2/3/2014
Week 4 Assignment 1 Computer Architecture

John von Neumann was a mathematician and polymath who was born on December 28 1903 and while he made major contributions to a number of fields the one we care about in the IT field is von Neumann Architecture. In 1946 he co wrote a paper with Arthur W. Burks and Hermann H. Goldstine and out lined what would be need for a general purpose electronic computer. The title of the paper was “Preliminary Discussion of the Logical Design of an Electronic Computing Instrument” ( von Neumann , 2000) and the idea of the paper would have far reaching impacts on the field of computer science and would lead the design and building of the first computer call Manchester Mark I witch ran its first program in 1948. While the history lesson of the man is all well and good the question we need to ask ourselves is how the von Neumann architecture works and what goes into the process. Von Neumann believe that computing machines contained four parts the arithmetic logic unit this part of the architecture is solely involved with carrying out calculations upon the data such as adding subtracting multiplying and division the control unit will manage the process of moving data and program into and out of the memory and also deal with carrying out program instructions the memory that can hold data and also the program processing that data in modern computers this RAM and the input-output devices which allows for the idea that a person needs to interact with the machine. ( von Neumann , 2000) To John von Neumann the key was to find a way to store data and results of computation but also to have instructions stored as well. (Von Neumann, 2000) Then he defined the control components as that which would run the coded instructions stored in memory. However moving all of the information to various parts of the modern computer is done by the system Bus however since this was not about of the original design let us discuss what a system bus is. The system bus of computers architecture is a subsystem that transfers information from computer components inside a computer. A bus defines its set of connectors to physically plug devices, cards or cables together. About 30 years ago the processors we so slow that the processor and the bus were synchronized and there was only one bus in a machine. As computers got more complicated they broke the system bus down into three parts the Front side bus, Backside Bus and PCI Cards. (Abbott, 2004) The front side bus is the physical connection that links most of the components in the computer this includes RAM, hard drives and PCI slots. The Backside bus is a separate usually works at the same speed as the processor and handles all the caching work as efficiently as possible. In the pass the cache was a separate chip the need a lot of memory but as computers has evolved it was integrated into the main processor. In a lot of system design since the cache is not about of the processor most people don’t think the backside bus counts a system bus anymore. PCI are system buses that can be added or removed as need and connect up to five external components the five connectors of an external component can be replaces for two fixed devices on the motherboard. PCI card use either a 47 pin or 49 pin to connect and can work without CPU intervention. (Abbott, 2004) The PCI bus can work with so few pins because of multiplexing this means that more than a single signal can be sent at one time over a single pin. In 1991 Intel proposed the PCI standard however it didn’t get any real fame until Windows 95 mostly because windows supports a new feature called Plug and Play. A great leap in computer science was the introduction of Boolean or Boolean logic which is a subset of algebra used to create true/false statement. You might ask yourself how this works with programming but since computers use ones and zeros for programming you can use the true and false statements to mean 1 for true and 0 for false. (brown, 2012)In the end you get complex programming by linking strings of Boolean statements together as logic gates. Logic gates are the fundamental building concepts most logic gates use two inputs of binary values. Some circuits can have more than one logic gate such as microprocessors which have millions of them. When you combine millions of logic gates it’s possible to perform highly complex operations. The number of logic gates depends on the size of the microchip involved However how does Boolean logic work well Boolean logic is made or three basic expressions known as AND, OR, NOT and these expression when used correctly return a true or false statement. (brown, 2012)Here are some examples of Boolean expressions. x AND y - returns True if both x and y are true; returns False if either x or y are false. x OR y - returns True if either x or y, or both x and y are true; returns False only if x and y are both false. x XOR y - returns True if only x or y is true; returns False if x and y are both true or both false.
NOT x - returns True if x is false (or null); returns False if x is true. (brown, 2012)
Boolean expressions are also used in working with search engines and other search fields to narrow down choices. When a keyword is enter you refine you search choices using Boolean operators with however not all search engines use the And, OR, Not some use other syntax instead like the plus or minus symbols. (brown, 2012)If you are ever not sure what your search engine uses you should check the help sections for more information. However with these complex operations going on inside the computer you need some place to store the information and that is where memory and data storage comes in. If we take a look at how memory works first this will lead into storages types. Powerful CPUs need quick and ready access to a good deal of data to effectively perform their functions computer design use to try and have enough memory to support the CPU however this soon became cost prohibited so the concept of tiering which is when you take expensive memory in small quantities and back it up with large quantities of less expensive memory. Memory is broken down into a hierarchy starting with the cheapest form of read/write in use today which is the hard disk which provide are large quantity of inexpensive memory. It’s so cheap that CPU’s use a part of the hard disk to make up virtual memory which many browsers make use of. The next stage is RAM which I talk about earlier when I discussed system buses. Its stores information’s for a temporary basis however it has the problem that is losses everything the moment the system is turned off. The next is Read only Memory or ROM which is a type of permanent memory that is added by the manufacturer or the user most time you load the system BOIS onto it and it’s cheaper that RAM. In the later years we have come across new types of stores from compact discs to external hard drive and like internal hard drives they can provide cheap forms of storages for computers however they can be easily affected by viruses. If the last few years we have also seen a another from a cheap and easy memory know as solid state memory which we seen as USB memory.

Von Neumann , J. (2000). The computer and the brain. (2nd ed.). Yale University Press.
Abbott, D. (2004). Pci bus demystified. (2nd ed.). Newnes. brown, F. M. (2012). Boolean reasoning: The logic of boolean equations . (2nd ed.). Dover Publications.