COS 109 Monday October 19
• Housekeeping
– Problem Set 5 and Lab 4 are available
Problem Set 5 due after break!!
– Midterm next week
90 minutes to take it
No class next Wednesday (can do midterm here then)
Will be available from Wednesday 1201 AM to Friday 1159PM on blackboard
Midterm review Next Monday (10/26) at 7PM in room to be announced
– Problem Set 3 returned today
Second part of second problem caused some problems (adding numbers as you count down)
Fibonacci problem seems to have been very challenging (flow chart easier than actual coding)
• Today’s class
– Programming languages (continued)
– Software we depend on
The operating system
The file system
The cloud
Grades on Problem Set 3
35
30
25
20
15
10
5
0
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
Graded out of 30; average score 24.5
If you didn’t hand it in or scored below 15, you may want to talk to me
Evolution of programming languages
• 1940's: machine level
– use binary or equivalent notations for actual numeric values
• 1950's: "assembly language"
– names for instructions: ADD instead of 0110101, etc.
– names for locations: assembler keeps track of where things are in memory;
translates this more humane language into machine language
– this is the level used in the "toy" machine
– needs total rewrite if moved to a different kind of CPU
• Late 1950’s – Fortran and Cobol (first higher level languages)
• 50’s into 60’s – Algol, Basic and LISP
• 1970’s – C
C code compiled to assembly language
#include <stdio.h>
main() {
int num, sum = 0;
while (scanf("%d", &num) != -1
&& num != 0)
sum = sum + num;
printf("%d\n", sum);
}
(x86, Mac)
Ltmp2:
movl $0, -8(%rbp)
movl $0, -12(%rbp)
jmp LBB1_2
LBB1_1:
movl -12(%rbp), %eax
movl -8(%rbp), %ecx
addl %eax, %ecx
movl %ecx, -8(%rbp)
LBB1_2:
leaq -12(%rbp), %rax
xorb %cl, %cl
leaq L_.str(%rip), %rdx
movq %rdx, %rdi
movq %rax, %rsi
movb %cl, %al
callq
_scanf
movl %eax, %ecx
cmpl $-1, %ecx
je
LBB1_4
movl -12(%rbp), %eax
cmpl $0, %eax
jne LBB1_1
LBB1_4:
C code compiled to assembly language
.LL2:
#include <stdio.h>
main() {
int num, sum = 0;
while (scanf("%d", &num) != -1
&& num != 0)
sum = sum + num;
printf("%d\n", sum);
}
.LL3:
add
sethi
or
mov
call
mov
cmp
be
ld
cmp
be
ld
ld
add
st
b
sethi
or
ld
call
mov
ret
(SPARC)
%fp, -20, %g1
%hi(.LLC0), %o5
%o5, %lo(.LLC0), %o0
%g1, %o1
scanf, 0
%o0, %g1
%g1, -1
.LL3
[%fp-20], %g1
%g1, 0
.LL3
[%fp-24], %g1
[%fp-20], %o5
%g1, %o5, %g1
%g1, [%fp-24]
.LL2
%hi(.LLC1), %g1
%g1, %lo(.LLC1), %o0
[%fp-24], %o1
printf, 0
%g1, %i0
Sun SPARC
.LL2:
.LL3:
add
sethi
or
mov
call
mov
cmp
be
ld
cmp
be
ld
ld
add
st
b
sethi
or
ld
call
mov
ret
vs
%fp, -20, %g1
.L2:
%hi(.LLC0), %o5
%o5, %lo(.LLC0), %o0
%g1, %o1
scanf, 0
%o0, %g1
%g1, -1
.LL3
[%fp-20], %g1
%g1, 0
.LL3
[%fp-24], %g1
[%fp-20], %o5
%g1, %o5, %g1
%g1, [%fp-24]
.LL2
%hi(.LLC1), %g1
.L3:
%g1, %lo(.LLC1), %o0
[%fp-24], %o1
printf, 0
%g1, %i0
Intel x86
leal
movl
movl
call
-4(%ebp), %eax
%eax, 4(%esp)
$.LC0, (%esp)
scanf
cmpl
je
cmpl
je
$-1, %eax
.L3
$0, -4(%ebp)
.L3
movl
leal
addl
jmp
-4(%ebp), %edx
-8(%ebp), %eax
%edx, (%eax)
.L2
movl
movl
movl
call
leave
ret
-8(%ebp), %eax
%eax, 4(%esp)
$.LC1, (%esp)
printf
Evolution of programming languages, 1980's
• "object-oriented" languages:
C++
– better control of structure of really large programs
better internal checks, organization, safety
– a program ("compiler", "translator") converts into assembler or C
– enormous advantages:
portable: same program can be translated for different machines
faster, cheaper hardware helps make this happen
#include <iostream>
main() {
int num, sum = 0;
while (cin >> num && num != 0)
sum += num;
cout << sum << endl;
}
Bjarne Stroustrup, creator of C++
"C makes it easy to shoot yourself in the foot;
C++ makes it harder, but when you do it blows
your whole leg off."
