The Kentucky Register

McVey Hall, Lexington, Kentucky 40506 Area Code 606 Phone 258-2900, Ext. 2963

May, 1968                                                         Vol.4, Issue 2
                               TIME SHARING
   "Time Sharing" is a term which has been  widely  used  in  computing  circles
lately.  It, like so many other computer-related terms, has various meanings all
of  which  relate  to  multiple  jobs somehow sharing computer facilities.  This
article attempts to clarify some  of  the  existing  confusion  concerning  this
concept  through  a  short,  simplified  discussion of various modes of computer
   Most computer  work  has  been  performed  in  a  mode  known  as  sequential
batch-processing,  whereby  jobs  composed  primarily  of  tabulating  cards and
magnetic tapes were presented to a computer and executed one-by-one,  until  all
jobs were complete.  Several difficulties existed with the sequential batch mode
of operation.  Three severe problems were:
       a.  A long running job road-blocked (prohibited) all other work until the
           long running job was completed.
       b.  Since  it  is  rare  that  any  single  job  uses all facilities of a
           computer system, idle facilities such as computer  memory  (storage),
           information  channels  or input-output devices were not available for
           other work.
       c.  Input and  output  generally  involve  reading  information  from  or
           writing   information   upon  media  controlled  by  relatively  slow
           electro-mechanical devices.  A printer is such a device; it can print
           at the rate of about 1000 lines of output per minute.  When  compared
           with  internal  processing  speeds  this  is  quite  slow:   the  IBM
           System/360 model 50 can execute about 10 million instructions in  one
           minute.   The computer, under sequential batch mode, was often slowed
           considerably each time it was required to perform input or output.
                            NEW COMPUTING CENTER SERVICES
                              ASSEMBLER G AVAILABLE
                                  NEW PERSONNEL
   The University of Kentucky Computing Center will soon implement a new control
program in OS/360 called MVT (Multiprogramming with a Variable number of Tasks).
The change-over should be transparent to most users in that programming  changes
will not be required and jobs which presently run under release 14 will also run
with  the  MVT  system.   A  few  minor  changes  in Job Control Language may be
required for some users.  Full information will be distributed well  in  advance
of  implementation.   The  same present restrictions will apply (e.g.  core size
limited to 157,000 bytes, restrictions on  printed  output,  job  running  time,
etc.).  In fact, the typical user will not really be concerned.  We release this
information for institutional, rather than programming purposes.
   MVT  will  provide  the  ability  to  execute  several  jobs  in the computer
simultaneously.  Presently, only two jobs (the user's problem program and  HASP)
simultaneously  reside in computer storage.  With MVT, we expect to run two user
problem programs simultaneously which will improve system efficiency.   The  MVT
control program operates the computer in a multiprogrammed batch mode (explained
elsewhere in this issue.)
                            IBM 360/50 RELEASES
            NEW COMPUTING CENTER PROJECTS (through February, 1968)

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