🚀 go-pugleaf

In article <1498@dg_rtp.UUCP>, meissner@dg_rtp.UUCP (Michael Meissner) writes:
  In article <5954@amdahl.UUCP> chuck@amdahl.UUCP (Charles Simmons) writes:
  > In article <3436@iuvax.UUCP> bobmon@iuvax.UUCP (Che' Flamingo) writes:
  > >davidsen@kbsvax.steinmetz.UUCP (William E. Davidsen Jr) writes:
  > >>
  > >>etc. The 68020 and 80386 have enough power to run large
  > >>businesses, schools, city and county government, etc.
  > 
  > Kinda makes you wonder why the Fortune 500 spends on the order of
  > $5,000,000 for an IBM mainframe or Amdahl mainframe when 68020
  > based workstations can be had for on the order of $50,000.
  
  While the 68020, 80386 (and whatever the latest 32*32 National makes) are
  fine in their niches, they are not up to the task of running a moderately
  large business.  Yes the address space is reasonable, but that is not all
  that goes into making a computer.  Ever see a DASD disk farm?  (a disk farm
  is a roomful of large disk drives, and possibly a larger room behind it of
  cartridges, tapes, etc -- these things store massize amounts of data).  The
  thing that the big guys specialize in is I/O -- with intelligent controllers
  [channels] offloading the main CPU.  I seriously doubt a 68020 workstation
  could put 100 or so 500M disk drives on it (or if you could, what the response
  time would be).  Data General is a supermini maker, and the largest disk
  configuration we support is on the order of 15 gigabytes (it may be higher or
  lower, but that is a ballpark figure).  That is a small compared to the large
  mainframes (it also costs near $1M just for the disks, not to mention the
  processor needed to support those disks).

Well, a good example of what Michael is saying is the pre-180 level Cybers.
These are *very* quick machines (a low level one can get something like 3 or
4 MegaFlops), but the CPU does almost no I/O at all.  There is, outside the
computer, somewhere between 4 and 20 PPU's (Peripheral Processer Units),
which are true computers themselves, which handle all of the I/O.  All the
computer does is put a call in its memory space (usually, probably even
always, location 1), and then the PPU sees it, and away it goes.  If you
need to wait for the data (which you usually do), you force a context switch
(save all the registers in a relatively short period of time, load the
registers from the last time System allowed a job to run, let it decide what
to do), and next time you run, you have your data.
Only saving grace on a machine running NOS....

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