CHAPTER 1 INTRODUCTION TO MICROCOMPUTERS This paper identifies the current state-of-the-art microcomputer system design. It begins by giving insights into the introduction, evolution and trends in the microcomputer design in order to get a proper overall understanding. The various system factors of architectural design, process technology, increasing system complexity, and pricing are considered. A microcomputer is a digital computer whose central processing unit consists of a microprocessor, a single semiconductor integrated circuit chip. Microcomputers are the driving technology behind the growth of personal computers and workstations. The capabilities of today's microprocessors in combination with reduced power consumption have created a new category of microcomputers: hand-held devices. Some of these devices are actually general-purpose microcomputers: They have a liquid-crystal-display (LCD) screen and use an operating system that runs several general-purpose applications. Many others serve a fixed purpose, such as telephones that provide a display for receiving text-based pager messages and automobile navigation systems that use satellite-positioning signals to plot the vehicle's position. The microprocessor acts as the microcomputer's central processing unit (CPU), performing all the operations necessary to execute a program. The various subsystems are controlled by the central processing unit. Some designs combine the memory bus and bus input/output into a single system bus. The graphics subsystem may contain optional graphics acceleration hardware. A memory subsystem uses semiconductor random-access memory (RAM) for the temporary storage of data or programs. The memory subsystem may also have a small secondary memory cache that improves the system's performance by storing frequently used data objects or sections of program code in special high-speed RAM. The graphics subsystem consists of hardware that displays information on a color monitor or LCD screen: a graphics memory buffer stores the images shown on the screen, digital-to-analog convertors (DACs) generate the signals to create an image on an analog monitor, and possibly special hardware accelerates the drawing of two- or three-dimensional graphics. (Since LCD screens are digital devices, the graphics subsystem sends data to the screen directly rather than through the DACs.). The storage subsystem uses an internal hard drive or removable media for the persistent storage of data. The communications subsystem consists of a high-speed modem or the electronics necessary to connect the computer to a network. Microcomputer software is the logic that makes microcomputers useful. Software consists of programs, which are sets of instructions that direct the microcomputer through a sequence of tasks. A startup program in the microcomputer's ROM initializes all of the devices, loads the operating system software, and starts it. All microcomputers use an operating system that provides basic services such as input, simple file operations, and the starting or termination of programs. While the operating system used to be one of the major distinctions between personal computers and workstations, today's personal computer operating systems also offer advanced services such as multitasking, networking, and virtual memory. All microcomputers exploit the use of bit-mapped graphics displays to support windowing operating systems.CHAPTER 2 FASTER, SMALLER, CHEAPER: EVOLUTION OF MICROCOMPUTERS A microcomputer is a computer built around a single-chip microprocessor. Less powerful than minicomputers and mainframes, microcomputers have nevertheless evolved into very powerful machines capable of complex tasks. Technology has progressed so quickly that state-of-the-art microcomputers are as powerful as mainframe computers of only a few years ago, at a fraction of the cost. Amajorsteptowardthe modern microcomputers (PC as it may be called today) came in the 1960s when a group of researchers at the Stanford Research Institute (SRI) in California began to explore ways for people to interact more easily with computers. The SRI team developed the first computer mouse and other innovations that would be refined and improved in the 1970s by researchers at the Xerox PARC (Palo Alto Research Center, Inc). The PARC team developed an experimental PC design in 1973 called Alto, which was the first computer to have a graphical user interface (GUI). Twocrucialhardwaredevelopments would help make the SRI vision of computers practical. The miniaturization of electronic circuitry as microelectronics and the invention of integrated circuits and microprocessors enabled computer makers to combine the essential elements of a computer onto tiny silicon computer chips, thereby increasing computer performance and decreasing cost. BecauseaCPUcalculates, performs logical operations, contains operating instructions, and manages data flows, the potential existed for developing a separate system that could function as a complete microcomputer. The first such desktop-size system specifically designed for personal use appeared in 1974; it was offered by Micro Instrumentation Telemetry Systems (MITS). The owners of the system were then encouraged by the editor of Popular Electronics magazine to create and sell a mail-order computer kit through the magazine. TheAltair 8800isconsidered to be the first commercial PC. The Altair was built from a kit and