UNIT I
1. What are the types of computer?
Personal computer, notebook computer, workstations, enterprise or mainframes.
2. What are the functional units of a computer?
Input unit, memory unit, arithmetic and logic unit, output unit and control unit.
3. What is a program?
A list of instructions that performs a task is called a program. Usually the program is stored in memory.
4. What is object program?
Compiling a high-level language source program in to a list of machine instructions constituting a machine language program is called an object program. It is the assembled machine language program.
5. What do you mean by bits?
Each number, character, or instruction is encoded as a string of binary digits called as bits, each having one of two possible values, 0 or 1.
6. Define RAM.
Memory in which any location can be reached in a short fixed time after specifying its address is called random-access memory (RAM).
7. Define word length.
The number of bits in each word is often referred to as the word length of the computer. Typical word lengths range from 16 to 64 bits.
8. Define memory access time?
The time required to access one word is called as memory access time. This time is fixed and independent of the location of the word being accessed. It typically ranges from a few nanoseconds (ns) to about 100 ns for modern RAM units.
9. What is memory hierarchy?
The memory of a computer is normally implemented as a memory hierarchy of three or four levels of semiconductor RAM units with different speeds and sizes. The small, fast RAM units are called caches. The large and slowest unit is referred to as main memory.
10. What is primary storage and secondary storage?
Primary memory is a fast memory that operates at electronic speeds. It is expensive. Secondary memory is used when large amounts of data and many programs have to be stored, particularly for information that is accessed infrequently.
11. What are registers?
Registers are high speed storage elements. Each register can store one word of data. Access time to registers is faster than access time to the fastest cache memory.
12. What are timing signals?
Timing signals are generated by the control circuits. These are signals that determine when a given action should take place. Data transfers between the processor and memory are also controlled by the control unit through the timing signals.
13. Explain briefly the operation of Add LOCA, R0.
This instruction adds the operand at memory location LOCA to the operand in a register in the processor, R0, and places the sum in to register R0. The original contents of location LOCA are preserved, whereas those of R0 are overwritten.
14. What is instruction register?
The instruction register (IR) holds the instruction that is currently being executed. Its output is available to the control circuits which generate the timing signals that control the various processing elements involved in executing the instruction.
15. What is program counter?
The program counter (PC) keeps track of the execution of a program. It contains the memory address of the next instruction to be fetched and executed.
16. What is MAR and MDR?
The memory address register (MAR) holds the address of the location to be accessed. The memory data register (MDR) contains the data to be written into or read out of the addressed location.
17. What is an interrupt?
An interrupt is a request from an I/O device for service by the processor. The processor provides the requested service by executing an appropriate interrupt-service routine.
18. Define bus.
A group of lines that serves as a connecting path for several devices is called a bus. In addition to the lines that carry data, the bus must have lines for address and control purposes.
19. What is a compiler?
It is a system software program that translates the high-level language program into a suitable machine language program.
20. What is a text editor?
It is a system program used for entering and editing application programs.
21. What is a file?
A file is simply a sequence of alphanumeric characters or binary data that is stored in memory or in secondary storage. A file can be referred by a name chosen by the user.
22. Define OS.
Operating system (OS) is a large program, or a collection of routines, that is used to control the sharing of and interaction among various computer units as they execute application programs.
23. What is multiprogramming or multitasking?
The operating system manages the concurrent execution of several application programs to make the best possible use of computer resources. This pattern of concurrent execution is called multiprogramming or multitasking.
24. What is elapsed time?
It is a measure of performance of the entire computer system. It is affected by the speed of the processor, the disk and the printer.
25. What is processor time?
The sum of the periods during which the processor is active is called the processor time.
26. What are clock and clock cycles?
The timing signals that control the processor circuits are called as clocks. The clock defines regular time intervals called clock cycles.
27. Give the basic performance equation.
T = (N * S)/R
Where, T – performance parameter
N – actual number of instruction executions
S – average number of basic steps needed to execute one machine instruction
R – clock rate in cycles per second.
