<pedrocorreia.net ⁄>
 

<How Computers Boot Up ⁄ >




clicks: 2939 2939 2008-07-28 2008-07-28 goto tecnologia myNews tecnologia  Bookmark This Bookmark This


Things start rolling when you press the power button on the computer (no! do tell!). Once the motherboard is powered up it initializes its own firmware - the chipset and other tidbits - and tries to get the CPU running. If things fail at this point (e.g., the CPU is busted or missing) then you will likely have a system that looks completely dead except for rotating fans. A few motherboards manage to emit beeps for an absent or faulty CPU, but the zombie-with-fans state is the most common scenario based on my experience. Sometimes USB or other devices can cause this to happen: unplugging all non-essential devices is a possible cure for a system that was working and suddenly appears dead like this. You can then single out the culprit device by elimination.

If all is well the CPU starts running. In a multi-processor or multi-core system one CPU is dynamically chosen to be the bootstrap processor (BSP) that runs all of the BIOS and kernel initialization code. The remaining processors, called application processors (AP) at this point, remain halted until later on when they are explicitly activated by the kernel. Intel CPUs have been evolving over the years but they're fully backwards compatible, so modern CPUs can behave like the original 1978 Intel 8086, which is exactly what they do after power up. In this primitive power up state the processor is in real mode with memory paging disabled. This is like ancient MS-DOS where only 1 MB of memory can be addressed and any code can write to any place in memory - there's no notion of protection or privilege.

Most registers in the CPU have well-defined values after power up, including the instruction pointer (EIP) which holds the memory address for the instruction being executed by the CPU. Intel CPUs use a hack whereby even though only 1MB of memory can be addressed at power up, a hidden base address (an offset, essentially) is applied to EIP so that the first instruction executed is at address 0xFFFFFFF0 (16 bytes short of the end of 4 gigs of memory and well above one megabyte). This magical address is called the reset vector and is standard for modern Intel CPUs.



este é só um excerto do artigo, para aceder ao artigo completo, clique no link em baixo:
this is just a small excerpt from the article, to access the full article please click in the link below:

http://duartes.org/gustavo/blog/post/how-computers-boot-up




Subscribe News RSS  Subscribe News Updates by E-mail





myNews <myNews show="rand" cat="tecnologia" ⁄>

MongoDb Architecture new ...

NOSQL has become a very heated topic for large web-scale deployment where scalability and semi-struc (...)

clicks: 16645 16645 2012-05-14 2012-05-14 goto url (new window) horicky.blogspo... goto myNews tecnologia


A Hopefully Fair and Useful Comparison of Haskell Web Frameworks new ...

Recently there has been a lot of discussion and questions about the differences between the big thre (...)

clicks: 13260 13260 2012-05-13 2012-05-13 goto url (new window) softwaresimply.... goto myNews tecnologia


Retina graphics for your website new ...

retina.js is an open source script that makes it easy to serve high-resolution images to devices wit (...)

clicks: 13109 13109 2012-05-11 2012-05-11 goto url (new window) retinajs.com/ goto myNews tecnologia


What every programmer should know about memory, Part 1 new ...

In the early days computers were much simpler. The various components of a system, such as the CPU, (...)

clicks: 14371 14371 2012-05-10 2012-05-10 goto url (new window) lwn.net/Article... goto myNews tecnologia


The State Of HTML5 Video

HTML5 has entered the online video market, which is both exciting and challenging for developers in (...)

clicks: 5441 5441 2012-02-14 2012-02-14 goto url (new window) longtailvideo.c... goto myNews tecnologia


A Tour of Amazon's DynamoDB

Amazon's recent release of DynamoDB, a database whose name is inspired by Dynamo, the key-value data (...)

clicks: 5208 5208 2012-02-13 2012-02-13 goto url (new window) paperplanes.de/... goto myNews tecnologia


Video: CSS3 Secrets: 10 things you might not know about CSS3

A number of prominent front-end developers delivered helpful talks at this year's Fronteers 2011 con (...)

clicks: 5741 5741 2011-11-30 2011-11-30 goto url (new window) css.dzone.com/a... goto myNews tecnologia


Google BigQuery Service: Big data analytics at Google speed

Rapidly crunching terabytes of big data can lead to better business decisions, but this has traditio (...)

clicks: 4870 4870 2011-11-30 2011-11-30 goto url (new window) googlecode.blog... goto myNews tecnologia