programmed by using switches. Information from the computer was displayed by light-emitting diodes on the front panel of the machine. The Altair appeared on the cover of Popular Electronics magazine in January 1975 and inspired many computer enthusiasts who would later establish companies to produce computer hardware and software. Thedemandforthemicrocomputer kit was immediate, unexpected, and totally overwhelming. Scores of small entrepreneurial companies responded to this demand by producing computers for the new market. The first major electronics firm to manufacture and sell personal computers, Tandy Corporation (Radio Shack), introduced its model in 1977. It quickly dominated the field, because of the combination of two attractive features: a keyboard and a display terminal using a cathode-ray tube (CRT). It was also popular because it could be programmed and the user was able to store information by means of cassette tape. Americancomputerdesigners Steven Jobs and Stephen Wozniak created the Apple II in 1977. The Apple II was one of the first PCs to incorporate a color video display and a keyboard that made the computer easy to use. Jobs and Wozniak incorporated Apple Computer Inc. the same year. Some of the new features they introduced into their own microcomputers were expanded memory, inexpensive disk-drive programs and data storage, and color graphics. Apple Computer went on to become the fastest-growing company in U.S. business history. Its rapid growth inspired a large number of similar microcomputer manufacturers to enter the field. Before the end of the decade, the market for personal computers had become clearly defined.In1981IBMintroduced its own microcomputer model, the IBM PC. Although it did not make use of the most recent computer technology, the IBM PC was a milestone in this burgeoning field. It proved that the PC industry was more than a current fad, and that the PC was in fact a necessary tool for the business community. The PCs use of a 16-bit microprocessor initiated the development of faster and more powerful microcomputers, and its use of an operating system that was available to all other computer makers led to what was effectively a standardization of the industry. The design of the IBM PC and its clones soon became the PC standard, and an operating system developed by Microsoft Corporation became the dominant software running PCs. Agraphical user interface (GUI)a visually appealing way to represent computer commands and data on the screenwas first developed in 1983 when Apple introduced the Lisa, but the new user interface did not gain widespread notice until 1984 with the introduction of the Apple Macintosh. The Macintosh GUI combined icons (pictures that represent files or programs) with windows (boxes that each contain an open file or program). A pointing device known as a mouse controlled information on the screen. Inspired by earlier work of computer scientists at Xerox Corporation, the Macintosh user interface made computers easy and fun to use and eliminated the need to type in complex commands.Beginningintheearly 1970s, computing power doubled about every 18 months due to the creation of faster microprocessors, the incorporation of multiple microprocessor designs, and the development of new storage technologies. A powerful 32-bit computer capable of running advanced multiuser operating systems at high speeds appeared in the mid-1980s. This type of PC blurred the distinction between microcomputers and minicomputers, placing enough computing power on an office desktop to serve all small businesses and most medium-size businesses. Duringthe1990stheprice of personal computers came down at the same time that computer chips became more powerful. The most important innovations, however, occurred with the PC operating system software. Apples Macintosh computer had been the first to provide a graphical user interface, but the computers remained relatively expensive. Microsoft Corporations Windows software came preinstalled on IBM PCs and clones, which were generally less expensive than Macintosh. Microsoft also designed its software to allow individual computers to easily communicate and share files through networks in an office environment. The introduction of the Windows operating systems, which had GUI systems similar to Apples, helped make Microsoft the dominant provider of PC software for business and home use. PCsintheformofportable notebook computers also emerged in the 1990s. These PCs could be carried in a briefcase or backpack and could be powered with a battery or plugged in. The first portable computers had been introduced at the end of the 1980s. The true laptop computers came in the early 1990s with Apples Powerbook and IBMs ThinkPad. PCscontinuetoimprove in power and versatility. The growing use of 64-bit processors and higher-speed chips in PCs in combination with broadband access to the Internet greatly enhances media such as motion pictures and video, as well as games and interactive features. The increasing use of computers to view and access media may be a further step toward the merger of television and computer technology that has been predicted by some experts since the 1990s. In 2012, the Raspberry Pi credit-card-sized single-board computer was launched, directly inspired by Acorn's BBC Micro of 1981, and including support for BBC BASIC. A second revolution in computing is beginning with Raspberry Pi.

