At start, no Operating Systems.
Computers are like the abstract model of a machine
in Automata theory.
Running one program and nothing else.
1 user (1 programmer) at a time
1 program at a time
Program has to finish before next program begins
Programmer operates machine alone:
Manually load program.
Run until crashed (dump memory and registers)
or finished (print output).
Revise program, run again, or run next program.
Interactive (great if you're the lone programmer).
But CPU idle for long periods
(e.g. while program being revised,
or when program halts/crashes when
programmer not watching).
Long wait to use machine for other programmers.
Driving forces for change:
Lots of programmers wanting to use machine.
Computers expensive (any CPU idle time bad).
(2) In 1950s-60s, Operator hired to run computer.
Programmers have to submit jobs, receive results later.
Operator schedules jobs.
Jobs still stored on sequential (tape) access
(no random access medium yet).
Sequential tapes of jobs are prepared by operator
for the CPU to run through once.
Resident monitor:
Software. Always in memory (first OS).
Doesn't decide order of jobs,
but does co-ordinate their sequencing,
automatic starting and terminating.
Programming with an Operator controlling what runs:
Long queues, not interactive.
If error in program may have to wait days to retry it.
Have to think things through in advance!
A program written in the language
PL/I
on punch cards
around 1969.
From here.
Driving force for change:
Random access permanent storage medium (disk) becomes available.
(3) Pool of jobs on disk, random access.
OS can now implement the human operator's algorithms
in deciding sequence of jobs to run.
Scheduling of jobs now totally automated (true OS).
Driving force for change:
Programs read from and write to disk and other devices.
I/O device speed is much slower than CPU speed,
so CPU still often idle while I/O going on.
(4) Some parallelisation of I/O and computation.
Device controller is a piece of hardware
that can work in parallel with the CPU. Not a parallel computer
- it is just a specialised device for data transfer,
not a general-purpose computer.
Example:
Spooling - Print device controller is
still copying data from disk to printer
while CPU has already begun working on next job.
Next job can begin while previous is still printing out.
Driving forces for change:
Wait times still too long.
Long jobs delay everything else. Could delay other jobs by hours.
Program might do I/O half-way through
its execution (rather than only at start/end).
When program stops for this I/O, CPU is idle.
(5) Multi-programming.
A series of breakthroughs:
Multiple jobs in memory (and running) at the same time.
Each memory space protected from each other.
OS picks one, executes it for a while, stops
(e.g. when program waits for input, or else randomly),
picks other to run.
Driving forces for change:
The above is still a batch model (program runs, lots of I/O with devices, exits)
not interactive programs (no "user interfaces" invented yet).
But now the program could be waiting on user input.
Which could be a wait of hours, but that does not matter now.
Users could now interact with programs while they are running.
Computers cheaper - cheap dumb terminals available.
Humans' time is expensive - don't want them to wait.
(6) 1970s-80s. Interactive time-sharing on mainframes.
Multi-programming where the program may be waiting on a user.
OS will in the meantime service another program,
which may be interacting with another user.
Result: Multiple users share the CPU.
If the time-slicing is quick enough, they all feel
as if they have their own dedicated machine!
CPU kept busy.
Programmers happy. They can now revise their code and quickly run it again without waiting.
Above all:
User interaction at run-time allows a whole world of programs
that were never possible before.
"ls" and all the rest.
The "listf" command (1961),
the ancestor of "ls" (1971).
DEC
VT100
terminal (1978).
This kind of computer terminal would be
used to run programs on a mainframe
shared with other users.
Users can now interact with programs at run-time!
Driving forces for change:
Real computers (not dumb terminals) get cheap.
(7) 1980s. Standalone PCs.
The dream at last of a real computer for every user.
An odd era, by modern standards.
Because
no network.
Internet not yet important.
The user alone with their PC.
Users no longer
logging in to mainframes.
Few clashes with other users.
Multi-programming mainly used so single user can run multiple programs at same time.
The standalone PC world of
DOS:
First generation IBM PC (1981).
From here.
The standalone PC world of
early
Windows:
Clip shows
Solitaire,
bundled with Windows from 1990.
- How office workers wasted time on PCs before the Internet.
Driving forces for change:
Internet becomes usable and useful.
(8) 1990s. Internet.
Web is killer app for Internet 1993.
Return to sharing with multiple users in access to mainframe
- this time access to shared remote web server.
Web server has to time-slice many clients' requests, overlapping in time,
again using multi-programming concepts.
The shared mainframe returns:
The Web explodes in 1993, and has changed everything by the end of the 1990s.
Driving forces for change:
Broadband.
Smartphones.
(9) 2000s
Broadband at home:
New technologies enable broadband at home (replacing dialup).
Enables multimedia Internet:
Multimedia - video, audio, photo.
YouTube (2005) probably the defining application of 2000-10 period.
Smartphones:
Growth in mobile network capacity enables Internet on smartphones.
After many experiments, multi-touch explodes to take over smartphone Internet access:
Mobile - Internet on mobile devices.
Proper OSes on mobile devices (proper mini-computers).
iPhone (2007) probably the defining invention of 2000-10 period.
The decline of dialup, 2006-08 (in Ireland).
The mobile world before 2005:
No or limited Internet.
Image from here.
The greatest product launch ever?
Steve Jobs introduces the iPhone
at MacWorld 2007.
The modern mobile world begins.
Click through to video.
Go to 5:20 where he introduces the modern concept of multi-touch,
which had a
history
but went mainstream with the iPhone.
Ancient Brain