28. What is pipelining?
The technique of overlapping the execution of successive instruction for substantial improvement in performance is called pipelining.
29. What is superscalar execution?
In this type of execution, multiple functional units are used to create parallel paths through which different instructions can be executed in parallel. so it is possible to start the execution of several instructions in every clock cycle. This mode of operation is called superscalar execution.
30. What is RISC and CISC?
The processors with simple instructions are called as Reduced Instruction Set Computers(RISC). The processors with more complex instructions are called as Complex Instruction Set Computers (CISC).
31. Define SPEC rating.
Running time on the reference computer
SPEC rating = Running time on the computer under test
32. Define byte addressable memory.
Byte locations have addresses 0,1,2….Thus if the word length of the machine is 32 bits, successive words are located at addresses 0,4,8….with each word consisting of 4 bytes. This is called byte addressable memory.
33. What is big-endian and little-endian?
The name big-endian is used when lower byte addresses are used for the more significant bytes (the leftmost bytes) of the word. The name little-endian is used when lower byte addresses are used for the less significant bytes (the rightmost bytes) of the word.
34. What is aligned address?
Words are said to be aligned in memory if they begin at a byte address that is a multiple of the number of bytes in a word.
35. Explain briefly the operation of ‘load’.
The load operation transfers a copy of the contents of a specific memory location to the processor. The memory contents remain unchanged. To start a load operation, the processor sends the address of the
desired location to the memory and requests that its contents be read. The memory reads the data stored at that address and sends them to the processor.
36. Explain briefly the operation of ‘store’.
The store operation transfers an item of information from the processor to a specific memory location, destroying the former contents of that location. The processor sends the address of the desired location to the memory, together with the data to be written into that memory location.
37. What is register transfer notation?
R3 <- [R1] + [R2]
This type of notation is known as register transfer instruction (RTN). The right-hand side of an RTN expression always denotes a value, and the left-hand side is the name of a location where the value is to be placed, overwriting the old contents of that location.
38. What is a one address instruction?
The instruction that contains the memory address of only one operand is called one address instruction.
Eg. Load A, Store A.
39. What is a two address instruction?
The instruction that contains the memory address of two operands is called two byte address instruction.
Eg. Add A,B , Move B,C.
40. What is a three address instruction?
The instruction that contains the memory address of three operands is called three byte address instruction.
Eg. Add A,B,C.
41. What is a zero address instruction?
Instructions in which the locations of all operands are defined implicitly is called zero address instruction. Such instructions are found in machines that store operands in a structure called pushdown stack.
42. What is straight line sequencing?
To begin executing a program, the address of its first instruction must be placed into PC. Then the processor control circuits use the information in the PC to fetch and execute instructions, one at a time, in the order of increasing addresses. This is called straight line sequencing.
43. Define conditional branch.
A conditional branch instruction causes a branch only if a specified condition is satisfied. If the condition is not satisfied, the PC is incremented in the normal way and next instruction in the sequential address is
fetched and executed.
44. Define conditional code flags.
The processor keeps track of information about the results of various operations for use by subsequent conditional branch instructions. This is done by recording the required information in individual bits called as conditional code flags.
45. Define conditional code register (OR) status register.
The conditional code flags are usually grouped together in a special processor register called conditional code registers or status registers.
46. What are the four commonly used flags?
N (negative) – set to 1 if the result is negative; otherwise, cleared to 0
Z (zero)- set to 1 if the result is 0; otherwise, cleared to 0
V (overflow) – set to 1 if arithmetic overflow occurs; otherwise, cleared to 0
C (carry)- set to 1 if the carry-out results from the operation; otherwise, cleared to 0
47. What is addressing modes?
The different ways in which the location of a operand is specified in an instruction is referred to as addressing modes.
48. What are the various addressing modes?
Register mode, absolute mode, immediate mode, indirect mode, index mode, relative mode, auto increment mode, auto decrement mode.
49. Define register mode addressing.
In register mode addressing the operand is the contents of a process register. The name of the register is given in the instruction.
50. Define absolute mode addressing.
In absolute mode addressing the operand is in a memory location. The address of this location is given explicitly in the instruction. This is also called direct mode addressing.
