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.
43. What is page frame?
An area in the main memory that can hold one page is called a page frame.
44. What is a page table base register?
The starting address of the page table is kept in a page table base register
45. What is Transaction Look aside Buffer?
A copy of the page table entries that correspond to the most recently used accessed pages are stored in a small cache called the Translation Look aside Buffer.
46. What is page fault?
When a program generates an access request to a page that is not in the main memory a page fault is said to have occurred.
47. What is meant by System space?
System space is a virtual address space in which the operating system routines are assembled.
48. What are the two states of processor?
The two states of the processor are
• Supervisor state
• User state
The processor is placed in the supervisor state when operating system routines are being executed and in the user state to execute user programs.
49. Define Winchester technology?
Cache memory Virtual memory
1. Cache memory bridges the speed gap between the processor And the main memory.
2. It is implemented in hardware Virtual memory bridges the size and
Sped gaps between the main memory and the secondary storage
It is implemented by software techniques In modern disk units, the disks and the read/write heads are placed in a sealed, air- filtered enclosure. This approach is known as Winchester technology.
50. Give the advantages of Winchester technology?
• Operate closer to the magnetized track surfaces
• Larger capacity
• Data integrity is greater
51. What are the parts of the disk system?
• Disk
• Disk drive
• Disk controller
Disk: Assembly of disk platters.
Disk drive: Electromechanical mechanism that spins the disk and moves the read/write heads.
Disk controller: Electronic circuitry that controls the operation of the system.
52. What do you mean by a logical cylinder in a disk?
Each surface in a disk is divided into concentric tracks, and each track is divided into sectors. The set of corresponding tracks on all surfaces of a stack of disk forms a logical cylinder.
53. What is meant by intersector gap?
Each surface in a disk is divided into concentric tracks, and each track is divided into sectors. In order to distinguish between two consecutive sectors a separation is provided which is known as intersector gap.
54. What is meant by seek time?
The time required to move the read/write head to the proper track is called as seek time. This depends on the initial position of the head relative to the track specified in the address.
55. Define latency time?
Latency time is also called as rotational delay. This is the amount of time that elapses after the head is positioned over the correct track until the starting position of the addressed sector passes under the read/write head.
56. What is a data buffer?
Data buffer in the disk unit is a semiconductor memory, capable of storing a few MB of data. The data buffer can be also used to provide a caching mechanism for the disk.
57. What are the uses of a disk controller?
Disk controller provides an interface between the disk drive and the bus that connects it to the rest of the system. It is also used to control multiple drives.
58. Give the functions of the disk controller?
The functions of the disk controller are, o Seek o Read o Write o error checking
59. What is meant by booting?
The process of loading the OS into the main memory as soon as the power is turned on is called as booting.
60. What are the secondary storage devices? Give their advantages over secondary storage devices?
Optical disks, magnetic disks and magnetic tapes are the secondary storage devices. Their advantages over semi conductor memories are, o Inexpensive o Larger storage capability
61. What is floppy disk?
Floppy disks are smaller, simpler and cheaper disk units that consist of a flexible, removable plastic diskette coated with magnetic material.
62. What are the advantages and disadvantages of floppy disk?
Advantages: o Smaller & simpler. o Low cost. o Shipping convenience.
Disadvantages: o Longer access times. o Smaller storage capacities.
o Higher failure rates than hard disks.
63. Define data striping.
A single large file is stored in several separate disk units by breaking the file up into a number of smaller pieces and storing these pieces on different disks. This is called as data striping.
64. What is RAID?
RAID stands for Redundant Array of Inexpensive Disks. It is a storage system based on multiple disks (Five). It is also referred as Redundant Array of Independent Disks.
65. Give the features of RAID Disks? o Provides excellent performance o Large storage o Reliable
66. Enumerate the features of SCSI disks? o More expensive. o Exhibit better performance. o Concurrent accesses can be made to multiple disk drives.
67. Outline the features of ATA/ EIDE disks?
ATA/EIDE stands for advanced technology attachment and Enhanced integrated drive electronics.
Features: o Low price. o Separate controller is needed for each drive.
68. Explain the terms pits and lands?
Pits:
In a CD the bottom layer is poly carbonate plastic, which functions as a clear glass base. The surface of this plastic is programmed to store data by indenting it with pits.
Lands:
The unintended parts are called lands.
69. Briefly explain ECC?
ECC stands for Error Correcting Codes. Data bits are stored serially on each track and is preceded by a sector header containing identification information and succeeded by a additional bits that constitute an error correcting code.ECC bits are used to detect and correct errors that may have occurred in writing or reading data bytes.
70. Define Cartridge tape system?
Tape systems have been developed for back up of on-line disk storage. One such system uses an 8 mm video format tape housed in a cassette. These tapes are called cartridge tapes.
71. What are the operations of control commands in a magnetic tape drive controller?
Control commands include the following operations, o Rewind and unload tape o Rewind tape o Erase tape o Write tape mark o Forward space one record o Backspace one record o Forward space one file o Backspace one file
72. What are the advantages of CD ROMs over magnetic disks?
Advantages: o Large storage capacity o Fast access times o Small physical size o Low cost o Easily transportable and removable
73.What is the purpose of the three different laser powers in CD-RW drive? o Highest power: Used to record the pits o Middle power (Erase power): Used to put the alloy into its crystalline state. o Lowest power: Used to read the stored information.