Computer Science (Chapter 4-5)

Megabyte

2^20 (a little more than a million) bytes.

Types of Gates

A NOT gate inverts its single input value. An AND gate produces 1 if both input values are 1. An OR gate produces 1 if one or the other or both input values are 1. An XOR gate produces 1 if one or the other (but not both) input values are 1. A NAND gate produces the opposite results of an AND gate. A NOR gate produces the opposite results of an OR gate.

Half Adder

A circuit that computes the sum of two bits and produces the appropriate carry bit.

Full Adder

A circuit that computes the sum of two bits, taking an input carry bit into account.

Multiplexer

A circuit that uses a few input control signals to determine which of several input data lines is routed to its output.

Sequential Circuit

A circuit whose output is a function of its input values and the current state of the circuit.

Combinational Circuit

A circuit whose output is solely determined by its input values.

Circuit

A combination of interacting gates designed to accomplish a specific logical function.

Track

A concentric circle on the surface of a disk (pg.135).

Input Unit

A device that accepts data to be stored in memory. The medium by which data and programs from the outside world are entered into the computer.

Transistor

A device that acts either as a wire or a resistor, depending on the voltage level of an input signal. It's like a switch and it is made of semiconductor material. Usually silicon is used to create them.

Gate

A device that performs a basic operation on electronic signals, accepting one or more input signals and producing a single output signal.

Output Unit

A device through which results stored in the computer memory are made available to the outside world. The most common of these devices are displays and printers.

NOT Gate

A gate which accepts only one input value and produces only one output value. If the input value is 1, then the output value is 0. And if the input value is 0, then the output value is 1. The logic diagram symbol for this gate is a triangle with a small circle on the end (called an inversion bubble). This gate is sometimes called an inverter because it inverts the input value.

Logic Diagram

A graphical representation of a circuit; each type of gate has its own symbol.

Virtual Computer

A hypothetical machine designed to illustrate important features of a real machine.

AND Gate

A logic gate which accepts two input signals. The values of both input signals determine what the output signal will be. If the two input values are both 1 then the output is 1; otherwise, the output is 0.

OR Gate

A logic gate which accepts two input values. If both input values are 0, the output value is 0; otherwise, the output is 1 for any other combination of inputs.

XOR Gate

A logic gate which produces a 0 if its two inputs are the same, and if they're not, then the output is 1. This gate produces a 1 only if its inputs are mixed (one 1 and one 0). Think of this gate as saying, "When I say or, I mean one or the other, not both."

Assembly Language

A low-level programming language in which a mnemonic represents each of the machine-language instructions for a particular computer.

Boolean Algebra

A mathematical notation for expressing two-valued logical functions. A form of algebra in which variables and functions take on only one of two possible values (0 and 1).

Integrated Circuit

A piece of silicon on which multiple gates have been embedded (chip).

Loader

A piece of software that takes a machine language program and places it into memory.

Giga

A prefix that means one billion.

Mega

A prefix that means one million.

Superscalar

A processor that recognizes the chance to simultaneously operate on different parts of an instruction. It sends instructions to different execution units (i.e. two ALUs operating at the same time).

Assembler

A program that translates an assembly-language program in machine code.

Sector

A section of a track (pg.135).

Register

A small storage area in the CPU used to store intermediate values or special data. These registers contain one word (16-bit) and are used to store information that is needed again immediately.

Cache Memory

A small, fast memory that is usually built into the processor chip (not using the FSB). Most of the processor's attempts to access memory will find what they need within this type of memory.

Program Counter

A special register in the control unit that contains the address of the next instruction to be executed.

Instruction Register

A special register in the control unit that contains the instruction that is being executed.

Truth Table

A table showing all possible input values and the associated output values.

Pipelining

A technique that speeds up the fetch-execute cycle by breaking an instruction into smaller steps that can be overlapped.

Cache Memory

A type of small, high-speed memory used to hold frequently used data. Many memory accesses are very time consuming relative to the speed of the processor, hence many architectures provide this type of memory to alleviate the issue.

Hertz

A unit of frequency that measures cycles per second, abbreviated Hz. It is named after Heinrich R. Hertz.

2 MP

Abbreviated for 2 million pixels, indicating that the resolution is 2 million pixels.

GPU

Acronym for graphics processing unit, a separate computer that can be even more powerful than the main processors. Games and other graphics software send commands that cause it to manipulate the image on the screen quickly (relieves the main processors from this task). Also, it keeps the data for the screen image in its own memory.

Parallel Architecture

An architecture with more than one processor.

Adder

An electronic circuit that performs an addition operation on binary values.

NAND Gate

An inversion/negation of the AND gate. The output of this gate is the same as if you took the AND gate and put it through an inverter (a NOT gate). The logic diagram symbol for this gate is the same as the AND gate except it uses an inversion bubble (to indicate negation).

NOR Gate

An inversion/negation of the OR gate. The output of this gate is the same as if you took the OR gate and put it through an inverter (a NOT gate). The logic diagram symbol for this gate is the same as the OR gate except it uses an inversion bubble (to indicate negation). The output values in the truth table for this gate would be opposite of the OR gate's outputs.

