All aforementioned sources indicate that a warm boot is initiated by pressing Ctrl + Alt + Delete key combination; all except Tulloch (2002) mention that a warm reboot does not perform POST. Jones, Landes, and Tittel (2002) specifies that for a warm reboot to occur, BIOS must be the recipient of the key combination. Microsoft Support article 102228 takes a more technical approach and defines warm boot as the result of invoking INT 19h, a BIOS interrupt call, with the Ctrl + Alt + Delete key combination being only one way of achieving this. According to Grimes (2001), malware may prevent or subvert a warm boot by intercepting the Ctrl + Alt + Delete key combination and prevent it from reaching BIOS.
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The Windows NT family of operating systems also does the same and reserves the key combination for its own use. Soper (2004) asserts that the Windows "Restart" command initiates a warm boot, thus contradicting Jones, Landes, and Tittel (2002), who believe the very same action performs a cold boot. The Linux family of operating systems supports an alternative to warm boot; the Linux kernel has optional support for kexec, a system call which transfers execution to a new kernel and skips hardware or firmware reset. The entire process occurs independently of the system firmware.
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The kernel being executed does not have to be a Linux kernel. Outside the domain of IBM compatible PCs, the types of boot may not be as disambiguous. According to Sue Loh of Windows CE Base Team, Windows CE devices support three types of boots: Warm, cold and clean. A warm boot discards program memory.
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By default the machine ran at 4 MHz, but holding down the 'ESC' key during a cold or warm boot disabled the acceleration so it could run at a standard 1 MHz operation — necessary for older software that depended on timing, especially games. The third major change was the internalization of the power supply into the Apple IIc Plus's case, utilizing a new miniature design from Sony and replacing the previous "brick on a leash" external supply design.
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If Ctrl+Alt+Delete was pressed ("warm boot"), a special flag value stored in nonvolatile BIOS memory ("CMOS") tested by the BIOS allows bypass of the lengthy POST and memory detection. The POST identifies, and initializes system devices such as the CPU, RAM, interrupt controllers, DMA controllers, chipset, video display card, keyboard, hard disk drive, optical disc drive and other hardware. Early IBM PCs had a routine in the POST that would download a program into RAM through the keyboard port and run it. This feature was intended for factory test or diagnostic purposes.
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Jones, Landes, and Tittel (2002) contradicts this assertion and states that a reset button may commence either a cold or warm reboot, depending on the system. Microsoft Support article 102228 states that although the reset button is designed to perform a cold reboot, it may not disconnect the power to the motherboard – a state that does not correspond to the cold boot definition given above. According to Jones, Landes, and Tittel (2002), both the operating system and third-party software can initiate a cold boot; the restart command in Windows 9x initiates a cold reboot, unless Shift key is held. Finding a definition for warm boot, however, is more of a challenge.
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