Text 2.

“Hardware”

The functions of the hardware composing a computer can be divided broadly into the following five categories: Input; Storage; Operation; Control and Output.

The following are the units that implement the above-mentioned functions:

· Input unit: This unit inputs the data and programs for computer processing. It is equivalent to the human eyes and ears.

· Storage unit: This unit stores the input data and programs. It is equivalent to the memory section of the human brain.

· Arithmetic unit: This unit conducts calculation and decision on the stored data according to the instructions of the program. It is equivalent to the thinking section of the human brain.

· Control unit: This unit controls the input unit, storage unit, arithmetic unit and the output unit. It is equivalent to the human central nervous system.

· Output unit: This unit outputs the results of computer processing in a format that can be understood by humans. It is equivalent to the human hands and mouth.

These five units are called the "computer five main units".

Since the control unit and the arithmetic unit are handled as one unit, they are called the processor (processing unit) or central processing unit (CPU). The general term "peripheral devices" is used to refer to the input unit, the output unit and the auxiliary storage devices that are outside the processor and exchange data with the main storage unit.

Likewise, the storage units are divided into main storage unit and auxiliary storage device, depending on their functions.

(1)    RAM (Random Access Memory)

The RAM is semiconductor memory in which data writing and reading is possible. When the computer is turned off, the stored data is lost. This property is called volatility. Since most main storage units are composed of RAMs, the processor can be made to read and write information from the main storage unit at random by specifying the address.

RAMs are classified into DRAMs and SRAMs.

1)DRAM (Dynamic RAM)

A DRAM represents bits, and stores information depending on whether the part called capacitor is being charged (status "1") or is not being charged (status "0").

Since the circuits are simple and small, RAMs of large capacity can be created at low cost. However, since the charge stored in the capacitor is lost after a lapse of time, the memory needs to be rewritten (recharged) at regular intervals. This operation is called refreshing. Once, DRAMs were used in the main storage unit, but currently they are also used in storage units, etc., contained in the input/output units of printers and other devices.

          2)SDRAM (Synchronous DRAM)

Due to the progress of IC technology, and the consequent substantial improvement of the performance of processors, the operating speed of the DRAMs that composed the storage unit could not keep up with the operating speed of the processors. For that reason, an external clock signal that indicates the processor operation timing is now set in the DRAM and through synchronization with this signal, complicated address specifications are reduced and simplified, enabling the development of DRAMs that operate at high speeds. These types of DRAMs are called synchronous DRAMs (SDRAM).

3)SRAM (Static RAM)

SRAMs are created with a circuit called the flip-flop. The flip-flop settles the output according to the previous input and the current input, and can preserve the status "1" and "0" inside the circuit. Since data is not lost unless the computer is turned off, memory refreshing is not necessary. However, since SRAM circuits are complicated, the memory capacity is smaller than that of DRAMs and the cost is higher. However, since its processing speed is high, it is used in devices such as the registers contained in main storage units and processors.

(2)    ROM (Read Only Memory)

The ROM is semiconductor memory for read use only. Since programs and data are stored in the ROM from the beginning, the stored information is not lost even if the computer is turned off. This property is called nonvolatility.

ROMs are classified into mask ROMs and user programmable ROMs.

          1)Mask ROM

Since programs and data are already written in the Mask ROM before it is shipped by the manufacturer, the user cannot add any programs or data. Mask ROMs are used in the memories of game cassettes and IPL (Initial Program Loader), a program used to start the computer, etc.

2)User programmable ROM

The user programmable ROM is a type of ROM, but since at the time it is shipped by the manufacturer it has nothing stored in it, the user can write data into it once. The following types of user programmable ROM exist

·   PROM (Programmable ROM): Once data has been written, it cannot be erased.

·   EPROM (Erasable PROM): It can be erased with ultraviolet light and rewritten.

·   EEPROM (Electrically Erasable PROM): It can be erased through the application of electrical voltage and rewritten.

EEPROM is used in a storage medium called flash memory, which is used in the registration of image data of digital cameras, etc. Likewise, it is also used in the storage section of IC cards, etc.

Text 1.

The summary of the book:The Irwin handbook of Telecommunications

The book is divided into five parts, as were previous editions, corresponding to major divisions in telecommunications equipment. Chapter One is an introduction to voice and data. The remainder of Part One is devoted to concepts that are common to the industry. In Part One, we discuss voice and data fundamentals, pulse code modulation, outside plant, structured wiring, access technologies, local area network principles, and the other building blocks of telecommunication networks.

Part Two covers switching. The part begins with a discussion of signaling, including new protocols Session Initiation Protocol (SIP) and ENUM, which are new since the last edition, and hold considerable promise for the future. A chapter on the public switched telephone network follows, discussing how it works and the quality requirements that IP must achieve to support voice. Two chapters follow to explain in overview how local and toll switches and integrated services digital network (ISDN) function. Circuit switching has been at the heart of the telephone industry for more than a century and retains stability and service quality that packet technologies cannot yet provide. We devote a chapter to it. Part Two ends with a discussion of softswitches, which are a new generation of IP switches that serve advanced IP networks.

Part Three covers transmission equipment. Separate chapters discuss the fundamental technologies of fiber optics, microwave radio, satellite transmission, cellular and PCS radio systems, wireless, and video. Fiber lies at the heart of the telecommunications infrastructure and is arguably the most important development in the industry’s history. It displaced long-haul microwave, but that technology is becoming more important than ever with an emphasis on communications mobility. Customer demand is fueling a host of new wireless services and protocols that operate in the microwave bands and are receiving a great deal of attention. Video is also becoming a vital Internet access service, and more. The new hybrid fiber-coaxial cable architecture enables cable to compete with the conventional telephone system.

Part Four discusses customer premise equipment. As with the public telephone network, customer premise switching is evolving to IP. We begin this part with a discussion of station equipment, followed by a chapter that discusses features that customer premise switching equipment supports. Chapters follow on conventional digital switching and the newer IP switching. We next discuss automatic media distribution systems, which are evolving from the older automatic call distribution systems. These respond to customer demands for contact alternatives besides the telephone. Other chapters discuss voice processing, electronic messaging, and facsimile.

Part Five pulls together the building blocks we have discussed in the earlier chapters into completed and functioning telecommunications networks. This part illustrates the tremendous variety of alternatives that are available and discusses how and where they are applied. We begin this part with the discussion of enterprise networks, which is a blanket term covering the networks organizations use to link the enterprise. Following that, other chapters cover metropolitan area networks, wide area data networks, frame relay, asynchronous transfer mode, and IP data networks. The IP chapter discusses multi-protocol label switching (MPLS), which is evolving into a platform for handling multimedia applications over IP networks. We discuss testing and network management systems and how they are evolving to enable humans to cope with the increasing complexity of modern networks. The final chapter in the book looks ahead a few years with a view of where telecommunications technology is headed.