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Leave this field empty. Trending Today. Load more. Get New Updates Email Alerts Enter your email address to subscribe this blog and receive notifications of new posts by email. Join With us. Today Updates. August 8. July June Firmware consists of persistently stored microcode instructions that perform the tasks specified by machine language. Firmware specifies software instructions but is part of the hardware. Some items can have more than one answer.
Has overall computer performance doubled at the same rate? Why or why not? Ans: Although processor speeds have increased at an astonishing rate, slower development of memory technologies prevents overall computer performance from increasing at the same rate. Register memory, L1 cache, L2 cache, main memory, secondary storage, tertiary storWhy do systems contain several data stores of different size and speed? Ans: The faster a type of memory is, the more expensive it is.
It would also be nice to include a lot of memory in the system cheaply, but using only the slowest type of memory tertiary storage would make a system much too slow. Therefore, systems include many different types of memory so that the data accessed most-often is stored in the faster type of memory, increasing performance while still being able to store large quantities of data using the slower types of memory.
Also, faster memory is volatile, so a system must include some type of permanent storage so that all data is not lost. What is the motivation behind caching? Caching is a mechanism that speeds memory access by keeping duplicate copies of data that the system thinks will be accessed in the future in fast memory.
Caches are used so that systems can store a large volume of data, but still enjoy low memory access times. However, it would greatly benefit servers that need to be able to recover from power outages quickly, because the system could return to the state it was in before the outage. Why is it important to support legacy architectures? It allows software that has been written for previous architectures to be reused. Ans: The principle of least privilege states that programs should only have the level of privilege they need to carry out their functions, and no more.
This prevents accidental or malicious corruption of the system. Users execute in the user mode; the operating system executes in the kernel mode. Bounds registers may be used to specify a continuous range of addresses a program may access. Out-of-bounds references are not allowed. Virtual memory provides memory protection as well, because processes are unaware of the physical addresses to which the virtual addresses correspond.
Therefore, a process may not access a physical address without the permission of the operating system. On double-buffered input, for example, while a processor consumes one set of data in one buffer, the channel reads the next set of data into the other buffer so that the data will hopefully be ready for the processor. Explain in detail how a triple-buffering scheme might operate. Ans: Consider a triple-buffered input scheme. First the channel reads data into buffer1.
As the processor processes the data in buffer1, the channel proceeds to read data into buffer2 so that the data will hopefully be ready for the processor when the processor needs it.
When the channel finishes reading data into buffer2, it begins reading data into buffer3, attempting to stay ahead of the processor. Eventually, the channel will want to deposit more data, so it might need to wait until the processor is finished processing the data in buffer1. Occasionally, the processor might need to wait for the channel to deposit more data for it to work with.
Thus, the depositing of data and the reading of the data proceed in circular fashion using buffer1, then buffer2, then buffer3. This cycle repeats until all the data has been processed.
In what circumstances would triple buffering be effective? Ans: Buffers are usually relatively large areas of storage, so before installing a triple-buffering scheme, we would like to know that it is worthwhile.
Clearly, if the processor is much faster than the channel in the triple-buffered input scheme, then the channel may never be able to get far enough ahead of the processor to take advantage of the third buffer.
Ideally, multiple-buffering schemes are used to pick up the occasional slack when one unit gets slightly ahead of the other. This can result in significant performance improvement. The two techniques are interrupts and polling. With polling, the processor repeatedly checks to see if it must service the channel. If not, then the processor tests the next channel. With polling, the processor is essentially always in control, but it may waste time discovering that devices do not need its attention.
The advantage is that no time is wasted on devices that do not need attention. Although both processors and channels need to have access to a memory module, only one may control the bus at a time.
Early systems transferred data a character or word at a time to memory and interrupted the processor after each transfer.
These interrupts reduced the time during which a processor could execute program instructions. With DMA, the processor is interrupted only after a block of data has been transferred.
One of the most common types of spooling is print spooling. Instead of a program directing its output to a relatively slow mechanical printing device, output is placed in a disk file spool file. The program can run at the speed of the disk and therefore finish more quickly. When the printer becomes available, it reads the data from the spool file.
Because the disk is much faster than the printer, the spooling program can drive the printer at top speed while the original user program proceeds with new activities in parallel with the spooling this is one of the most common forms of multitasking, especially on personal computers.
How, do you suppose, does an input spooling system designed to read punched cards from a card reader operate? First the deck of punched cards is spooled to a disk file. Then, as the program executes, it reads the card images from the disk much faster than it could from the card reader. The presumption is that the input spooling is completed before the program executes, so that the card images will be available as the program needs them.
In the interim, while the cards are being spooled to disk, the program is performing other tasks. Although punched cards are not used today, the spooling principle illustrated here is still valid. Indicate which of these categories is best defined by each of the following. Millions discover their favorite reads on issuu every month.
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