HARDWARE DATA AND PROGRAM REPRESENTATION Chapter Objective 1:
Most digital computers work in a two-state, or binary, fashion. It is convenient to think of
these binary states in terms of 0s and 1s. Computer people refer to these 0s and 1s as bits.
Converting data to these 0s and 1s is called digital data representation.
While most individuals use the decimal number system to represent numbers and
perform numeric computations, computers use the binary numbering system. Text-based
data can be represented with one of several fixed-length binary codes. Two possible coding schemes are ASCII (American Standard Code for Information Interchange) and EBCDIC (Extended Binary-Coded Decimal Interchange Code). These systems repre- sent single characters of data—a numeric digit, alphabetic character, or special symbol— as strings of bits. Each string of eight bits is called a byte. Unicode is a newer coding system that can represent text in all written languages, including those that use alphabets different from English, such as Chinese, Greek, and Russian.
The storage capacity of computers often is expressed in kilobytes (KB), or thousands of
bytes; megabytes (MB), millions of bytes; gigabytes (GB), billions of bytes; and terabytes (TB), trillions of bytes. Other possibilities are the petabyte (PB), about 1,000 terabytes; the exabyte (EB), about 1,000 petabytes; the zettabyte (ZB), about 1,000 exabytes; and the yottabyte (YB), about 1,000 zettabytes.
The binary system can represent not only text but also graphics, audio, and video data. Machine language is the binary-based code through which computers represent program instructions. A program must be translated into machine language before the computer can execute it. INSIDE THE SYSTEM UNIT Chapter Objective 2:
PCs typically contain a variety of hardware components located inside the system unit.
For instance, chips are mounted onto circuit boards, and those boards are positioned in
slots on the motherboard or system board—the main circuit board for a PC. Every PC has
a central processing unit (CPU)—also called a processor or a microprocessor when
referring to PCs—attached to its motherboard that performs the processing for the com-
puter. CPU chips differ in many respects, such as what types of PCs the CPU is designed
for, its clock speed, and word size. They can also be multi-core CPUs, such as the dual- core (two cores) and quad-core (four cores) CPUs now available. Another difference is the amount of cache memory—memory located on or very close to the CPU chip to help speed up processing. Other important differences are the general architecture of the CPU and the bus speed and width being used. The overall processing speed of the computer determines its performance. One of the most consistent measurements of overall perform- ance is a benchmark test.
The main memory chips for a PC are commonly referred to as RAM (random access memory). RAM is volatile and used to temporarily hold programs and data while they are needed. RAM is available in different types and speeds. ROM (read-only memory) are memory chips that store nonerasable programs. Flash memory is nonvolatile memory that can be erased and reprogrammed in blocks. Flash memory chips can be found in PCs and mobile devices; flash memory chips can also be used for storage with portable PCs, digital cameras, and other smaller devices. Registers are memory built into the CPU chip to hold data before or during processing.
CHAPTER 2 THE SYSTEM UNIT: PROCESSING AND MEMORY
Most desktop PCs contain internal expansion slots, into which users can insert Chapter Objective 3: expansion cards to give the computer added functionality. A computer bus is an electronic
path along which bits are transmitted. The parts of the system bus (the frontside bus and the
memory bus) move data between the CPU and RAM, and expansion buses connect the
CPU to peripheral devices. Common buses include PCI, PCI Express (PCIe), AGP, HyperTransport, Universal Serial Bus (USB), and FireWire.
System units typically have external ports that are used to connect peripheral devices
to the computer. Notebook and tablet PCs may have fewer ports than desktop PCs. Hand- held PC and mobile device users often add new capabilities with Secure Digital (SD) cards or other types of flash memory cards. ExpressCard modules can be used to add additional capabilities to PCs containing an ExpressCard slot. Some handheld PCs and mobile devices have a proprietary expansion system. HOW THE CPU WORKS
CPUs today include at least one arithmetic/logic unit (ALU), which performs integer Chapter Objective 4:
arithmetic and logical operations on data, and most include at least one floating point unit
(FPU), which performs decimal arithmetic. The control unit directs the flow of electronic
traffic between memory and the ALU/FPU and also between the CPU and input and output
devices. Registers—high-speed temporary holding places within the CPU that hold pro-
gram instructions and data immediately before and during processing—are used to enhance the computer’s performance. The prefetch unit requests data and instructions before or as they are needed, the decode unit decodes the instructions input into the CPU, internal cache stores frequently used instructions and data, and the bus interface unit inputs data and instructions from RAM.
The CPU processes instructions in a sequence called a machine cycle, consisting of
four basic steps. Each machine language instruction is broken down into several smaller instructions called microcode, and each piece of microcode corresponds to an operation (such as adding two numbers located in the CPU’s registers) that can be performed inside the CPU. The computer system has a built-in system clock that synchronizes all of the PC’s activities. MAKING COMPUTERS FASTER AND BETTER NOW AND IN THE FUTURE
There are several possible remedies for a computer that is performing too slowly, including
Chapter Objective 5:
adding more memory, performing system maintenance to clean up the PC’s hard drive,
buying a larger or additional hard drive, and upgrading the computer’s Internet connection
or video card, depending on the primary role of the computer and where the processing
bottleneck appears to be. To make computers work faster overall, computer designers have
developed a number of strategies over the years, and researchers are continually working on new strategies. Some of the strategies already being implemented include improved architecture, pipelining, multiprocessing, parallel processing, and the use of improved materials.
One possibility for future computers is nanotechnology research, which focuses on Chapter Objective 6:
building computer components at the individual atomic and molecular levels. Some
products (such as NRAM and bikes) using carbon nanotubes are currently on the market. Quantum computing and optical computers are other possibilities being researched,
along with three-dimensional (3D) chips.
Brief CV of M A Zanjanchi Biography: Date of birth: June 1954 Place of birth: Ghazvin, Iran Nationality: Iranian Marital status: Married, two daughters and one son Affiliation and working address: Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box 1914, Rasht, Iran Tel: 0131-3243630-5 Fax: 0131-3220066 E-mail Academic Ranks: Assistant Prof. 1982-1996 A
The efficacy of a four-week, ofloxacin-containingregimen compared with standard WHO-MDTin PB leprosyM A R I V I C F . B A L A G O N * , R O L A N D V . C E L L O N A * ,R O D O L F O M. AB A L O S * , RO B E R T H . G E L B E R* *& PA UL R . SA UND ERSO N**Leonard Wood Memorial Center for Leprosy Research,**University of California, San Francisco, USAAccepted for publication 24 November 20