CHAPTER 3TRENDS IN MICROCOMPUTER SYSTEM DESIGN Early microcomputer designs placed most of their emphasis on CPU considerations and gave input/output considerations a much lower priority. Early device designers were not systems oriented and, as a result, applied most of their efforts to developing a CPU along the lines of a minicomputer type of architecture. Fortunately, these designs were general enough so that they could be used in many applications, but they were certainly not an optimum design for the types of jobs people want to do with microcomputers. As these first microcomputers were applied to specific products, the importance to I/O capability became apparent because of the nature of the problems being solved. Data was being sensed and input, limited computations were being made, and the transformed data was being output. In most cases, the application was a real time control function with many inputs and outputs such as in a printer controller or a cash register. We soon learned a fact that the big computer systems people had known all along. This was that the CPU is just a small, albeit an important, element of an overall computer system; furthermore, the I/O subsystems may be higher in dollar content than the mainframe and can affect system throughput just as much, if not more, than the CPU. As a result, a series of programmable parallel and serial I/O devices were soon developed by some major microcomputer vendors. These programmable I/O devices could be configured for various input/output configurations by means of control words loaded by the CPU; they also performed all data transfer handshaking protocol. Some vendors, Rockwell being the leader in this particular area, went a step further and developed peripheral controllers such as keyboard/display controllers and various low speed printer controllers which were functionally independent of the CPU. The CPU controls the transfer of data and status information to and from these peripheral controllers; the controllers then perform all detailed peripheral control functions independent of the CPU. This permits the CPU to operate in a system executive mode; the tasks were set up and monitored by the CPU, but the CPU was free to execute other tasks while the detailed task was being executed by the peripheral controller device. Thus, the use of distributed processing design techniques in microcomputer systems began and offered substantial benefits for the user over the CPU oriented approach. First, the MOS/LSI peripheral controller represented a significant cost advantage over peripheral controllers implemented with discrete logic. The same benefits of MOS/LSI derived in CPU implementations also apply to peripheral controllers, i.e., low cost, low power, and functional size reductions. Second, the intelligent peripheral controller overcame the inherent disadvantage of MOS/LSI, that of lower speed operation compared to equivalent discrete logic implementations, by providing parallelism in executing system functions. Thirdly, the use of intelligent peripheral and I/O controllers significantly reduced the software complexity of real time operations. The simultaneous real time control of several system functions by the CPU can result in very complex software and greatly complicate the addition of future system functions. In CPU oriented systems, a law of nature working against you is that as the percentage utilization factor of the CPU gets above 60 to 70 percent, the software complexity for real time functions tends to go up in some exponential manner. In microcomputers, it is extremely important to minimize software complexity since a large majority of people writing software for them are converted logic designers, not professional programmers. The software required to support an intelligent MOS/LSI printer controller, for example, consists of a simple 5 to 6 instruction loop transferring data to be printed to that device. In these cases, we are essentially using dedicated MOS/LSI logic to replace complex software. The next logical step beyond intelligent controllers in the distributed processing trend in microcomputers is the use of multiple microprocessors in the same system. In this approach, multiple CPU's are used to perform various sub assignments in the overall system design. Much effort has been expended by computer system designers to solve the general multiprocessor problems of programming and real time task allocation; this is, of course, a very difficult problem which requires much additional effort. In the microcomputer applications, however, the system is designed and dedicated to a fixed set of tasks. The specific, dedicated tasks are easily assigned and coded independently, to a large degree; a solution to the generalized problem is not required in these specific cases. The multi-processor approach offers a significant increase in performance over a single microprocessor, and additionally simplifies overall software requirements since the multiple CPU's are not loaded nearly as heavily as a single CPUwould be in performing the total job. Another aspect of distributing intelligence throughout the microcomputer system is the integration of interrupt and DMAhandling techniques into the CPU and various I/O and peripheral