51. Define immediate mode addressing.
In immediate mode addressing, the operand is given explicitly in the instruction.
Eg. Move #200,R0.
52. Define indirect mode addressing.
In indirect mode addressing the effective address of the operands is the content of a register or memory location whose address appears in the instruction.
Eg: Add (R2),R0.
53. What is a pointer?
The register or memory location that contains the address of an operand is called a pointer.
Eg: A= *B. Here B is a pointer variable.
54. Define index mode addressing.
In index mode addressing, the effective address of the operand is generated by adding a constant value to the register.
EA= X + [Ri].
55. Define relative mode addressing.
In relative mode addressing the effective address is determined by the index mode using the program counter in the place of the general purpose register Ri.
56. Define Auto increment mode.
In this mode the effective address of the operand is the contents of a register specified in the instruction. After accessing the operand, the contents of this register are automatically incremented to point to the next item in a list. It can be written as (Ri)+.
57. Define Auto decrement mode.
In this mode the contents of a register specified in the instruction are first automatically decremented and then used as the effective address of the operand. . It can be written as -(Ri).
58. What are mnemonics?
When writing programs for a specific computer, words such as Move, Add, Increment and Branch are replaced by acronyms such as MOV, ADD, INC and BR. This is called mnemonics.
59. What is an assembler?
Programs written in assembly language can be automatically translated in to a sequence of machine instructions by a program called an assembler.
60. What is a source program?
The user program in its original alphanumeric text format is called a source program.
61. What are assembler directives?
Consider the example SUM EQU 200. This statement does not denote an instruction that will be executed when the object program is run. This will not even appear in the object program. It simply informs the assembler that the name SUM should be replaced by the value 200 wherever it appears in
the program. Such statements are called assembler directives.
62. What is symbol table?
As the assembler scans through a source program, it keeps track of all names and the numeric values that correspond to them in a table called symbol table. Thus, when a name appears a second time, it is replaced with its value from the table.
63. What is a two pass assembler?
During the first pass of the assembler it creates a complete symbol table. At the end of this pass, all the names will be assigned numeric values. The assembler then goes through the source program second time and substitutes values for all names from the symbol table. Such an assembler is called a two-pass assembler.
64. What is a loader?
The assembler stores the object program on a magnetic disk. The object program must be loaded into the memory of the computer before it is executed. For this to happen, another utility program must already be loaded in the memory. This program is called a loader.
65. What is the use of debugger program?
The debugger program enables the user to stop execution of the object program at some points of interest and to examine the contents of various processor registers and memory locations.
66. What are device interface?
The buffer registers DATAIN and DATAOUT and the status flags SIN and SOUT are part of circuitry and they are commonly known as device interface.
67. Define memory mapped I/O.
Many computers use an arrangement called memory mapped I/O in which some memory address values are used to refer to peripheral device buffer registers, such as DATAIN and DATAOUT. This no special instructions are needed to access the contents of these registers.
68. What is a stack?
A stack is a list of data elements, usually words or bytes , with the accessing restriction that elements can be added or removed at one end of the list only. This end is called the top of the stack, and the other end is called the bottom of the stack.
69. Why is stack called as last-in-first-out?
Stack is called as last-in-first-out (LIFO), because the last data item placed on the stack is the first one removed when retrieval begins. The term push is used to describe placing a new item on the stack and pop is used to describe removing the top item from the stack.
70. What is a stack pointer?
Stack pointer (SP) is a processor register that is used to keep track of the address of the element of the stack that is at the top at any given time. It could be one of the general purpose registers or a register dedicated to this function.
71. What is a queue?
Queue is a data structure similar to the stack. Here new data are added at the back (high address end) and retrieved from the front (low address end) of the queue. Queue is also called as first-in-first-out (FIFO).
UNIT II
1.What is an n-bit ripple carry adder?
A cascaded connection of n full adder blocks, can be used to add two n-bit numbers. Since the carries must propagate, or ripple, through this cascade ,the configuration is called an n-bit ripple carry adder.
