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C952 - COMPUTER ARCHITECTURE
EXAM QUESTIONS WITH RIGHT
ACCURATE ANSWERS.
Personal computer (PC) - correct Answers - A computer designed for use by an individual, usually incorporating a graphics display, a keyboard, and a mouse. Server - correct Answers - A computer used for running larger programs for multiple users, often simultaneously, and typically accessed only via a network. Supercomputer: - correct Answers - A class of computers with the highest performance and cost; they are configured as servers and typically cost tens to hundreds of millions of dollars. Embedded computer: - correct Answers - A computer inside another device used for running one predetermined application or collection of software. Personal mobile devices (PMDs) - correct Answers - are small wireless devices to connect to the Internet; they rely on batteries for power, and software is installed by downloading apps. Conventional examples are smart phones and tablets. Cloud computing - correct Answers - refers to large collections of servers that provide services over the Internet; some providers rent dynamically varying numbers of servers as a utility. Software as a Service (SaaS) - correct Answers - delivers software and data as a service over the Internet, usually via a thin program such as a browser that runs on local client devices, instead of binary code that must be installed, and runs wholly on that device. Examples include web search and social networking.
Multicore microprocessor - correct Answers - A microprocessor containing multiple processors ("cores") in a single integrated circuit. Acronym - correct Answers - A word constructed by taking the initial letters of a string of words. For example: RAM is an acronym for Random Access Memory, and CPU is an acronym for Central Processing Unit. Terabyte (TB): - correct Answers - Originally 1,099,511,627,776 (240) bytes, although communications and secondary storage systems developers started using the term to mean 1,000,000,000,000 (1012) bytes. To reduce confusion, we now use the term tebibyte (TiB) for 240 bytes, defining terabyte (TB) to mean 1012 bytes. The figure below shows the full range of decimal and binary values and names. Systems software: - correct Answers - Software that provides services that are commonly useful, including operating systems, compilers, loaders, and assemblers. Operating system - correct Answers - Supervising program that manages the resources of a computer for the benefit of the programs that run on that computer. Compiler - correct Answers - A program that translates high-level language statements into assembly language statements. Binary digit - correct Answers - Also called a bit. One of the two numbers in base 2 (0 or 1) that are the components of information. Instruction - correct Answers - A command that computer hardware understands and obeys Assembler - correct Answers - A program that translates a symbolic version of instructions into the binary version. Assembly language - correct Answers - A symbolic representation of machine instructions.
Control - correct Answers - The component of the processor that commands the datapath, memory, and I/O devices according to the instructions of the program. Memory - correct Answers - The storage area in which programs are kept when they are running and that contains the data needed by the running programs. Dynamic random access memory (DRAM) - correct Answers - Memory built as an integrated circuit; it provides random access to any location. Access times are 50 nanoseconds and cost per gigabyte in 2012 was $5 to $10. Cache memory - correct Answers - A small, fast memory that acts as a buffer for a slower, larger memory. Static random access memory (SRAM): - correct Answers - Also memory built as an integrated circuit, but faster and less dense than DRAM. Instruction set architecture - correct Answers - Also called architecture. An abstract interface between the hardware and the lowest-level software that encompasses all the information necessary to write a machine language program that will run correctly, including instructions, registers, memory access, I/O, and so on. Application binary interface (ABI) - correct Answers - The user portion of the instruction set plus the operating system interfaces used by application programmers. It defines a standard for binary portability across computers. Implementation - correct Answers - Hardware that obeys the architecture abstraction Volatile memory - correct Answers - Storage, such as DRAM, that retains data only if it is receiving power. Nonvolatile memory - correct Answers - A form of memory that retains data even in the absence of a power source and that is used to store programs between runs. A DVD disk is nonvolatile.