controller devices. Again, methods of dispersing the workload outside of the CPU help prevent CPU bottlenecks and their attendant problems. In this philosophy, interrupts become self-identifying requiring no polling and interrupt requests may be generated by any device and each device has its own built-in method of prioritization. In this concept, DMA requests and terminations can also be generated by I/O and peripheral devices.Because of the low cost attributes of MOS/LSI, the use of DMA techniques.should be carefully re-evaluated. Previously, DMA has been associated only with high speed data transfers; it has been an expensive option in minicomputers which has limited its philosophy of usage. Now, in a microcomputer, it is so inexpensive that it canbe considered simply as a means of reducing system overhead and software complexity. A sizeable simplification of system software and reduction in CPU overhead can be achieved even in very slow data transfer situations. Instruction sets on initial microcomputers were pretty much a scaled down, basic copy of classical minicomputer instruction sets. As device functional densities increased, instruction setsgrew under the influence of two forces. The first force is to add additional traditional minicomputer instructions; the second force is to add instructions which more uniquely address specific requirements for microcomputer types of applications. Typical of theseare bit manipulation instructions, block move instructions, and additional addressing modes for all instructions. Bit manipulation instructions become very important in microcomputers because of the heavy I/O control aspects of most applications. The useof memory mapped I/O ports with bit set, reset, and bit test instructions provide a new advance in bit oriented I/O control applications. Similarly, bit rotation instructions can beutilized to effectively scan multiple output lines. One trend in instruction sets is to remove the instruction "action" from the CPU registers to memory locations or I/O locations, at least from the programmers point of view. These macro type instructions represent a first step in utilizing more complex control logic to obtain, in some degree, the effect of a higher level programming language. The major challenge of system architects is to judiciously combine and integrate hardware and software techniques to reduce by an order of magnitude the initial effort required to program a microcomputer application.3.1 MICROPROCESSOR DESIGN The CPU is a very important element of an overall computer system. A processor is at the heart of every computer system that we build today. Around this processor, you find several other components that make up a computer. Memory for instruction and data storage and input-output devices to communicate with the rest of the world, like disk controllers, graphics cards, keyboard interfaces, network adapters, etc. The purpose of the processor is to execute machine instructions. Thus, the logical operation of a processor is defined by the instruction set architecture (ISA) that it executes. Multiple different processors can implement the same ISA. What differentiates such processors is their processor architecture, which is the way that each processor is organized internally in order to achieve the goal of implementing its ISA. In the past thirty years, computer technology advances have fundamentally changed the practice of business and personal computing. During these three decades, the wide acceptance of personal computers and the explosive growth in the performance, capability, and reliability of computers have fostered a new era of computing. The driving forces behind this new computing revolution are due primarily to rapid advances in computer architecture and semiconductor technologies. This section will examine key architectural and process technology trends that affect microprocessor designs. Microprocessor Evolution In 1965 Gordon Moore observed that the total number of devices on a chip doubled every 12 months at no additional cost. He predicted that the trend would continuein the 1970s but would slow after 1975. Known widely as the Moores Law, these observations made the case for continued wafer and die size growth, defect densityreduction, and increased transistor density as technology scaled and manufacturing matured. Transistor count in leading microprocessors has doubled in each technology node, appropriately every 18 to 24 months. Factors that drove up transistor count areincreasingly complex processing cores, integration of multiple levels of caches, and inclusion of system functions. Microprocessors frequency has doubled in each generation, results of 25% reduction of gates per clock, faster transistors and advanced circuit design. Die size has increased at 7% per year while feature size reduced by 30% every 2 to 3 years. Together, these fuel the transistor density growth as predicted by Moores Law. Die size is limited by the reticle size, power dissipation, and yield. Leading microprocessors typically have large die sizes that are reduced with more advanced process technology toimprove frequency and yield. As feature size gets smaller, longer pipelines enable frequency scaling, this has been a key driver for performance.

