chapter 2: system unit: processing and memory.

coding systems are used to represnt data and programs in a manner that can be understood by the computers.

- Virtually all computers today are digital computers. —Such as the embedded computers, midrange servers, personal computers, mobile devices, mainframes, and supercomputers.- Most digital computers are binary computers. - this means that they can understand only two states, off and on. -represented by the digits 0 and 1.

-A numbering system is a way of representing numbers.-

-after numeric data is represented by the binary numbering system, text-based data isrepresented by binary coding systems-ASCII, EBCDIC, and Unicode. These codes are used to represent all characters that canappear in text data.

ASCII (American Standard Code for Information Interchange) is the coding systemtraditionally used with personal computers.

Unicode is a universal international coding standard designed to represent text-based data written in any ancient or modern language, including those withdifferent alphabets, such as Chinese, Greek, Hebrew, Amharic, Tibetan, and Russian.

-numeric and text-based data, which consists of alphanumeric characters and special symbols, such as the comma and dollar sign.

Graphics data consists of still images, such as photographs or drawings.- bitmap image an image comprised of a grid of small dots, called pixels

samples are digital representationsof the sound at particular moments.

is displayed using a collection of frames; each frame contains a still image. when they are played one after one.

Before a computer can execute any programinstruction, such as requesting input from the user, moving a file from one storage deviceto another, or opening a new window on the screen, it must convert the instruction intoa binary code known as machine language( directly quoted from the book).

The system unit is the main case of a computer.

A circuit board is a thin board containing computer chips and other electronic components.

The central processing unit (CPU) consists of a variety of circuitry and components that packaged together and connected directly to the motherboard. The CPU also calledthe microprocessor (when talking about personal computers) or just the processor

One measurement of the processing speed of a CPU is the CPU clock speed, which is typically rated in megahertz (MHz) or gigahertz (GHz).( directly quoted from the book).

A computer word is the amount of data(measured in bits or bytes) that a CPU canmanipulate at one time.

Cache memory is a special group of very fast memory circuitry located on or close tothe CPU.

bus is an electronic path over which data can travel.- bus width—the number ofwires in the bus over which data can travel.- The bus speed is also a very important factor, since the bus width and bus speed together determine the bus’s throughput or bandwidth

Memory refers to chip-based storage. or known as random access memory or RAM

called main memory, is used to store the essentialparts of the operating system while the computer is running.

A register is high-speed memory built into the CPU.

ROM (read-only memory) consists of nonvolatile chips that permanently store data orprograms.

Flash memory consists of nonvolatile memory chips that can be used for storage by thecomputer or the user.

fans, heat sinks (small components typically made out of aluminum with fins that help to dissipateheat),-other methods to cool the CPU and system unit.

Expansion slot. A location on the motherboard into which expansion cards are inserted.Expansion card. A circuit board that can beinserted into an expansion slot location on a computer’s motherboard to add additional functionality or to connect a peripheral device to thatcomputer.ExpressCard module. A module that can be inserted into a computer’s ExpressCard slot to add additional functionality or to connect aperipheral device to that computer; commonly used with notebook computers.

An electronic path on the motherboard or within the CPU or other computer component along which data is transferred.

memory bus is the change that allows forincreased performance; the bus used to connect the CPU to RAM is typically called the

"The frontside bus (FSB) connects the CPU to the chipset (most often called the I/O bridge today, though sometimes the older term Northbridge is still used) that connects the CPU to the rest of the bus architecture."

The PCI (Peripheral Component Interconnect) bus has been one of the most common types of expansion buses in past years.

" One of the more versatile bus architectures is the Universal Serial Bus (USB)."

" A high-speed bus standard often used to connect digital video cameras and other multimedia hardware to a computer."

port is a connector on the exterior of a computer to which a device may be attached.

This chapter explains how momory, CUPs, and other devices work.

There are several ways computer users can speed up their existing computers today.

Several strategies you can use to try to improve the performance of your current computer are discussed next.

more memory is required than was necessary even acouple of years ago.

uninstall programs to clean the computer from the fragments Delete the temporary filesError-check and defragment your hard driveScan for computer viruses and spyware continually."Clean out the dust from inside the system unit of desktop computers once or twicea year using a can of compressed air or a small vacuum cleaner."

hard drives become less efficient as they fill up. if it is full, buy more storage unites

"If your system seems slow primarily when you are using the Internet, the culprit might beyour Internet connection."

If programs, documents, and other items seem sluggish as they are displayed on yourmonitor, you can check to see if a video upgrade might help.

Researchers and manufacturers are using several strategies today to continue to build fasterand better personal computers.

Computer manufacturers are continually working to improve the basic architecture ofcomputers, such as to make them faster, cooler, quieter, more energy efficient, and morereliable.

" CPU chips used aluminum circuitry etched onto a silicon chip. As thenumber of aluminum circuits that can be packed onto a silicon chip without heat damageor interference approached its limit, chipmakers began to look for alternate materials."

The capability of a CPU to begin processing a new instruction as soon as the previous instruction completes the first stage of themachine cycle.

Selected trends we willlikely see more of in the near future are discussed next.

Nanotechnology. The science of creating tinycomputers and components by working at the individual atomic and molecular levels.

A technology that applies the principles of quantum physics and quantum mechanics to computers to direct atoms ornuclei to work together as quantum bits (qubits), which function simultaneously as the computer’s processor and memory

A computer that uses light, such as from laser beams or infrared beams, to perform digital computations.

Silicon photonics refers to the process of sending optical information among computersand other electronic devices using standard silicon manufacturing techniques

"The key element of the processor is the transistor" "the transister is a device made of semiconductor material that controls the flow of electrons inside a chip."

The architecture and components included in a CPU (referred to as microarchitecture) vary from processorto processor.

is the section of a CPU core that performs arithmetic involving integers and logical operations -Floating point unit (FPU).The part of a CPU core that performs decimal arithmetic.

"The control unit coordinates and controls the operations and activities taking place withina CPU core"

Prefetch unit: The part of a CPU core that attempts to retrieve data and instructions before they are needed for processing in order to avoid delays.

Decode Unit: The part of a CPU core that translates instructions into a form that can be processed by the ALU and FPU.

Registers are groups of high-speed memory located within the CPU that are usedduring processing.

Bus Interface Unit: The part of a CPU core that allows it to communicate with other CPU components.

System clock. The timing mechanism within the computer system that synchronizes the computer’s operations.Machine cycle. The series of operations involved in the execution of a single machine level instruction. 1. Fetch—the program instruction is fetched.2. Decode—the instructions are decoded so thecontrol unit, ALU, and FPU can understand them.3. Execute—the instructions are carried out.4. Store—the original data or the result from the ALUor FPU execution is stored in the CPU’s registers.