OS-display

harpywarrenSoftware and s/w Development

Dec 14, 2013 (3 years and 10 months ago)

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1

OPERATING SYSTEMS. WHAT KINDS ARE THERE?


Real
-
time operating system (RTOS)



Control machinery, scientific instruments, industrial systems



Little user
-
interface capability, no end
-
user utilities



Operation executes in real time (precisely the same amount of
time every time it
occurs)


Single
-
user, single task



One user does one thing at a time



Palm handheld computers


Single
-
user, multi
-
tasking



Single user runs several programs at the same time



Desktop, laptop PCs



Microsoft Windows, Apple’s MacOS


Multi
-
user



S
everal different users run different programs



Unix, VMS (Virtual Memory System
, now OpenVMS
)


Multi
-
user OSs v. single
-
user OSs that support networking



Windows 2000 and Novell Netware (many networked users) not true multi
-
user OSs



System administrator is t
he only
user

for Windows 2000 or Netware



OS FUNCTIONS


When you switch on:



PC runs instructions kept in ROM =
POWER ON SELF TEST

(POST)



Checks CPU, RAM,
BIOS



BIOS is loaded into
main memory (
RAM
)
, activates disk drives



When the HD is activated the first
part of the OS is loaded =
bootstrap loader


Bootstrap loader loads rest of OS into RAM



Load small driver programs for hardware (leyboard, monitor)



Creates divisions of memory (for OS, applications, user info)



Hands over control of PC to OS


What the OS do
es



Processor management



Memory management



Storage management



Application interface



User interface


Processor management



Each process/application receives enough of CPU’s time



Process swapping
(more complicated for multi
-
tasking)


thrashing



Optimal use of
processor cycles for real time work


2



Process

or
thread



Background processes
: memory and disk management, virus protection….



Interrupts
: maskable v. non
-
maskable (NMIs)



Process control blocks
: data package containing state of program when switching, all
file
s being uses, etc.



More than one CPU:
asymmetric

v.
symmetric

OSs


Memory management



OS sets up
memory boundaries

for different applications



Applications loaded in block sizes (e.g. 2 KB)



Virtual memory management (blocks or pages)


Networks



Service packs
(Windows updates)



Netbooting
:

remote boot a PC over an IP network without access to hard disk, diskette
or CD (diskless or thin clients)



OPEN SOURCE




Threads are distinguished from traditional multi
-
tasking operating system processes in that
processes

ar
e
typically independent, carry considerable state information, have separate
address spaces
, and interact only through system
-
provided inter
-
process communication
mechanisms. Multiple
threads
, on the other hand, typically
share the state information of a
s
ingle process, and share memory and other resources directly