26-04-2014, 03:03 PM
Q Real time clock
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A A real-time clock (RTC) is a computer clock (most often in the form of an integrated circuit) that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time.
Although keeping time can be done without an RTC,[1] using one has benefits:
Low power consumption [2] (important when running from alternate power)
Frees the main system for time-critical tasks
Sometimes more accurate than other methods
Most RTCs use a crystal oscillator,[6][7] but some use the power line frequency.[8] In many cases the oscillator's frequency is 32.768 kHz.[6] This is the same frequency used in quartz clocks and watches, and for the same reasons, namely that the frequency is exactly 215 cycles per second, which is a convenient rate to use with simple binary counter circuits.
Q Memory Management
A Memory management is the act of managing computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed. This is critical to the computer system.
Several methods have been devised that increase the effectiveness of memory management. Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the effectively available amount of RAM using paging or swapping to secondary storage
Q Real- Time operating system?
A A real-time operating system (RTOS) is an operating system (OS) intended to serve real-time application requests. It must be able to process data as it comes in, typically without buffering delays. Processing time requirements (including any OS delay) are measured in tenths of seconds or shorter.
A key characteristic of an RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application's task; the variability is jitter.[
An RTOS that can usually or generally meet a deadline is a soft real-time OS, but if it can meet a deadline deterministically it is a hard real-time OS. [2]
Q Program status word?
A The Program status word[1][2] (PSW) is an IBM System/360 architecture and successors control register which performs the function of a Status register and Program counter in other architectures, and more.
Although certain fields within the PSW may be tested or set by using non-privileged instructions, testing or setting the remaining fields may only be accomplished by using privileged instructions.
Contained within the PSW are certainly the zero (non-zero) and carry (borrow) flags and similar flags of other architectures' status registers, in this case encoded as a condition code with values from 0 to 15, representing the arithmetic sum of the four condition code bit values, 23 + 22 + 21 + 20.