Michael J Kingston wrote:
> In message <OTS8f.28348$Bv6.232@twister.nyroc.rr.com>, Peter Flass
> <Peter_Flass@Yahoo.com> writes
>
>>
>> sqrfolkdnc wrote:
>>
>>> Of course the LGP-30 had main memory AND the accumulator on DRUM, and
>>> addresses were NOT sequentially assigned. A good programmer located
>>> his working storage so that it could be most often fetched in the same
>>> revolution as the instruction, then fetch the next instruction wihout
>>> wasting a whole revolution of the drum. There was a chart showing what
>>> memory locations could be accessed from an instruction at any location,
>>> without losing a revolution. It had 4096 words of memory, IIRC.
>>>
>>
>> Sounds like the IBM 650.
>>
> My recollection is that IBM 650 drum had sequential addresses. Ferranti
> Pegasus drum had addresses in a sequence arranged so as to optimise
> continuous reading of 8-word blocks.

I think that's correct, but what I was alluding to was that each 650
instruction included the drum (disk?) address of the "next" instruction.
I guess it must have been quite an art to organize your program so that
the system was ready for the next instruction just as that location
passed under the R/W head so as not to lose a rotation.