ALU

Arithmetic/logic unit, the computer component that performs arithmetic operations (addition, subtraction, multiplication, division) and logical operations (AND, OR and NOT).

Bit-level Parallelism

Based on increasing the word size of a computer (now we use 64-bit processors). A 16-bit processor can process a 16-bit data value in one single instruction, but an 8-bit processor will do it in two operations. Thus, increasing the word size reduces the number of operations on data values larger than the word size.

Instruction-level Parallelism

Based on the idea that some instructions in a program can be carried out independently in parallel. For example, if a program requires operations on unrelated data, these operations can be done at the same time.

Hard Disk Drive

Common name for the computer's auxiliary storage device (secondary storage).

George Boole

Considered one of the founders of computer science due to his contribution to logic and ________ algebra. He was very bright even at a young age. He published books and articles which were phenomenal, although they did not receive much attention at the time.

Second Step of the Fetch Cycle

Decode the instruction: Control unit determines what instruction it is by decoding it into control signals (the logic of the circuitry in the CPU determines which operation is to be executed).

DDR2

Double-data rate (second generation).

Fourth Step of the Fetch Cycle

Execute the instruction: This involves sending signals to the arithmetic/logic unit (ALU) to carry out the processing. In the case of adding a number to a register, the operand (data) is sent to the ALU and added to the contents of the register.

Comment

Explanatory text for the human reader.

First Step of the Fetch Cycle

Fetching the next instruction: Control unit goes to the address in memory specified at the Program Counter (PC), makes a copy of the contents and places the copy in the Instruction Register (IR). Next the PC is updated to hold the next instruction (incremented) by control unit.

Third Step of the Fetch Cycle

Get data if needed: Control unit gets additional memory accesses, if it's necessary to complete the task.

Clock

In a computer, a centrally generated series of electrical pules. It is used to ensure that all of its actions are coordinated. You can think of this like an orchestra conductor's waving baton, which keeps all of the musicians playing together at a particular tempo.

Instruction Specifier

Indicates which operation is to be carried out, such as "add a number to a value already stored in a register," and how to interpret just where the operand is.

Assembler Directives

Instructions to the translating program.

von Neumann architecture

Main parts: memory, the arithmetic/logic unit (ALU), input devices, output devices, and the control unit. This is the underlying architecture of most of today's computers.

Semiconductor

Material such as silicon that is neither a good conductor nor a good insulator.

Synchronous Processing

Multiple processors apply the same program in lock-step to multiple data sets. For example, increasing the brightness of an image involves adding a value to every one of several million pixels. These additions can all be done in parallel (pg. 141).

ROM

Read-only memory, unlike RAM the contents in this memory cannot be changed (ROM is not volatile, but RAM is). This type of memory is permanent and cannot be altered by a stored operation. Its contents are created by the process called burning and burning happens when the computer parts are first assembled.

RPM

Revolutions per minute.

SATA

Serial ATA, an interface for hard disk drives which is faster and cheaper than parallel ATA . Serial means that its data is transmitted to and from the computer as a stream of individual bits, rather than the older approach of sending 16 bits at once over 16 wires (known as parallel ATA).

SSD

Solid-state disk, a new replacement to hard drives. It uses all-electronic secondary storage, this technology is similar to the RAM except the data isn't lost when the power is turned off. Since it has no moving parts, it is faster and consumes less power.

Central Processing Unit

The CPU, a combination of the arithmetic/logic unit (ALU) and the control unit; the "brain of a computer that interprets and executes instructions.

Front Side Bus

The bus that makes the primary connection between the processor and the outside world, abbreviated FSB.

Control Unit

The computer component that controls the actions of the other components so as to execute instructions in sequence. It is the organizing force in the computer, for it is in charge of the fetch-execute cycle.

RAM

The computer's random access memory, also called the main memory. Random access means that each byte of memory can be accessed directly, rather than having to begin at the beginning and access each byte in turn until you get the one you want.

Block

The information stored in a sector (pg.135).

Machine Language

The language made up of binary-coded instructions that is used directly by the computer.

Motherboard

The main circuit board of a personal computer. The components in a von Neumann machine reside physically on this printed circuit board.

Bus

The medium by which the processor accesses memory and input/output (I/O) devices.

Addressability

The number of bits stored in each addressable location in memory.

Bus Width

The number of bits that can be transferred in parallel over the bus. The wider the bus, the more address or data bits it can move at once.

Transfer Rate

The rate at which data is transferred from the disk to memory.

Circuit Equivalence

The same output for each corresponding input-value combination for two circuits.

Cylinder

The set of concentric tracks on all surfaces.

Shared Memory Parallel Processor

The situation in which multiple processors share a global memory.

Access Time

The time it takes for a block to start being read; the sum of seek time and latency.

Seek Time

The time it takes for the read/write head to get positioned over the specified track.

Latency

The time it takes for the specified sector to spin into position under the read/write head. Also called rotation delay because the average time for this to occur happens at one-half the rotation of the disk.

Address

Used to select the memory location or device to which data will go, or from which it will be taken.

Volatile

When the bit configurations in the memory do not remain the same and are not permanent. Turning off the power does not retain the previous bit configurations. RAM is an example.