<P> Starting: - The first commercial licensing of CP / M took place in 1975 with contracts between Digital Systems and Omron of America for use in their intelligent terminal, and with Lawrence Livermore Laboratories where CP / M was used to monitor programs in the Octopus network . Little attention was paid to CP / M for about a year . In my spare time, I worked to improve overall facilities...By this time, CP / M had been adapted for four different controllers...In 1976, Glenn Ewing approached me with a problem: Imsai, Incorporated, for whom Glenn consulted, had shipped a large number of disk subsystems with a promise that an operating system would follow . I was somewhat reluctant to adapt CP / M to yet another controller, and thus the notion of a separated Basic I / O System (BIOS) evolved . In principle, the hardware dependent portions of CP / M were concentrated in the BIOS, thus allowing Glenn, or anyone else, to adapt CP / M to the Imsai equipment . Imsai was subsequently licensed to distribute CP / M version 1.3 which eventually evolved into an operating system called IMDOS . </P> <Tr> <Td_colspan="3">--Gary Kildall </Td> </Tr> <P> The BIOS of the original IBM PC XT had no interactive user interface . Error codes or messages were displayed on the screen, or coded series of sounds were generated to signal errors when the power - on self - test (POST) had not proceeded to the point of successfully initializing a video display adapter . Options on the IBM PC and XT were set by switches and jumpers on the main board and on peripheral cards . Starting around the mid-1990s, it became typical for the BIOS ROM to include a "BIOS configuration utility" (BCU) or "BIOS setup utility", accessed at system power - up by a particular key sequence . This program allowed the user to set system configuration options, of the type formerly set using DIP switches, through an interactive menu system controlled through the keyboard . In the interim period, IBM - compatible PCs‍--‌including the IBM AT ‍--‌held configuration settings in battery - backed RAM and used a bootable configuration program on disk, not in the ROM, to set the configuration options contained in this memory . The disk was supplied with the computer, and if it was lost the system settings could not be changed . The same applied in general to computers with an EISA bus, for which the configuration program was called an EISA Configuration Utility (ECU). </P> <P> A modern Wintel - compatible computer provides a setup routine essentially unchanged in nature from the ROM - resident BIOS setup utilities of the late 1990s; the user can configure hardware options using the keyboard and video display . Also, when errors occur at boot time, a modern BIOS usually displays user - friendly error messages, often presented as pop - up boxes in a TUI style, and offers to enter the BIOS setup utility or to ignore the error and proceed if possible . Instead of battery - backed RAM, the modern Wintel machine may store the BIOS configuration settings in flash ROM, perhaps the same flash ROM that holds the BIOS itself . </P>

Where is bios stored on early personal computers what is the disadvantage
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