COMPUTER ORGANISATION AND ARCHITECTURE UNIT IV TWO MARKS 1. What is meant by memory access time? Memory access time is defined as the time that elapses between the initiation of an operation and the completion of that operation. It is a useful measure of the speed of memory units. E.g. the time between the read and the MFC signals. 2. Define memory cycle time. The minimum time delay required between the initiation of two successive operations is known as memory cycle time. The cycle time is usually slightly longer than the access time. E.g. the time between two successive Read operations. 3. What is a RAM? A memory unit is called random-access memory (RAM) if any location can be accessed for a Read or Write operation in some fixed amount of time that is independent of the location’s address. 4. Define cache memory. Mention its use. The small and fast memory that is inserted between the larger, slower main memory and the processor is called a cache memory. It holds the currently active segments of a program and their data. Use: It is used to increase the execution speed. 5. What is meant by virtual memory? Why it is used? A virtual memory is a memory in which data are stored in physical memory locations that have addresses different from those specified by the program. Virtual memory is used to increase the apparent size of the physical memory. 6. What is meant by virtual or logical address? In virtual memory, the memory control circuitry translates the address specified by the program into an address that can be used to access the physical memory. In such a case, the binary address generated by the processor is referred to as a virtual or logical address. 7. What is a MMU? Memory management unit (MMU) is a special memory control circuit that implements the mapping function. This hardware unit translates virtual addresses into physical addresses. 8. What are static memories? Give example. Memories that consist of circuits capable of retaining their state as long as power is applied are known as static memories.e.g. Static RAM (SRAM) 9. What is meant by asynchronous DRAMS? Cells that don’t retain their state infinitely are called DRAMS (Dynamic RAMS) and if the processor takes into account the delay in the response of the memory then such memories are called asynchronous DRAMS. 10. What are SDRAMS? DRAMS whose operation is directly synchronized with a clock signal are known as Synchronous DRAMS (SDRAMS). 11. What are the two parameters of performance of a computer system? Define them. The two parameters of performance are Latency Bandwidth The term memory latency is used to refer to the amount of time it takes to transfer a word of data to or from the memory. The term bandwidth is used to refer to the number of bits or bytes that can be transferred in one second. 12. What are DDR SDRAMS? Mention their use. Double Data Rate SDRAM is a memory device that accesses the cell array similar to SDRAM but transfers data on both the edges of the clock. Since they transfer data on both edges of the clock their bandwidth is doubled for long burst transfers. Use: They are used in applications where block transfers are prevalent. 13. Define Fast Page Mode. Mention its use. Fast page mode is a scheme that is used to transfer data bytes in sequential order by applying a consecutive sequence of column addresses instead of random addresses. This allows block data transfer at a much faster rate. Uses: It is used in Graphics terminals General purpose computers for block transfer between main memory and cache memory 14. What is a memory controller circuit? A typical processor issues all bits of an address at the same time. The required multiplexing of address bits is performed by a memory controller circuit . 15. What is the feature of Rambus memory? STATIC RAM DYNAMIC RAM Static RAMs are fast Dynamic RAMs are slower They are expensive They are much less expensive Their cells require several Their size is small since they have Transistors. So their size is large simpler basic cells Circuit is complex Circuit is simple. 17. What is meant by differentially signaling? Using signals that have voltages that have 0.3V swings above and below the reference voltage (Vref ) is called as differential signaling. 18. What is meant by rambus channel? Rambus provides a complete specification for the design of special circuit interfaces to deal with the differential signals, called the rambus channel. 19. Define RDRAM. Chips that use cell array based on standard DRAM technology in which the circuitry needed to interface to the rambus are included are known as RDRAM(Rambus DRAM). 20. What are packets? Give its types. Communication between the processor (master) and RDRAM modules (slaves) is carried out by means of packets transmitted on the data lines. There are three types of packets. They are Request Acknowledge Data 21. What is a direct RDRAM? A two channel RDRAM is known as a direct RDRAM.It has 18 data lines intended to transfer two bytes of data at a time. There are no separate address lines. 22. What is ROM? ROM (Read only Memory) is a non-volatile memory whose normal operation involves only reading of data. 23. What is PROM? The ROM that allows data to be loaded by the user is called Programmable ROM.Programmability is achieved by inserting a fuse at the point P in the ROM cell. 24. Mention the advantages of PROM over ROM? Provides Flexibility Less expensive Faster 25. What is an EPROM? The ROM chip that allows a stored data to be erased and new data to be loaded is called as an Erasable re Programmable ROM. 26. How erasure is done in EPROM? Erasure requires dissipating the charges trapped in the transistors of memory cells .This can be done by exposing the chip to Ultra Violet light. 27. What is an EEPROM? Mention its advantage &Disadvantage. ? Erasable PROMs that can be both programmed and erased electrically. Such chips are called Electrically Erasable PROM. Advantages: Need not be physically removed for erase the cell contents. Cell contents can be selectively erased. Disadvantage: Different voltages are needed for erasing, reading, and writing the data. 28. Give the difference between flash drives and hard drives. Hard Drive Flash Drive 1.They can store many Gigabytes The capacity of flash drives is less than oneGB. 2.Less cost per bit Higher cost per bit 29. Enumerate the advantages of flash drives. Advantages: Shorter seek and access timeFaster response Lower power consumption Insensitive to vibration They have no movable parts which provide some advantages. 30. Give the applications of flash memory. Applications: Hand held computers and cell phones: Flash memory holds the software needed to operate Digital cameras: Flash memory holds the picture image data. MP3 players: Flash memory stores the data that represent sound. 31. What is locality of Reference? Many instructions in the localized areas of the program are executed repeatedly during some period, and the remainder of the program is accessed relatively infrequently. This is referred to as locality of reference. 32. What is a replacement algorithm? When the cache is full and the memory word is not in the cache is referenced the cache control hardware must decide which block should be removed to create space for the new word block that contains the referenced word. The collection of rules for making this decision constitutes the replacement algorithm. 33. What is a hit? When the processor issues a read or write request, the cache control circuitry determines whether the requested word exists in the cache memory. If it does then the Read or Write operation is performed on the appropriate cache location. Then a read or Write hit is said to have occurred. 34. What is a miss? When the processor issues a read or write request, the cache control circuitry determines whether the requested word exists in the cache memory. If the word is not in the cache memory, then a read or Write miss is said to have occurred. 35. What is mapping? The transformation of data from main memory to cache memory is referred to as a Mapping process. 36. What are the three types of mapping? The three types of mapping are Associative mapping Direct mapping Set associative mapping 37. What is LRU? When a new block is to be brought into the cache and all the positions in the cache are full, the cache controller has to overwrite on the block that has gone the longest time without being referenced. This block is called the least recently used (LRU) block. 38. What are virtual memory techniques? The techniques that automatically move program and data blocks from secondary storage devices into the physical memory when they are required for execution are called virtual memory techniques. 39. What are blocks? The physical memory is broken down in to groups of equal size called blocks. 40. What is a page? Page is a fixed length unit which consists of block of words that occupy contiguous locations in the main memory. Page is the basic unit of information that is moved between the main memory and the disk 41. Give the differences between the cache memory and the virtual memory. 42. What is a page table? Information about the main memory location of each page is kept in a page table. This information includes the main memory address where the page is stored and the current status of the page.