🚀 go-pugleaf

In article <1355830485.555945700.866...@news.eternal-september.org>,
Peter Flass  <peter...@yahoo.com> wrote:
>> We all think it's obvious to have byte/word addressing where the word
>> addresses are byte addresses with the low bits zero, but it wasn't
>> obvious at all before IBM invented it for the 360.  Once they had a
>> memory architecture that could work either way, building the
>> instruction set wasn't so hard.
>
>Or maybe not so obvious. With word addresses you can address a lot more
>memory with a given-length address field. A lot of machines, like the
>PDP-10, solved this problem by having byte instructions use a byte pointer
>that indicated the byte within the word, and this worked well.

That's right.  I know of a similar character addresssing kludge in the
GE 635.  It was OK, but the profusion of byte instructions added to
the later models of -10 suggest that it didn't work that well.

The 360 design was clever that the addresses in the architecture were
big but base registers kept the instructions were small, so only the
registers had to be 32 bits.

>> That too, although BOS, TOS, DOS, OS/PCP, OS/MFT, OS/MVT, CP/CMS, TSS,
>> and PS44 suggest that consolidating the system software didn't work
>> out so well.
>
>PS44, TSS, and CP/CMS were special cases. PS/44 was a special case, since
>the /44 used the same platter disk as the 1130 (2315?), and no other 360
>supported it. Also it was designed to be a real-time OS, whereas real-time
>features were grafted on to OS/360 later. 

More to the point, the /44 only implemented a subset of the 360's
instruction set, so even with different peripherals it couldn't run
any other OS.

>All the rest other than OS were mistakes. IBM was unable to get
>even PCP to fit on the smallest machines, so DOS, TOS, BOS were written as
>"temporary" systems which became permanent.

Yes.  I never entirely understood the difference between BOS and DOS.
I realize that BOS could run in 8K and DOS needed 16K, but what else
did BOS leave out?

-- 
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John Levine, jo...@iecc.com, Primary Perpetrator of "The Internet for Dummies",
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