2.What are the two approaches to reduce delay in address?
To use fastest possible electronic technology in implementing the ripple-carry logic design or variations of it. To use an augmented logic gate network structure.
3.What is the purpose of using fast adder?
A fast adder circuit must speed up the generation of the carry signals.
4.What is Booth’s algorithm?
Booth’s algorithm is a technique for generating a 2 n-bit product. It treats both positive and negative 2’s complement n-bit operands uniformly.
5.List the two attractive features of Booth algorithm.
Booth algorithm has the following features.
-It handles both positive and negative multipliers uniformly.
-It achieves some efficiency in the number of additions required when the multiplier has a few large blocks of 1s.
6. What are the two techniques for speeding up multiplication operation?
To speed up multiplication operation, the techniques used are given below.
-The maximum number of summands that must be added is n/2 for n-nit operands.
-Reduces the time needed to add the summands.
7.Give the algorithm for performing restoring division.
The algorithm for performing restoring division is as follows.
a) Shift A and Q left one bit position.
b) Subtract M from A and place the answer back in A.
c) If the sign of A is 1. set q0 to 0 and add M back to A; otherwise set q0 to 1.
8.Give the algorithm for performing non-restoring division.
The algorithm for performing non-restoring division is given below.
Step 1:Do the following n times.
a) If the sign of A is 0,shift A and Q left one bit position and subtract M from A; otherwise , shift A and Q left and add M to A.
b) Now , if the sign A is 0,set q0 to 1;otherwise , set q0 to 0.
Step 2:If sign of A is 1.add M to A.
9. What are guard bits?
Guard bits are the extra bits retained during the intermediate steps which yield maximum accuracy in the final results.
10. Define a normalized number.
A normalized number is one in which the most significant digit of the significant is non-zero.
11.What is bit-pair recoding?
Bit-pair recoding of multipliers is a technique that halves the maximum number of summands .It is derived directly from Booth algorithm.
12.What are the techniques used the time needed to perform multiplication?
To reduce the time needed to perform multiplication, the techniques are,
- Bit-pair recoding of multiplier.
-Carry save addition of summands.
-Look ahead addition
13.What is chopping?
Chopping is a simple way to truncate or remove the guard bits and make no changes in the retained bits.
14.What is the process involved in Von-Neumann rounding?
If the bots to be removed are all 0s, they are simply dropped, with no changes to retained bits. However, if any of the bits to be removed are 1, the least significant bit of retained bit is set to 1.
15.Give the normalized number for base 2 representation.
For base 2 representation, a normalized number is one in which the most significant bit of the significant is one.
16.What are denormalized numbers?
Denormalized numbers are those numbers to handle cases of exponent underflow. When the exponent of the exponent of the result becomes too small, the result is denormalized by right ,shifting the fraction and incrementing the exponent for each shift, until the exponent within a representable range.
UNIT III
1. Define instruction set processor.
IR <-[[PC]]
The instruction recorder and control logic unit is responsible for implementing the actions specified by the instruction loaded in the IR register. The decoder generates the control signals needed to select the registers involved and direct the transfer of data. The registers, the ALU, and the interconnecting bus are collectively referred to as the data path
2. What are the three steps to execute an instruction?
To execute an instruction, the processor has to perform the following steps
1. Fetch the contents of the memory location pointed to by the PC. The content of this location are interpreted as an instruction to be executed. Hence, they are loaded into the IR. Symbolically this cab be written as
2. Assuming that the memory is byte addressable, increment the content of the PC by 4, that is,
PC<-[PC] +4
3. carry out the actions specified by the instruction in the IR
3. What are the uses of 3 register y, z and temp?
Y, z and temp are used by the processor for temporary storage during execution of some instructions. These register s are never used for storing data generated by one instruction for later use by another instruction.
