As the BIOS program can only be managed to FFFFF, high memory (A0000 or higher memory) is used to map BIOS, video card memory and other peripherals. The conventional memory of the PC is only 640K. However, 1 / 13s is not fast enough to switch through many processes but using the BIOS function can speed up the SCHED 1 / 100s once. Multitasking operating systems later used this principle to make SCHED. In this application I write a banner run program in the DOS screen, or one or more ping pong games that hit the sides of the screen while running DOS. If you write a hook int 1Ch subroutine, you will have the feeling that it runs parallel to the main program (actually 1 / 13s it ran once). The IRQ timer will then call the 1Ch interrupt. Then the CPU will stop the command being executed by switching the interrupt handler. The default is 1/13 second once the transmitter sends an IRQ signal to the CPU. IRQ Timer is a hard interrupt, ie the signal sent by the pulse to the CPU.
Interrupt 1Ch is actually IRQ Timer (6 or 8 forget it) call. The old MSDOS operating system was actually a single operating system, but you could still interrupt 1Ch (hook interrupt) to simulate multitasking. This is extremely fast so you have no feeling. For example, if you just hit Winword and play Winamp, then SCHED will run Winword 5.10 command is finished, go to Winamp 5.10 command and switch back and forth. How do they do it? By passing the executable back and forth between programs so fast that we have the feeling that programs are running at the same time. allow multiple programs to run at the same time. However, multi-tasking systems such as Windows, Linux etc. The Linux kernel consists of five major sub-systems:Īs you know, the PC is basically a single-processor system that only has one executable at a time.
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