Transistor Scaling Device physics poses several challenges to future scaling of the bulk MOSFET structure. Leakage through the gate oxide by direct band-to-band tunneling limitsphysical oxide thickness scaling and will drive high-k gate material adoption. Sub-threshold leakage current will continue to increase. Researchers have demonstratedexperimental devices with a gate length of only 15nm,which will enable chips with more than one billion transistors by the second half of this decade. While bulk CMOS transistor scaling is expected to continue, novel transistor structures are being explored.

Interconnect Scaling As advances in lithography decrease feature size and transistor delay, on-chip interconnect increasingly becomes the bottleneck in microprocessor designs.Narrower metal lines and spacing resulting from process scaling increase interconnect delay. Local interconnects scale proportionally to feature size. Global interconnects, primarily dominated by RC delay, are not only insufficient to keep up but are rapidly worsening. Repeaters can be added to mitigate the delay but consume power and die area. Low resistivity copper metallization and low-k materials such as fluorine-doped SiO2 (FSG) are employed to reduce the worsening interconnect scalability. In the long term, radically different on-chip interconnect topology is needed to sustain the transistor density and performance growth rates as in the last three decades.

Packaging The microprocessor package is changing from its traditional role of protective mechanical enclosure to a sophisticated thermal and electrical management platform.Recent advances in microprocessor packaging include the migration from wirebond to flip-chip and from ceramic to organic package substrates. Looking forward, emergingpackage technologies include the bumpless build-up layer (BBUL) packages, which are built around the silicon die. The BBUL package provides the advantages of smallelectrical loop inductance and reduced thermo mechanical stresses on the die interconnect system using low dielectric constant (low-k ) materials. This packagingtechnology allows for high pin count and easy integration of multiple electronic and optical components.

Power Dissipation Power dissipation increasingly limits microprocessor performance. The power budget for a microprocessor is becoming a design constraint, similar to the die area and target frequency. Supply voltage continues to scale down with every new process generation, but at a lower rate that does not keep up with the increase in the clock frequencyand transistor count. Power increases with frequency for two processor architectures and the last two process generations. Architectural techniques like on-die power management, and circuit methods such as clock gating and domino to static conversion, are employed to control the power increase of future microprocessors.

Clock Speed Microprocessor clock speed increases with faster transistors and longer pipelines. Frequency scales with process improvements for several generations of Intel microprocessors with different microarchitectures. Holding process technology constant, as the number of pipeline stages increase from 5 to 10 to 20 from the original Intel Pentium through the Pentium 4, clock speeds are significantly increased. Frequency increases have translated into higher application performance. Additional transistors are used to reduce the negative performance impact of long pipelines; an example is increasingly sophisticated branch predictors. Process improvements also increase clock speed in each processor family with similar number of pipe stages. Later designs in a processor family usually gain a smaller frequency advantage from process improvements because many micro -architectural and circuit tunings have been realized in earlier designs. Some of the later microprocessors are also targeted to a power-constrained environment that limits their frequency gain.

Cache Memory Microprocessor clock speeds and performance demands have increased over the years. Unfortunately, external memory bandwidth and latency have not kept pace. This widening processor-to-memory gap has led to increased cache sizes and increased number of cache levels between the processing core(s) and main memory. As frequency increases, first level cache size has begun to decrease to maintain low access latency, typically 1 to 2 clocks. As aggregate cache sizes increase in symmetric multiprocessor systems (SMP), the ratio of conflict, capacity, and coherency misses, or cache-to-cache transfers, will change. Set associative caches will see reduction in conflict and capacity misses relative to cachesize increases. However, these increases will have smaller impact on coherency misses in large SMP systems. This motivates system designers to optimize for cache-to-cachetransfers over memory-to-cache transfers. Two approaches to achieve this are hyper-threading, also known as multithreading, and chip multiprocessing (CMP).

Input/Output Performance increases lead to higher demand for sustainable bandwidth between a microprocessor and external main memory and I/Os. This has led to faster andwider external buses . High-speed point-to-point interconnects is replacing shared buses to satisfy increasing bandwidth requirements. Distributed interconnects will provide a more scalable path to increase external bandwidth when practical limit of a pin is reached.