4. Define data path.
1. Enable the output of register R1 by setting R1out to 1. This places the contents of R1 on the processor bus.
2. Enable the input of register R4 by setting R4in to 1. This loads data from the processor bus into register R4.
5. How will you transfer the contents of register R1 to register R4?
A technique called delayed branching can minimize the penalty incurred as a result of conditional branch
Instructions. The idea is simple. The instructions in the delay slots are always fetched. The processing unit, which executes machine instructions and coordinates the activities of other units. This unit is often called the instruction set processor (ISP), or simply the processor.
6. Define processor clock.
All operations and data transfers within the processor take place within time periods defined by the processor clock.
7. Define multiphase clocking.
Edge-triggered flip-flops are not used; two or more clock signals may be needed to guarantee proper transfer of data. This is known as multiphase clocking.
8. What are three steps that requires for the memory read operation?
R1out, MARin, Read
MDRinE, WMFC
MDRout, R2in
9. What are the actions that requires for executing of a complete instruction?
-Fetch the instruction
-Fetch the first operand (the contents of the memory location pointed to by R3).
-Perform the addition
-Load the result into RI
10. Define register file.
A three-bus structure used to connect the registers and the ALU of a processor. All general-purpose registers are combined into a single block called the register file.
11. Define control store.
The micro routines for all instructions in the instruction set of a computer are stored in a special memory called the control store.
12. Define vertical organization.
Highly encoded schemes that use compact codes to specify only a small number of control functions in each macro instruction are referred to as a vertical organization.
13. Define horizontal organization.
The minimally encoded scheme if in which many resources can be controlled with a single microinstruction is called a horizontal organization
14. Define bit-ORing technique.
The most efficient way to bypass microinstruction 170 is to have the preceding branch microinstruction specify the address 170 and then use an OR gate to change the least significant bit of this address to 1 if the direct addressing mode is involved. This is known as the bit-ORing technique
15. Define hazard.
Pipelined operation in is said to have been stalled for two clock cycles. Normal pipelined operation resumes in cycle 7.Any condition that causes the pipeline to stall is called a hazard.
16. Define control hazards.
The Pipeline may also be stalled because of a delay in the availability of an instruction. For example, this
may be a result of a miss in the cache, requiring the instruction to be fetched from the main memory. Such hazards are often called control hazards.
17. Define stalls.
The Decode unit is idle in cycle 3 through 5, the execute unit is idle in cycle 4 through 6 and the write unit is idle in cycle 5 through 7, such idle period are called stalls.
18. Define structural hazard.
Hazard that may be encountered in pipelined operation is known as a structural hazard.
19. What is meant by dispatch unit?
The instruction queue can store several instructions. A separate unit, which we call the dispatch unit, takes the instruction from the front of the queue and sends them to the execution unit.
20. Explain branch folding?
The instruction fetch unit has executed the branch instruction (by computing the branch address) concurrently with the execution of other instruction. This technique is referred as branch folding.
21. Define branch delay slot.
When execution of I2 is completed and a branch is to be made, the processor must discard I3 and fetch the instruction at the branch target. The location following a branch instruction is called a branch delay slot.
22. What is delayed branching?
A technique called delayed branching can minimize the penalty incurred as a result of conditional branch
instructions. The idea is simple. The instructions in the delay slots are always fetched.
23. Define static branch prediction.
With either of these schemes, the branch prediction decision is always the same every time a given instruction is executed. Any approach that has this characteristic is called static branch prediction
24. Define dynamic branch prediction.
Approach in which the prediction decision may change depending on execution history is called dynamic
branch prediction.
25. What is the address modes used in modem processors?
The addressing modes used in modern processors often have the following features:
-access to an operand does not require more than one access to the money
-only load and store instructions access memory operands
-The addressing modes used do not have side effects.
26. Define multiple-issue.
A more aggressive approach is to equip the processor with multiple processing units to handle several instructions in parallel in each processor stage. With this arrangement, several instructions start execution in the same clock, and the processor is said to use multiple-issue.
27. Define imprecise exceptions.
One or more of the succeeding instruction have been executed to completion. If such a situation is permitted the processor is said to have imprecise exceptions.
28. Define precise exception.
If an exception occurs during an instruction, all subsequent instructions that may have been partially executed are discarded. This is called a precise exception.
