Programming Start Up

Dennis Ritchie. Creator or UNIX and C. The foundation for all programming languages and software systems in the world.

Operating System

A program that manages the software and hardware for the user. It was programmed to do repetitive tasks like managing files , hardware , running programs and receiving commands by the user. Interact with OS by an User Interface.

OS also manages the software applications.For a program to be used it must be loaded into a computer memory and then the instructions must be executed.

Light Bulb, switch on it will glow, switch off the bulb is off. Computer does pretty much same job except that it executes way more instructions , it has a processor and memory and storage units.

Mystery of Operating System

i was told about these so many times in college.Never did i learn. Reason is i can’ learn unless i want.The desire the passion and the effort has to come from inside.Only then when i learn it will stay.

when you switch on the button on the PC,BIOS ( Beginners Input Output System) is run , which is located on BIOS ROM.  BIOS has first set of instructions which goes like this, further to this these BIOS instructions are run by the processor.

-store instruction to power on in a memory address (POST – Power On Self Test). Any errors it will stop

-check CMOS RAM(very small battery is used to power it. it is battery powered such that it can hold the data even when switched off) CMOS has BIOS settings

-if no then battery Failure,then continue to initialize CPU

-check hardware like storage,video card,keyboard and mouse

once POST check are done then BIOS looks to find where to locate OS from the CMOS chip.In most PC the OS loads from C drive.

Once OS initializes , the BIOS copies its files into memory and the OS basically takes over of boot.From now ON OS will load all the drivers,system memory,devices etc.Once done the user can use the Applications.

there is a way to bypass few checks on BIOS which will help to boot fast, like Quick Power On Self Test

It is important to realize just how slow some of these devices are compared to the processor. Even the fastest hard disks have an access time measuring around 10 milliseconds. If it has to wait 10 milliseconds, a 200 MHz processor will waste 2 million clock cycles! And CD-ROMs are generally at least 10 times slower. This is why using caches to avoid accesses to these slow devices is so crucial.

Caching actually goes even beyond the level of the hardware. For example, your web browser uses caching itself, in fact, two levels of caching! Since loading a web page over the Internet is very slow for most people, the browser will hold recently-accessed pages to save it having to re-access them. It checks first in its memory cache and then in its disk cache to see if it already has a copy of the page you want. Only if it does not find the page will it actually go to the Internet to retrieve it.

windows key + pause break to open system properties

window key + E opens my computer

What does a Computer Science Engineer needs to know ?

some course , go home and check

above one is awesome

nice , it has harvard video site and few very useful links


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