Main memory - correct Answers - Also called primary memory. Memory used to hold programs while they are running; typically consists of DRAM in today's computers. Secondary memory - correct Answers - Nonvolatile memory used to store programs and data between runs; typically consists of flash memory in PMDs and magnetic disks in servers. Magnetic disk - correct Answers - Also called hard disk. A form of nonvolatile secondary memory composed of rotating platters coated with a magnetic recording material. Because they are rotating mechanical devices, access times are about 5 to 20 milliseconds and cost per gigabyte in 2012 was $0.05 to $0.10. Flash memory - correct Answers - A nonvolatile semiconductor memory. It is cheaper and slower than DRAM but more expensive per bit and faster than magnetic disks. Access times are about 5 to 50 microseconds and cost per gigabyte in 2012 was $0.75 to $1.00. Local area network (LAN) - correct Answers - A network designed to carry data within a geographically confined area, typically within a single building Wide area network (WAN) - correct Answers - A network extended over hundreds of kilometers that can span a continent Transistor - correct Answers - An on/off switch controlled by an electric signal. Very large-scale integrated (VLSI) circuit: - correct Answers - A device containing hundreds of thousands to millions of transistors Silicon - correct Answers - A natural element that is a semiconductor Semiconductor - correct Answers - A substance that does not conduct electricity well. Silicon crystal ingot - correct Answers - A rod composed of a silicon crystal that is between 8 and 12 inches in diameter and about 12 to 24 inches long.
Clock cycles per instruction (CPI): - correct Answers - Average number of clock cycles per instruction for a program or program fragment. Instruction count - correct Answers - The number of instructions executed by the program. Instruction mix: - correct Answers - A measure of the dynamic frequency of instructions across one or many programs. Workload - correct Answers - A set of programs run on a computer that is either the actual collection of applications run by a user or constructed from real programs to approximate such a mix. A typical workload specifies both the programs and the relative frequencies. Benchmark - correct Answers - A program selected for use in comparing computer performance. Amdahl's Law - correct Answers - A rule stating that the performance enhancement possible with a given improvement is limited by the amount that the improved feature is used. It is a quantitative version of the law of diminishing returns. Million instructions per second (MIPS) - correct Answers - A measurement of program execution speed based on the number of millions of instructions. MIPS is computed as the instruction count divided by the product of the execution time and 106. Instruction set: - correct Answers - The vocabulary of commands understood by a given architecture. Stored-program concept - correct Answers - The idea that instructions and data of many types can be stored in memory as numbers and thus be easy to change, leading to the stored-program computer. Word - correct Answers - A natural unit of access in a computer, usually a group of 32 bits.
Doubleword - correct Answers - Another natural unit of access in a computer, usually a group of 64 bits; corresponds to the size of a register in the LEGv8 architecture. Data transfer instruction - correct Answers - A command that moves data between memory and registers. Address - correct Answers - A value used to delineate the location of a specific data element within a memory array. Alignment restriction - correct Answers - A requirement that data be aligned in memory on natural boundaries. Binary digit - correct Answers - Also called binary bit. One of the two numbers in base 2, 0 or 1, that are the components of information. Least significant bit - correct Answers - The rightmost bit in an LEGv8 doubleword Most significant bit - correct Answers - The leftmost bit in an LEGv8 doubleword. Two's complement - correct Answers - A signed number representation where a leading 0 indicates a positive number and a leading 1 indicates a negative number. The complement of a value is obtained by complementing each bit (0 → 1 or 1 → 0), and then adding one to the result (explained further below). One's complement - correct Answers - A notation that represents the most negative value by 10 ... 000two and the most positive value by 01 ... 11two, leaving an equal number of negatives and positives but ending up with two zeros, one positive (00 ... 00two) and one negative ( ... 11two). The term is also used to mean the inversion of every bit in a pattern: 0 to 1 and 1 to 0. Biased notation - correct Answers - A notation that represents the most negative value by 00 ... 000two and the most positive value by 11 ... 11two, with 0 typically having the value 10 ... 00two, thereby biasing the number such that the number plus the bias has a non-negative representation.