29. Define commitment unit.
When out-of-order execution is allowed, a special control unit is needed to guarantee in-order commitment. This is called commitment unit.
30. Explain deadlock?
A deadlock is a situation that can arise when two units, A and B use a shared resource. Suppose that unit B cannot complete its task unit A completes its task. At the same time, unit B has been assigned a resource that unit A need. If this happens, neither unit can complete its task. Unit A is waiting for the resource it needs, which is being held by unit B.
At the same time, unit B is waiting for unit A to finish before it can release that recourse.
UNIT IV
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 circuit 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?
The two parameters of performance are
Latency and Bandwidth
Latency : 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.
Band Width: 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. What is the purpose of the three different laser powers in CD-RW drive?
Highest power: Used to record the pits
Middle power (Erase power): Used to put the alloy into its crystalline state.
Lowest power: Used to read the stored information.
14. 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
15. 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.
16. What is the feature of Rambus memory?
The key feature of rambus technology is a fast signaling method used to transfer information between chips.
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:
1.They can store many Gigabytes
2.Less cost per bit
Flash Drive:
The capacity of flash drives is less than oneGB.
Higher cost per bit
29. Enumerate the advantages of flash drives.
Advantages:
Shorter seek and access time Faster 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 circuit 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 into 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.
Cache memory:
1. Cache memory bridges the speed gap between the processor and the main memory.
2. It is implemented in hardware
Virtual memory:
1. Virtual memory bridges the size and Speed gaps between the main memory and the secondary storage
2. It is implemented by software techniques
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?
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,
Seek
Read
Write
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,
Inexpensive
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:
Smaller & simpler.
Low cost.
Shipping convenience.
Disadvantages:
Longer access times.
Smaller storage capacities.
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?
Provides excellent performance
Large storage
Reliable
66. Enumerate the features of SCSI disks?
More expensive.
Exhibit better performance.
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:
Low price.
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,
Rewind and unload tape
Rewind tape
Erase tape
Write tape mark
Forward space one record
Backspace one record
Forward space one file
Backspace one file
72. What are the advantages of CD ROMs over magnetic disks?
Advantages:
Large storage capacity
Fast access times
Small physical size
Low cost
Easily transportable and removable
73.What is the purpose of the three different laser powers in CD-RW drive?
Highest power: Used to record the pits
Middle power (Erase power): Used to put the alloy into its crystalline state.
Lowest power: Used to read the stored information.
UNIT V
1.What are called memory-mapped I/O devices?
When I/O devices and the memory share the same address space the arrangement is called memory-mapped I/O devices.
2.What constitutes the device’s interface circuit?
The address decoder, the data and the status registers , and the control circuitry required to coordinate I/O transfers constitute the device’s interface circuit.
3.What are the two important mechanisms for implementing I/O operations?
There are two commonly used mechanisms for implementing I/O operations.They are interrupts and direct memory access.
4.What are known as interrupts?
In the case of interrupts, the synchronization is achieved by having the I/O device send a special signal over the bus whenever it is ready for a data transfer operation.
5.What do you mean by direct memory access?
Direct memory access is a technique used for high speed I/O devices. It involves having the device interface transfer data directly to or from the memory.
6.What do you mean by an interrupt- request line?
The bus control line is also known as an interrupt-request line.
7.What do you mean by an interrupt acknowledge signal?
The processor must inform the device that its request has been recognized so that it may remove its interrupt-request signal .This may be accomplished by an interrupt acknowledge signal.
8.What is a subroutine?
A subroutine performs a function required by the program from which it is called.
9.What is interrupt latency?
Saving registers also increases the delay between the time an interrupt request is received and the start of execution of the interrupt-service routine .This delay is called interrupt latency.
10.What is known as real-time processing?
The concept of interrupts is used in operating systems and in many control applications where processing of certain routines must be accurately timed relative to external events .The latter type of application is referred to as real-time processing.
11.What is known as a edge triggered line?
The processor has a special interrupt-request line for which the interrupt handling circuit responds only to the leading edge of a signal .such a line is called a edge-triggered line.
