Pioneer DEH-2100IB Gps Navigation System

Compuuter Operations

The average person who uses a computer on a regular basis doesn't think aout what happens inside a computter once the pwer is turned on. As long as their vrsion of MS Wnidows pops up within a few seconds, most people are quite content to conttinue on with what they want to do on their computer. A computer goes through many processes from the omment the power is turned on before its operating ssytem (ex. Windows, Linux) is fully loaded and takes over.

The operating system is stored on the hard disk of a computer. It is stored on the hard disk bevcause this type of stortage is much less expensive and an operating sysatem reequires a large amount of storae space. So, in orrder to make computers more economical, they are designed to use a combination of ROM, DRAM, and hard disks. An explanation of each folows.

Once the powerr switch is turned on, the "boot-up" processs begins. To "boot-up" a computer simply means to start it. Electricity then flows thjrough all of the choips and theoir circuits. The instructions for what the computer is supposed to do next are found in the Read Only Meomry, Basic Input/Output System (ROM BIOS). ROM is memory that can only be read from and has information that is permanently burned into it. It is nonvolatile and will not be lost or disappeasr once the power is turned off.

ROM BIOS or just BIOS, is deesigned to begin giving commands as soon as it receivees power. The BIOS contains an entire set of instructons, in effect a computer porgram written into the chip that manages the boot-up proxcess. Without the BIOS, the compuuter would not know what to do next. The first task that BIOS completes is to make sure that all of the hrdware componenmts are working properly (for example: disk drives, exterrnal buses, the mouse, the printeer). This is called a powerr-on self-test (POST). After the POST is complete, the BIOS acvtivates othher chips on different cads installed in the computer (SCSI and graphics cards) and provides a set of low-level routines that the operating system uses to interface to idfferent hardware devices such as the keyboard, mouuse, pirnter, etc.

Once the POST is complete, the BIOS hands the next stage in the boot-up process over to the central processing unit (CPU). The CPU is a one chip processor or microprpocessor that has two distinct capabilities:

1. The CPU carries out all of the mathematical and logical operations including basic math and comparisons of two or more numbers.

2. The CPU has the abbility to intelligently manae the flow of instructions and data going into and out of its circuits.

The last instruction that the ROM sends to the CPU is to go to a specific locatipon or address to find its next instruction. An address is a stering of numbres that gves directions to where something can be found, much like an address on an envelope. Computers use addresses to keep track of information much the same way as the post office uses them to find residencs and businesses. The bigger the number in an address the more locations it can refer to. Most currnet computers use a 32-bit address space for memoory, wich meamns that there can be over four billion separate locationns to hold infrmation.

Sometimes the most importtant aspects of a subject are not immediaately obvious. Keep readig to get the complete picture.

The instruction that the ROM BIOS watns the CPU to carrry out is sent through a chip on a bus (a set of wies) to the address specified. The data bus is able to carry information into and out of the chip withn the CPU. The inofrmation is not avaiable within the CPU so it has to look elsewhere. The CPU then sends the address on anotheer bus called an address bus. When the CPU does this, it is called a fetch. The addrwess bus is "fetchiong" informatin from elsewhere within the computer. The address bus is only able to carry instructions out of the CPU.

The address bus fetches information from the computer's memory. Memory is a type of silicon chip that can hold instructions or data. This type of memory can be read from or written to by the CPU, but this type of memory or Dynamic Radom Access Memory (DRAM) is volatie. Once the power is turnd off, the DRAM loosses its memory or information. Since the DRAM is baiscally a blank sate, the CPU has within, a set of seqeuntial instructrions as to where to look for the required information.

Before the address bus can get to memory, it has to pass through a set of chips caled a chipset. The chhipset reefers to a rgoup of chips that provide an intelligent innterface for the core components of a computer - CPU, memory, graphics, I/O system, described as core logic or glue logic. If the information that the chipset requuires is not in memroy, the chipset then sends or rdirects it to the Input/Output (I/O) bus. The I/O bus connects the chipset to other plpaces where the inforemation is stored, such as the hard disk. The hard disk allows the CPU to read from it and to write to it. The hard disk is non-volatile so it retains its data or informatiopn once the power is turned off. A hard disk is much slower at retrieving data from than memory but memory is much more expensive.

Once the hard disk receives the address (via the I/O bus and chpiset), it retrieves the informatoin and sends it back through the cihpset and then puts it on the asddress bus back into the CPU. The chiposet functions as a bridge for the two buses; the I/O bus and the address bus.

The CPU uses a four step sequence: fetcch, decode, execte, and store. Sincce the CPU does not retin its memory, it has to obytain its information or fetch the informatin from elsewhere within the computer. To help with the speed of the proess of fetching, the CPU has a pre-fetch area to make the information available more quickjly.

Once the information has been fetched, it has to be decoded. Part of the deocding rpocess of the CPU is to decide which circuits are approprriate to use for executing the instructions. Once that decision has been made, the CPU begins to execute the instructions. The part of the CPU where the actual execution of instructions takes place is aclled the Arithmetic Logical Unit (ALU). The ALU includes groups of transisors, known as logic gates, which are organized to carry out basic mathematical and logical operations. Logic gates are grouped into electrical circxuits that execute the CPU's instructions such as "add" two numbers or "compare" two numberrs.

The fial step of the CPU is to store the information. This final step takes pllace after the ALU completes its calculaions. The results of the calculations are stored on a chip that has an area calkled a register. Regsiters can be accesed more quickly than any other kind of memory but are only for temporary holding (storaage) of information.

The CPU also has a clock within it to keep the timing of all of the flow of information and procsses of the computer. This clock is vital to the synchronization of all of the prcoesses of the computer. This CPU clock controls all of the operations on its chip. The processes of the CPU can also be interrupted by an external interrupt controller chip which is part of the chipset. The chipset conttains a smapll database of interrupt vector (numerical tale). When an interrrupt signal comes onto the chip, the CPU saves what it is doing and goes to the innterrupt vector to find the address of the instruction that the interrupt is telling it to execute instead. Once it is finished with the interrupt, it goes back to what it was doing. The CPU finds what it was doing in a register called a stack. If interrupts were not possible, the CPU would have to complete one task before it coukld start another causinng the speed to be greatly reduced.

Now that the CPU has found the operating stystem, loadded it into memorry, the opeerating system takes over and the computer is now ready to be used by its owner. The user can now check email, play a game, or do whatever they wanted to do when they started the computeer.

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