Procedure - correct Answers - A stored subroutine that performs a specific task based on the parameters with which it is provided. Branch-and-link instruction - correct Answers - An instruction that branches to an address and simultaneously saves the address of the following instruction in a register (LR or X30 in LEGv8). Return address - correct Answers - A link to the calling site that allows a procedure to return to the proper address; in LEGv8 it is stored in register LR (X30). Caller - correct Answers - The program that instigates a procedure and provides the necessary parameter values. Callee - correct Answers - A procedure that executes a series of stored instructions based on parameters provided by the caller and then returns control to the caller. Program counter (PC) - correct Answers - The register containing the address of the instruction in the program being executed. Stack - correct Answers - A data structure for spilling registers organized as a last-in- first-out queue. Stack pointer - correct Answers - A value denoting the most recently allocated address in a stack that shows where registers should be spilled or where old register values can be found. In LEGv8, it is register SP. Push - correct Answers - Add element to stack Pop - correct Answers - Remove element from stack. Global pointer - correct Answers - The register that is reserved to point to the static area
Procedure frame - correct Answers - Also called activation record. The segment of the stack containing a procedure's saved registers and local variables Frame pointer - correct Answers - A value denoting the location of the saved registers and local variables for a given procedure. Text segment - correct Answers - The segment of a UNIX object file that contains the machine language code for routines in the source file PC-relative addressing - correct Answers - An addressing regime in which the address is the sum of the program counter (PC) and a constant in the instruction. Addressing mode - correct Answers - One of several addressing regimes delimited by their varied use of operands and/or addresses. Data race - correct Answers - Two memory accesses form a data race if they are from different threads to same location, at least one is a write, and they occur one after another. Assembly language - correct Answers - A symbolic language that can be translated into binary machine language. Pseudoinstruction - correct Answers - A common variation of assembly language instructions often treated as if it were an instruction in its own right. Symbol table - correct Answers - A table that matches names of labels to the addresses of the memory words that instructions occupy. Linker - correct Answers - Also called link editor. A systems program that combines independently assembled machine language programs and resolves all undefined labels into an executable file.
Static method - correct Answers - A method that applies to the whole class rather to an individual object. It is unrelated to static in C. General-purpose register (GPR): - correct Answers - A register that can be used for addresses or for data with virtually any instruction. Accumulator: - correct Answers - Archaic term for register. On-line use of it as a synonym for "register" is a fairly reliable indication that the user has been around quite a while. Load-store architecture - correct Answers - Also called register-register architecture. An instruction set architecture in which all operations are between registers and data memory may only be accessed via loads or stores. Arithmetic Logic Unit (ALU) - correct Answers - Hardware that performs addition, subtraction, and usually logical operations such as AND and OR Dividend: - correct Answers - A number being divided. Divisor: - correct Answers - A number that the dividend is divided by. Quotient: - correct Answers - The primary result of a division; a number that when multiplied by the divisor and added to the remainder produces the dividend. Remainder - correct Answers - The secondary result of a division; a number that when added to the product of the quotient and the divisor produces the dividend. Scientific notation - correct Answers - A notation that renders numbers with a single digit to the left of the decimal point. Normalized - correct Answers - A number in floating-point notation that has no leading 0s
Floating point - correct Answers - Computer arithmetic that represents numbers in which the binary point is not fixed Fraction: - correct Answers - The value, generally between 0 and 1, placed in the fraction field. The fraction is also called the mantissa. Exponent - correct Answers - In the numerical representation system of floating-point arithmetic, the value that is placed in the exponent field Overflow (floating-point) - correct Answers - A situation in which a positive exponent becomes too large to fit in the exponent field. Underflow (floating-point): - correct Answers - A situation in which a negative exponent becomes too large to fit in the exponent field. Double precision: - correct Answers - A floating-point value represented in a 64-bit doubleword. Single precision - correct Answers - A floating-point value represented in a 32-bit word Exception - correct Answers - Also called interrupt. An unscheduled event that disrupts program execution; used to detect overflow. Interrupt: - correct Answers - An exception that comes from outside of the processer. (Some architectures use the term interrupt for all exceptions. Guard: - correct Answers - The first of two extra bits kept on the right during intermediate calculations of floating-point numbers; used to improve rounding accuracy. Round - correct Answers - Method to make the intermediate floating-point result fit the floating- point format; the goal is typically to find the nearest number that can be represented in the format. It is also the name of the second of two extra bits kept on the right during intermediate floating-point calculations, which improves rounding accuracy.
Program counter (PC): - correct Answers - The register containing the address of the instruction in the program being executed. Register file - correct Answers - A state element that consists of a set of registers that can be read and written by supplying a register number to be accessed. Sign-extend - correct Answers - To increase the size of a data item by replicating the high-order sign bit of the original data item in the high-order bits of the larger, destination data item. Branch target address - correct Answers - The address specified in a branch, which becomes the new program counter (PC) if the branch is taken. In the LEGv8 architecture, the branch target is given by the sum of the offset field of the instruction and the address of the branch. Branch taken - correct Answers - A branch where the branch condition is satisfied and the program counter (PC) becomes the branch target. All unconditional branches are taken branches. Branch not taken or (untaken branch): - correct Answers - A branch where the branch condition is false and the program counter (PC) becomes the address of the instruction that sequentially follows the branch. Truth table - correct Answers - From logic, a representation of a logical operation by listing all the values of the inputs and then in each case showing what the resulting outputs should be. Don't-care term: - correct Answers - An element of a logical function in which the output does not depend on the values of all the inputs. Don't-care terms may be specified in different ways. Opcode: - correct Answers - The field that denotes the operation and format of an instruction. Single-cycle implementation - correct Answers - Also called single clock cycle implementation. An implementation in which an instruction is executed in one clock cycle. While easy to understand, it is too slow to be practical.