CHAPTER 4FEATURES OF TODAYS MICROCOMPUTERS. Todays microcomputers address the challenge of high bandwidth and the need for state-of- the-art computational performance. They are faster, smaller and affordable. The current state of the art microcomputer system designs have the following features common amongst them: Modular Architecture To support the creation of a wide range of implementations the architecture supports modular implementations. A basic implementation might comprise a single processor unit with four functional units. By replicating those design elements, an implementation can be built that includes a few or even hundreds of processors, each with four functional units, each of which can operate on many data items simultaneously with parallel-operation (SIMD) instructions. Conversely, a tiny application specific implementation can be derived from the basic one by trimming the complement of functional units down to one or two and/or removing hardware support for any instructions not needed in its target application. Software Portability The architecture is designed to efficiently execute code generated by installation-time or just-in-time (JIT) compilation techniques. This allows implementations to evolve over time without accumulating the baggage required to support old binaries, as traditional architectures have always done. Instead, software portability across implementations is obtained through use of architecture-neutral means of software distribution. Multiple Levels of Parallelism The architecture provides the ability to exploit parallelism at many levels - at the data word level through SIMD instructions, at the instruction level through multiple functional units per processor, at the thread-of-execution level through support for multithreaded software, and at the system level through its intrinsic support for "MPs-on-a-chip" (multiple processor units per implementation). An implementation with more than one functional unit per processor unit provides MSIMD: multiple single instructionmultiple-data parallelism. Multiple Processor Units per Cluster Although an implementation can be a single processor unit, many architectures today explicitly incorporates the concept of multiple processors per implementation. Given 21st century semiconductor density, each such array of processor units or processor cluster" can be implemented on a single chip. As semiconductor technology advances, clusters with more processors per chip can be implemented. Multiple Functional Units per Processor Unit Processor unit can issue multiple instructions simultaneously, one to each of its functional units. Most implementations are expected to provide two to four functional units per processor unit. Multithreaded SoftwareExecution of multithreaded software comes naturally given the architecture's ability to execute multiple threads simultaneously on multiple processor units.

SIMD Instructions At the lowest level of parallelism, several architectures provide SIMD (Single Instruction/ Multiple Data) or "vector" instructions. A SIMD instruction executing in a single functional unit could perform the same operation on multiple data items simultaneously. Integral Support for Media-Rich Data The architecture is particularly well-suited for processing media-rich content because it directly supports common media data types and can process multiple simultaneous operations on that data. Processing power is multiplied on three levels: Single Instruction/Multiple Data (SIMD) DSP-like instructions in each functional unit, multiple functional units per processor unit, and multiple processor units per processor cluster. Balanced Performance: Processor versus Memory and I/O The microcomputer implementation is designed to utilize several techniques to balance processor speed with access to external memory and I/O devices:100's of general-purpose registers per processor unit, which reduce the frequency of memory accesses Load-Group instructions, which increase bandwidth into the processor by simultaneously loading multiple registers from memory or an I/O device Store buffering, which increases bandwidth out of the processor by optimizing Store operations initiated by software.

Data Type-Independent Registers The general-purpose register file in some microcomputer implementation is data type-agnostic: any register can hold information of any data type and be accessed by any instruction. In particular, there is no distinction between integer and floating-point registers. This allows registers to be allocated as needed by each application, without restrictions imposed by hardware partitioning of the register set. Instruction Grouping Grouping instructions across multiple functional units can be performed dynamically in hardware (as in a superscalar processor), statically by a compiler, or by some combination of the two. Rather than devoting valuable chip area to hardware grouping Logic. Data and Address Size Implementation may implement either 32- or 64-bit addressing and data operations, as dictated by the needs of its target applications. Context Switch Optimization Process (task) context switch time can be reduced by using the architecture's "register dirty bits", which allow an operating system to minimize the number of registers saved and restored during a context switch.