12.What is known as an interrupt vector?
The location pointed to by the interrupting device is used to store the starting address of the interrupt-service routine .The processor reads this address ,called the interrupt vector.
13.What is known as a debugger?
System software usually includes a program called a debugger, which helps the programmer find errors in a program.
14.What is an exception?
The term exception is often used to refer to any event that causes an interruption.
15.What are known as privileged instructions?
To protect the operating system of a computer from being corrupted by user programs, certain instructions can be executed only while the processor is in the supervisor mode. these are called privileged instructions.
16.What is known as multitasking?
Multitasking is a mode of operation in which a processor executes several user programs at the same time.
17.What is known as time slicing?
A common OS technique that makes multitasking possible is known as time slicing.
18.What is a process?
A program, together with any information that describes its current state of execution ,is regarded by the OS as an entity called a process.
19.What is a device driver?
A self contained module that encapsulates all software pertaining to a particular device is known as a device driver.
20.What is data abort?
Data abort arises from an error in reading or writing data.
21.What is known as prefetch abort?
Prefetch abort arises from an error when prefetching instructions from the memory.
22.What are banked registers?
The registers that replace user mode registers are called banked registers.
23.What is known as direct memory access?
A special control unit may be provided to allow transfer of a block of data directly between an external device and the main memory, without continuous intervention by the processor. This approach is called direct memory access, or DMA.
24.What is known as a DMA controller?
DMA transfers are performed by a control circuit that is part of the I/O device interface. This circuit is known as DMA controller.
25.What is known as cycle-stealing?
The processor originates most memory access cycles, the DMA controller can be said to “steal” memory cycles from the processor. Hence, this interweaving technique is usually called cycle stealing.
26.What is known as block/burst mode?
The DMA controller may be given exclusive access to the main memory to transfer a block of data without interrupt. This is known as block/burst mode.
27.What is called a bus master?
The device that is allowed to initiate data transfers on the bus at any given time is called the bus master.
28.What is known as distributed arbitration?
Distributed arbitration means that all devices waiting to use the bus have equal responsibility in carrying out the arbitration process, without using a central arbiter
29.What is a strobe?
Strobe captures the values of the data given instant and store them into a buffer.
30.What is meant by handshake?
Handshake is used between the master and the slave for controlling data transfers on the bus.
31. What is known as full handshake?
A change of state in one signal is followed by a change in the other signal. This is known as a full handshake.
32.What is a bitrate?
The speed of transmission is known as a bit rate.
33.What is a initiator?
A master is called an initiator in PCI technology.
34.What is called a target?
The addressed device that responds to read and write commands is called a target.
35.What is a transaction?
A complete transfer operation on the bus involving an address and a burst of data ,is called a transaction.
36.What are sectors?
Data are stored on a disk in blocks called sectors.
37.What are known as asynchronous events?
The event of pressing a key is not synchronized to any other event in a computer system. The data generated by the keyboard are called asynchronous.
38.What are known as isochronous events?
The sampling process yields a continuous stream of digitized samples that arrive at regular intervals, synchronized with the sampling clock.
39.What is known as plug- and- play ?
The plug-and –play feature means that a new device ,such as an additional speaker, can be connected at any time while the system is operating.
40.What is called a hub?
Each node of the tree has a device called a hub which acts as an intermediate control point between the host and the I/O devices.
41.What is a root hub?
At the root of a tree, a root hub connects the entire tree to the host computer.
42.What are called functions in USB terminology?
The leaves of the tree are the I/O devices being served which are called functions of the USB terminology.
43.What are called pipes?
The purpose of the USB software is to provide bi-directional communication links between application software and I/O devices. These links are called pipes.
44.What are called endpoints?
Locations in the device to or from which data transfer can take place ,such as status, control, and data registers are called endpoints.
45.What is a frame?
Devices that generate or receive isochronous data require a time reference to control the sampling process. To provide this reference, transmission over the USB is divided into frames of equal length.
46.What is the length of a frame?
A frame is 1 ms long for low-and full-speed data.
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