Operating systems cannot be put into nice, neat pigeonholes like hardware. By nature software is vague and amorphous. Still, it is more-or-less possible to distinguish two kinds of operating systems for multiple CPU systems: loosely coupled and tightly coupled. As we shall see, loosely and tightly-coupled software is roughly analogous to loosely and tightly-coupled hardware.. 1.4.3. Multiprocessor Timesharing Systems. CallInputOutputRegisterName, version, handle, unique idDeregisterName, version, unique idLookupName, versionHandle, unique id. In general, eliminating copying is easier on the sending side than on the receiving side. With cooperative hardware, a reusable packet header inside the kernel and a data buffer in user space can be put out onto the network with no internal copying on the sending side. When it comes in at the receiver, however, even a very intelligent network chip will not know which server it should be given to, so the best the hardware can do is dump it into a kernel buffer and let the kernel figure out what to do with it.. With one small addition, this algorithm meets our requirements for global time. The addition is that between every two events, the clock must tick at least once. If a process sends or receives two messages in quick succession, it must advance its clock by (at least) one tick in between them.. Despite the fact that the CPU may have to deal with multiple event streams, it is not acceptable for it to say: It is true that I missed eventB, but it is not my fault— I was still working onA whenB happened. While it is not hard to manage two or three input streams with priority interrupts, as applications get larger and more complex (e.g., automated factory assembly lines with thousands of robots), it will become more and more difficult for one machine to meet all the deadlines and other real-time constraints.. An alternative design that does not suffer from this problem is thetime-triggered real-time system.In this kind of system, a clock interrupt occurs every AT milliseconds. At each clock tick (selected) sensors are sampled and (certain) actuators are driven. No interrupts occur other than clock ticks.. 17. Using the data of Fig. 4-20, what is the longest UNIX pipeline that can be co-scheduled?. For example, if there are five servers and a client determines that three of them have version 8, it is impossible that the other two have version 9. After all, any successful update from version 8 to version 9 requires getting three servers to agree to it, not just two.. 6.4.6. Finding the Copies. Like most operating systems, Amoeba supports the concept of a process. In addition, Amoeba also supports multiple threads of control within a single address space. A process with one thread is essentially the same as a process in UNIX. Such a process has a single address space, a set of registers, a program counter, and a stack.. Thepriority andassign calls give the programmer control over how and where its threads run on multiprocessor systems. CPU scheduling is done using priorities, so the programmer has fine-grain control over which threads are most important and which are least important. Theassign call makes it possible to control which thread runs on which CPU or group of CPUs.. Open files are not the only UNIX concepts that are mapped onto Chorus resources. Open directories (including the working directory and root directory), open devices, pipes, and in-use segments are all represented internally as capabilities for the corresponding Chorus resources. Operations on all of these are done by the UNIX subsystem by passing the capability to the appropriate server. To remain binary compatible with UNIX, the user process must never see the capabilities.. In UNIX (and all uniprocessor operating systems, for that matter), when one process writes on a file, and then signals a second process to read the file, the value readmust be the value just written. Getting any other value violates the semantics of the file system.. 2. DCE threads can be in one of four states, as described in the text. In two if these states, ready and waiting, the thread is not running. What is the difference between these states?.