Evolution of programming languages, 1990's
• "scripting", Web, component-based, ...:
Java, Perl, Python, Ruby, Visual Basic, Javascript, ...
– write big programs by combining components already written
– often based on "virtual machine": simulated, like fancier toy computer
– enormous advantages:
portable: same program can be translated for different machines
faster, cheaper hardware helps make this happen
var sum = 0; // javascript
var num = prompt("Enter new value, or 0 to end")
while (num != 0) {
sum = sum + parseInt(num)
num = prompt("Enter new value, or 0 to end")
}
alert("Sum = " + sum)
Javascript
• JavaScript, not to be confused with Java, was created in 10 days in
May 1995 by Brendan Eich
James Gosling, creator of Java
Separated at birth?
(James Gosling, creator of Java)
Programming languages in the 21st century?
• new general-purpose languages
– Go, Rust, Swift, Scala, ...
• ongoing refinements / evolution of existing languages
– C, C++, Fortran, Cobol all have new standards in last few years
• specialized languages for specific application areas
– e.g., R for statistics
• old languages rarely die
– it costs too much to rewrite programs in a new language
• Ultimately, natural language
Most popular programming languages
Trending languages
from http://spectrum.ieee.org/static/interactive-the-top-programming-languages2015#index/2015/1/1/1/1/1/50/1/50/1/50/1/30/1/30/1/30/1/20/1/20/1/5/1/5/1/20/1/100/
Website of the day
• Sorting algorithms choreographed
Software systems and issues
• operating systems
– controlling the computer
• file systems and databases
– storing information
• applications
– programs that do things
• cloud computing, virtual machines, platforms
– where boundaries become even less clear
• intellectual property
– copyrights, patents, licenses
• interfaces, standards, antitrust
– agreements on how to communicate and inter-operate
• open source software
– freely available software
Operating system
• a program that controls the resources of a computer
– interface between hardware and all other software
• runs other programs ("applications", your programs)
• manages information on disk (file system)
• controls peripheral devices, communicates with outside
• provides a level of abstraction above the raw hardware
– makes the hardware appear to provide higher-level services than it
really does
– makes programming much easier
Examples of Operating system
• DOS, Windows 3.0/3.1/95/98/NT/ME/2000/XP/Vista/7/8/10
Unix/Linux, Mac OS X, iOS, Android, ...
Mac OS X 10.0
Cheetah
24-Mar-01
Mac OS X 10.1
Puma
25-Sep-01
Mac OS X 10.2
Jaguar
24-Aug-02
Mac OS X 10.3
Panther
24-Oct-03
Mac OS X 10.4
Tiger
29-Apr-05
Mac OS X 10.5
Leopard
26-Oct-07
Mac OS X 10.6
Snow Leopard
28-Aug-09
Mac OS X 10.7
Lion
20-Jul-11
OS X 10.8
Mountain Lion
25-Jul-12
OS X 10.9
Mavericks
22-Oct-13
OS X 10.10
Yosemite
16-Oct-14
What's an operating system?
