A present computer comprises one or more processors, some main memory, disks, printers, a keyboard, a mouse, a display, network interfaces, and several other input/output devices. All in all, a complex system. If every application programmer had to understand how all
It is difficult to understand exactly what an operating system is other than saying it is the software that runs in kernel mode and even that is not always true. Part of the problem is
The "brain" of the computer is the CPU. It brings instructions from memory and carries out them. The fundamental cycle of every CPU is to bring the first instruction from memory, interpret it to decide its type and operands, execute it, and then bring, decode, and carry out
Operating systems have two major jobs: providing abstractions to user programs and managing the computer's resources. Mostly, the interaction between user programs and the
As we have examined what operating systems look like on the outside (i.e.,the programmer's interface), it is time to take a look inside. In the next sections, we will study six different
One more area where virtual machines are used, but in a somewhat different way, is for running Java programs. When Sun Microsystems invented the Java programming language, it also invented a virtual machine (i.e., a computer architecture)
Different ways have been considered to try to unite the benefits of user-level threads with kernel-level threads. One way is use kernel-level threads and then multiplex user-level threads onto some or all of the kernel threads, as shown in the following figure. When this approach is
We briefly introduced interrupts in "Handheld Computer Operating Systems" but there is more to be said. In a typical personal computer system, the interrupt structure is as illustrated in Figure 1. At the hardware level, interrupts work as follows. When an I/O device has finished