Pipelining: - correct Answers - An implementation technique in which multiple instructions are overlapped in execution, much like an assembly line. Structural hazard: - correct Answers - When a planned instruction cannot execute in the proper clock cycle because the hardware does not support the combination of instructions that are set to execute. Data hazard: - correct Answers - Also called a pipeline data hazard. When a planned instruction cannot execute in the proper clock cycle because data that is needed to execute the instruction are not yet available. Forwarding: Also called bypassing. - correct Answers - A method of resolving a data hazard by retrieving the missing data element from internal buffers rather than waiting for it to arrive from programmer-visible registers or memory. Load-use data hazard: - correct Answers - A specific form of data hazard in which the data being loaded by a load instruction has not yet become available when it is needed by another instruction. Pipeline stall: Also called bubble - correct Answers - A stall initiated in order to resolve a hazard Control hazard: Also called branch hazard - correct Answers - When the proper instruction cannot execute in the proper pipeline clock cycle because the instruction that was fetched is not the one that is needed; that is, the flow of instruction addresses is not what the pipeline expected. Branch prediction - correct Answers - A method of resolving a branch hazard that assumes a given outcome for the conditional branch and proceeds from that assumption rather than waiting to ascertain the actual outcome. Latency (pipeline) - correct Answers - The number of stages in a pipeline or the number of stages between two instructions during execution
Imprecise interrupt: Also called imprecise exception - correct Answers - Interrupts or exceptions in pipelined computers that are not associated with the exact instruction that was the cause of the interrupt or exception Precise interrupt: Also called precise exception - correct Answers - An interrupt or exception that is always associated with the correct instruction in pipelined computers. Instruction-level parallelism: - correct Answers - The parallelism among instructions Multiple issue - correct Answers - A scheme whereby multiple instructions are launched in one clock cycle. Static multiple issue: - correct Answers - An approach to implementing a multiple-issue processor where many decisions are made by the compiler before execution. Dynamic multiple issue - correct Answers - An approach to implementing a multiple-issue processor where many decisions are made during execution by the processor. Issue slots: - correct Answers - The positions from which instructions could issue in a given clock cycle; by analogy, these correspond to positions at the starting blocks for a sprint. Instruction-level parallelism: - correct Answers - The parallelism among instructions. Multiple issue - correct Answers - A scheme whereby multiple instructions are launched in one clock cycle. Static multiple issue - correct Answers - An approach to implementing a multiple-issue processor where many decisions are made by the compiler before execution. Dynamic multiple issue - correct Answers - An approach to implementing a multiple-issue processor where many decisions are made during execution by the processor.
Speculation: - correct Answers - An approach whereby the compiler or processor guesses the outcome of an instruction to remove it as a dependence in executing other instructions. Issue packet: - correct Answers - The set of instructions that issues together in one clock cycle; the packet may be determined statically by the compiler or dynamically by the processor. Very Long Instruction Word (VLIW - correct Answers - A style of instruction set architecture that launches many operations that are defined to be independent in a single wide instruction, typically with many separate opcode fields. Use latency - correct Answers - Number of clock cycles between a load instruction and an instruction that can use the result of the load without stalling the pipeline. Loop unrolling - correct Answers - A technique to get more performance from loops that access arrays, in which multiple copies of the loop body are made and instructions from different iterations are scheduled together. Register renaming - correct Answers - The renaming of registers by the compiler or hardware to remove antidependences. Antidependence: - correct Answers - An ordering forced by the reuse of a name, typically a register, rather than by a true dependence that carries a value between two instructions. Superscalar: - correct Answers - An advanced pipelining technique that enables the processor to execute more than one instruction per clock cycle by selecting them during execution. Dynamic pipeline scheduling - correct Answers - Hardware support for reordering the order of instruction execution to avoid stalls. Commit unit - correct Answers - The unit in a dynamic or out-of-order execution pipeline that decides when it is safe to release the result of an operation to programmer-visible registers and memory
