2]: Futility"
Earl Colby pottinger Member since:
2005-07-06

Remember 26 bits = 64 million addresses. At that time Amiga was limited to 16 million, Atari for some odd hardware reason to even less. Mac were still at 16 million if I remember right.

And Intel machines were using all sorts of incompatible addressing scheme to break 1 million bytes.

Acorn and ARM users must have thought they had it made in the shade.

Reply Parent Score: 3