A bios (Basic Input/Output System) is a small operating system supplied with and usually encoded in the computer hardware. The bios is often little more than is needed to load and run the operating system normally used. Most BIOSs at press time reside in shadow ram which is electronically removed from the computer once the normal operating system is loaded and starts running.
See: Master Boot Record
A disk is a physical storage medium. A disk must be formatted before data on the disk is accessible. A municipal library building is a good model of a disk. The building itslf has a fixed volume and can therefore hold a fixed number of books. The largest number of books can be stored by simply dumping them inside the building, but the result would simply be a big trash pile and the books would not be available for use. In order to use the books, they are placed on bookshelves so they can be accessed. Placing the equivalent of bookshelves on the disk is called formatting
Each bootable partition has firmware that runs in the bios. This firmware historically occupies the 446 bytes before the partition table. A simple master boot record simply copies the operating system from the media into memory and turns computer control over to the operating system.
At power up, cold boot, or warm boot, the bios searches the computer storage media until it finds a master boot record which it then executes it. The search locations and order differ between different bioses. Often the search order is configuratble with firmware encoded in the computer hardware with the bios. The most common search order is floppy, cdrom, network, usb disk, scsi disk, ide disk.
A more complex master boot record, called a boot manager, loads a program into memory that gives the user an opportunity to select which operating system to load.
An operating system is firmware that supports effective computter use. As an allocator, the operating system verifies that only one process at a time controls the cpu , disk, write access to a file, and other unshareable resources. As a toolkit, the operating system provides a set of software pieces for common functions (e.g. reading from a file, writing to the screen). As a virtual machine, the operating system makes the physical computer behave like another well-specified computer, so that software can be written once for the well-specified computer and then run on many physical computers with compatible operating systems. As an allocator, the operating system is like the staff that schedules the use of meeting rooms in the library. As a toolkit, the operating system is like the library staff that reshelves books or the library copier. As a virtual machine, the operating system is like one of the many libraries that endeaver to look like the U.S. Library of Congress with vertical bookshelves, a circular reference desk, and a lobby area with indices. A patron entering any such library finds the layout familiar, and one patron can give usable directions to a patron of a different library.
A disk is a physical portion of a disk. A filesystem is a map between addresses and files accessed on the disk. Most libraries are divided into floors or sections, such as Adult Fiction, Reference, and Juvenile Non-Fiction. Each section usually has its own card catalog and often different sections use different schemes. Adult Fiction is usually indexed by Author Name. Reference is usually indexed by Subject. There are even competing indexing schemes for the same section such as Dewey Decimal or Library of Congress.
Every disk has a partition table stored in a standard location and in a standard format on the disk. The partition table describes where each partition begins and ends on the disk. The partition table also describes what filesystem is used in each partition. The partition table is like the wall map that usually appears at the entry to any library. This wall map tells where each section (e.g. Reference, Adult Fiction, Juvenile Non-fiction) is located and how the books are shelved (e.g. Title, Author, Dewey Decimal)
Before defragmenting, the index (I), active files (A) and deleted files (d) are distributed across the partition.
.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. |I|I|d|A|d|d|d|d|d|d|d|d|A|A|d|d|d|d|d|d|A|A|A|d|d|A| | | | | '-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'
After defragmenting, the index(I), and active files (A) are concentrated. Some deleted files (d) are lost. Some space formerly occupied by active files become lost (l).
.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. |I|I|A|A|A|A|A|A|A|d|d|d|l|l|d|d|d|d|d|d|l|l|l|d|d|l| | | | | '-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'
After splitting, no active data is lost, and a new partition appears that is not yet formatted.
.-.-.-.-.-.-.-.-.-.-. |I|I|A|A|A|A|A|A|A|d| +-+-+-+-+-+-+-+-+-+-+-.-.-.-.-.-.-.-.-.-. |d|d|l|l|d|d|d|d|d|d|l|l|l|d|d|l| | | | | '-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'-'
After repartitioning, the new partition is further split.
.-.-.-.-.-.-.-.-.-.-. |I|I|A|A|A|A|A|A|A|d| +-+-+-+-+-+-+-+-+-+-+ |d|d|l|l|d|d|d|d|d|d| +-+-+-+-+-+-+-+-+-+-+ |l|l|l|d|d|l| | | | | '-'-'-'-'-'-'-'-'-'-'
After formatting, each formatted partition has an empty filesystem. (e.g. dos6 (I, A), ext2 (N, A), vfat (V, A)).
.-.-.-.-.-.-.-.-.-.-. |I|I|A|A|A|A|A|A|A|d| +-+-+-+-+-+-+-+-+-+-+ |N| |N| | | | | | | | +-+-+-+-+-+-+-+-+-+-+ |V|V|V| | | | | | | | '-'-'-'-'-'-'-'-'-'-'
Winmodems are a class of devices including winprinters, winscanners. Winmodems are a subset of the class of devices that achieve low-cost by replacing hardware in their convential equivalents with firmware run by the host. The drawback of these devices is that their dependence on the host usually slows or prohibits other operations simultaneously on the host.
By analogy low-cost headlights for an automobile might consist of a flashlight atop a battery tray that sits in the front passenger seat. To use the headlights, you must start the car, remove the battery from the car, and install the car battery in the flashlight tray. The headlight cost is reduced by the cost of the solenoid, dashboard switch, wiring, and fuses. If you use the headlights, the limitations mean that you can't carry a front passenger, you can't restart the car, you can't use the car radio, and the fuel guage reads empty.
Winmodems are distinct from the slightly larger class of these low-cost devices by the fact that they use proprietary firmware included in the Windows operating system. In the United States, it is illegal to sell firmware to use this proprietary firmware without Microsoft consent. At press time, the price of Microsoft consent is only slightly less than the cost of a convential device.
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Created 1996-2023 by Maxim Chirkov
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