4.1 AN OVERVIEW OF TODAYS SINGLE-BOARD MICROCOMPUTERS There are quite a few single-board microcomputers out there today to choose from. Some of them offer better performance and more memory than others; some of them have a great variety of connectors while others only have the necessary minimum. A part of these devices can connect to custom hardware through general purpose input-output pins, while others are more integrated and less customizable. Most of them are based on the ARM architecture, which restricts their use to operating systems like Linux, Android, etc., but a few surprise us with an x86 design and can even run Windows. Although they are generally small, there still are significant differences between them in size. Some of them target home users while others are built for hackers and computer experts. And last, but not least, the price of these micro computers can differ a lot. These microcomputers include: Olimex A13 OLinuXino, ODROID-X2, BeagleBone, Cubieboard, Gooseberry Board, Hackberry Board, FOXG20, etc. Our focus will be on Raspberry Pi which is undoubtedly the most famous single-board micro PC. Raspberry Pi Designed and marketed by the non-profit Raspberry Pi Foundation, manufactured by Sony UK and sold by Farnell / Element14, the Raspberry Pi is, without a doubt, the most famous small computer (single-board micro PC) today. Its creation revolves around a noble cause, The Raspberry Pi Foundation aims to give the world, especially children, a very cheap computer which they can use to learn programming and to put their creativity to work in general. Released in early 2012, the Raspberry Pi combines some very appealing hardware characteristics, like fairly good performance (the 700 Mhz ARM CPU can be overclocked to 1GHz; 256 MB memory for model A and 512 MB memory for model B), extremely low power consumption (1.5 W max for model A and 3.5 W max for model B), which makes it suitable for battery-powered independent projects, and custom connectivity to special hardware through programmable GPIO pins. Combine all this with a very low price (25$ for model A and 35$ for model B) and a large, helping community and you definitely have a winner if you want to choose a fairly good small computer which can run Linux for example (or Android, RISC OS, etc.) and which needs to run all kinds of applications that dont need a lot of resources (for home use, for a small server or as part of a custom hardware system). It is probably the best choice also in case you want to take the easy road into the world of microcomputers because of its popularity, which translates to a huge number of Raspberry Pi owners who can and will probably help you with any questions or problems that you may encounter.Specifications: CPU: ARM1176JZF-S 700 MHz processor GPU: VideoCore IV, capable of BlueRay quality playback, with OpenGL ES 2.0 RAM: 256 MB (model A) or 512 MB (model B) Connectors: USB, HDMI, Composite RCA, 3.5 mm audio jack, 10/100 Ethernet, micro USB power cord Storage: SD/MMC/SDIO card

Chapter 5CONCLUSION In this paper, I have presented an overview of the past developments and current state of the art of microcomputers and microcomputer system design. New trends are towards High compute density, Low cost, Power efficiency and High system reliability. From Intel 4004 of 1971, which has 1 core, no cache, and 23K transistors, to Intel 8008, of 1978, with 1 core, no cache, 29K, transistors; and Intel Nehalem-EX, 2009, which has 8 cores, 24MB cache, and 2.3B transistors, we see that theres been a great success in the evolution of microcomputer and its design with focus on arriving at computers that are faster, smaller, affordable and more efficient. The aim of a microcomputer designer is to achieve an architecture thatd result in control of complexity, maximization of performance and minimization of cost; and presently we have small PCs like Raspberry Pi beginning the second evolution of microcomputers after Commodore for the first. Besides the ever increasing transistor count and device speed, future implementationtechnologies also pose significant challenges to the architect to get the highest benefit and best possible performance from the technology advances. The scope and range of microcomputer capabilities broadens every day as software becomes more sophisticated, but are largely dependent upon the data-storage capacity and data access speed of each computer.

REFERENCES1. An overview and comparison of todays single-board microcomputers. (January 2013). Retrieved May 15, 2014, from http://www.iqjar.com/jar/an-overview-and-comparison-of-todays-single-board.2. Ceruzzi: A History of Modern Computing, Second Printing, 1999.3. G. Moore, Cramming more components onto integrated circuits, Electronics, Vol. 38, No. 8, April 19, 1965.4. Goldstine: The Computer: From Pascal to Von Neumann, 2nd printing, 1973.5. Hadi Esmaeilzadeh, Ting Cao, Xi Yang, Stephen M. Blackburn, and Kathryn S. McKinley. Looking back and looking forward: power, performance, and upheaval. CACM 55, 7 (July 2012), 105-114.6. Hennessy & Patterson: Computer Architecture A Quantitative Approach, 2nd ed., 1996.7. McGraw-Hill Science & Technology Encyclopedia: Microcomputer.8. "Microcomputer." Microsoft Encarta 2009 [DVD]. Redmond, WA: Microsoft Corporation, 2008. 9. Shekhar Borkar, Andrew A. Chien, The Future of Microprocessors. Communications of the ACM, Vol. 54 No. 5, Pages 67-77 10.1145/1941487.1941507.10. Standard Performance Evaluation Corporation.(April 2002). Retrieved May 16, 2014, from http://www.spec.org.11. TRENDS IN MICROCOMPUTER TECHNOLOGY J. E. Bass Rockwell International, 1977.17