"Operating system" means the software code that, inter alia,
(i) controls the allocation and usage of hardware resources
(such as the microprocessor and various peripheral devices) of
a Personal Computer, (ii) provides a platform for developing
applications by exposing functionality to ISVs through APIs,
and (iii) supplies a user interface that enables users to access
functionality of the operating system and in which they can
run applications.
US District Court for the District of Columbia
Final Judgment, State of New York, et al v. Microsoft Corporation
November 1, 2002
ISV = Independent Software Vendors
API = Application Program Interface
History of general-purpose operating systems
•
•
1950's: signup sheets
1960's: batch operating systems (largely IBM)
– operators running batches of jobs
– OS/360 (IBM)
•
1970's: time-sharing (minicomputers e.g. Digital Equipment Corporation)
– simultaneous access for multiple users
– Unix (Bell Labs; Ken Thompson & Dennis Ritchie)
•
1980's: personal computers, single user systems
– DOS, Windows, MacOS
– Unix
•
1990's: personal computers, PDA's, …
– PalmOS, Windows CE, …
– Unix / Linux
•
2000's: Windows vs. Unix/Linux?
– MacOSX is a Unix system
•
2010's: Apple vs. Google
•
not all computers have general-purpose operating systems
– iOS, Android, Chrome-OS, … (Unix/Linux-based)
– "embedded systems": small, specialized, but increasingly general
Unix operating system
• developed ~1971 at Bell Labs
– by Ken Thompson and Dennis Ritchie
• clean, elegant design
– at least in the early days
• efficient, robust, easy to adapt, fun
– widely adopted in universities, spread from there
• written in C, so easily ported to new machines
– runs on everything (not just PC's)
• influence
–
–
–
–
–
languages, tools, de facto standard environment
supported minicomputer manufacturer (Digital Equipment)
rewritten at UC Berkeley to be in public domain
enabled workstation hardware business (e.g., Sun Microsystems)
supports a lot of Internet services and infrastructure
often Linux
Ken Thompson and Dennis Ritchie
(circa 1972)
"It's a Unix system. I know this."
http://www.youtube.com/watch?v=dFUlAQZB9Ng
Linux
• a version of Unix written from scratch
– by Linus Torvalds, Finnish student (started 1991)
• source code freely available (kernel.org)
–
–
–
–
large group of volunteers making contributions
anyone can modify it, fix bugs, add features
Torvalds approves, sets standard
commercial versions make money by packaging and support,
not by selling the code itself
• used by major sites, including
– Google, Amazon, Facebook, Twitter, YouTube, ABC, CBS, CNN, ...
and www.microsoft.com, www.apple.com, itunes.apple.com, …
User experience at the computer
• You turn it on
– System boots
First the hardware, then the Windows operating system
– Your desktop appears
First icons, then applications
– Interaction devices can be used
Machine is listening to mouse, keyboard, etc.
– Machine enters new version of the fetch/execute cycle
Machine fetches command from user
Machine executes commands
What happens when machine boots
• Power goes on, each device is turned on
• BIOS lets you talk to hardware
– Change order devices are turned on
– Set system clock
– Identify new interaction devices
• Then, the boot program for Windows starts
– You tell it an order in which to look at disks
– It looks at disks in this order to find operating system
• Operating system boots
– Simple program called the operating system kernel is loaded (at
location 10). This is the program that runs the computer.
Operating system kernel
• Kernel
– Starts
Device drivers
Talk to RAM, disks, CD/ROM, …
Starts subsystems
memory management system (to organize data on RAM)
file system (to organize files on disk)
Gets user started
Starts window manager or creates a shell
Starts fetch/execute cycle
Fetch/execute cycle
• Fetch is Event driven
• Execution is done by the operating system
Fetching
• Fetch is Event driven
– The window manager listens for an event
From keyboard
Key down/key up
From mouse
Mouse motion, mouse button up or down
From other device
Game controller
Speech interface
Fetching (cont.)
• Identify where the command occurred
– In which window on the screen
• Identify the action that must be taken
– Examples
Type text into Word window
Click command in window of executing program
Click on resize corner of window
Click on icon from window
Click on icon from task bar