The Evolution of Computers: From Human Calculators to Modern Machines, Dispense di Computer Graphics

Scarica The Evolution of Computers: From Human Calculators to Modern Machines e più Dispense in PDF di Computer Graphics solo su Docsity! Computer skills 2nd semester What defines a computer? It could be a monitor, a keyboard or mouse. However, devices such as smartphones or tablets are considerable computers even if they do not have the previous elements. To define a computer, we need - An information processor (the brain of the computer) which is in charge of elaborating all the necessary info - An input (some data from the external world) and output (the calculation performed by the computer) - An internal storage to keep all the important data to perform all the required calculations Definition of modern computer: inputs, outouts, processes and stores Keyboard, monitor, mouse are not strictly necessary to define a computer (phones, tablets) The first computers were people. The word “computer” was initially used to describe those human beings (usually women) whose job it was to perform the repetitive calculations required to compute such things as navigational tablets or planetary positions. This is also the reason that leaded to find something that could replace this repetitive cycle. - Before the computer was invented, people relied on other things like abacus to be helped in mathematical problems. This object was used in 300 BC by the Babylonians. The abacus is often wrongly attributed to China. In fact, the oldest surviving abacus was used in 300 B.C. by the Babylonians. The abacus is still in use today, principally in the far east. In 1617 John Napier invented Logarithms, which are a kind of technology that allows multiplication to be performed via addition In 1642 Blaise Pascal, at age 19, invented the Pascaline as an aid for his father who was a tax collector. Pascal built 50 of this gear-driven one- function calculator (it could only add) but couldn't sell many because of their exorbitant cost and because they really weren't that accurate (at that time it was not possible to fabricate gears with the required precision). Jacques de Vaucanson French artist and inventor 1727-1743 – Created a series of mechanical automations that simulated life Best remembered is the “Digesting Duck”, which had over 400 parts. Also worked to automate looms, creating the first automated loom in 1745 Charles Babbage (1791-1871) was an English mathematician who can be considered the father of the programmable computer. He started the project for something called “difference engine” that could calculate values of polynomial functions. It would have used punch-cards and it would have included features such as sequential control and loops. Augusta Ada Bryon King, Countess of Lovelace (1815-1852) came up with the idea of loop: a sequence of instructions in a program which loops endlessly allowing the program to return to a given instruction. The idea is that while we are working using a specific program with our computer, this implies that the program itself has a sequence of instructions that are continuously going on ensuring the correct functioning of the entire problem. This is a way of self-control for the program itself. US census There are some historical examples which have had consequences on the study and development of computers, such as war, the greatest example that we can search for or political events, such as census. According to the US constitution, every 10 years US citizens need to underwear census but according to the great grown in the number of the population, politicians were required to search for an automatic machine that helped them during the next census. - The Hollerith desk consisted in a card reader which sensed the holes in the cars which helped the politicians calculating the census. Hollerith’s company grew up and became the well-known today IBS - By using punch cards, Hollerith created a way to store and retrieve information (not in the inside of the computer, but inside the punch card itself). It was the first type of read and write technology. Some of the biggest advances that led to the modern computer are: electricity, transistor, microchip and data storage. - Alan Mathison Turig was the first one who came up with the idea that computers should be able to resemble the human brain work in order to eventually replace it. He thought that such machines could overcome human intelligence. - During WW2, he used his mathematical skills to decipher the codes the Germans were using to communicate. This was a difficult task because the Germans had developed a type of computer called the Enigma: This device was able to constantly generate changing codes that were impossible for the code breakers to decipher in a timely fashion. - According to him, the Turig machine was able to learn and to be instructed in order to perform a variety of actions. - Computers build on the Turig universal machine store data in their memory, this meant that the entire programs were able to be stored inside the computer (Neumann, around 1944-1945). This concept was revolutionary for the time. Most computers in the 1950’s were designed for a particular purpose. What Turig envisioned was a machine that could do anything, something that we take for granted today. The method of instructing the computer was very important in Turig’s computer. He essentially described a machine which knew a few simple instructions. Making the computer perform a particular task was simply a matter of breaking the job down into a series of these simple instructions, this is identical to the process programmers go through today. Thanks to his ideas and research, it was created the field of artificial intelligence. He believed that almost nothing the brain could do that a well-designed computer could not. Task Processing DOS is Single Process, UNIX supports multi-processing, multiple processes per user, and job control from the shell Command-Line Interface DOS has its command interpreter (command.com). UNIX has the shell (C-shell, Korn Shell, Bourne Shell etc.) Security Some versions of DOS allow password protection on file. UNIX has username/password for logins, and user/group/world permissions on files and directories. Portability DOS runs on Intel processors and compatible devices. UNIX is available for a very wide variety of hardware platforms. Shell-Level Programming DOS has batch files. UNIX has shell scripts. 
 (batch and shell are series of commands) An OS is a program which acts as an interface between computer system users and the computer hardware. It provides a user-friendly environment in which a user may easily develop and execute programs. Otherwise, hardware knowledge would be mandatory for computer programming. OS hides the complexity of hardware. In general, a computer system has some resources which may be utilized to solve a problem. They are Memory Processor(s) I/O File System MOORE’S LAW Moore’s law states that the number of transistors on a microprocessor chip will double every two years or so — which has generally meant that the chip’s performance will, too. For the past five decades, the number of transistors per microprocessor chip — a measure of processing power — has doubled about every two years. Chips also increased their ‘clock speed’, or rate of executing instructions, until 2004, when speeds reached the limit heat. As computers increase in power and shrink in size, a new class of machines has emerged roughly every ten years. The OS manages these resources and allocates them to specific programs and users. An OS provides services for: Processor Management, Memory Management, File Management Os can be used as a predefined library for hardware-software interaction. This is why, system programs apply to the installed OS and they cannot reach hardware directly. Since we have an already written library, namely the OS, to add two numbers we simply write the following line to our program: c = a + b; In an OS installed machine, since we have an intermediate layer, our programs obtain advantage by not dealing with hardware. With the advantage of easier programming provided by the OS, the hardware, the machine language and the OS constitutes a new combination called as a virtual (extended) machine. in fact, OS itself is a program. But it has a priority which application programs don’t have. OS uses the kernel mode of the microprocessor, whereas other programs use the user mode. The difference between two is that; all hardware instructions are valid in kernel mode, where some of them cannot be used in the user mode. A processor has two different modes: user mode and kernel mode. The processor switches between the two modes depending on what type of code is running on the processor. Applications run in user mode, and core operating system components run in kernel mode. In a user-mode application, the OS creates a process for the application. The process provides the application with a private virtual address space. Because an application's virtual address space is private, one application cannot alter data that belongs to another application. Each application runs in isolation, and if an application crashes, the crash is limited to that one application. Other applications and the operating system are not affected by the crash. Limiting the virtual address space of a user-mode application prevents the application from altering, and possibly damaging, critical operating system data. All code that runs in kernel mode shares a single virtual address space. This means that a kernel-mode driver is not isolated from other drivers and the operating system itself. If a kernel-mode driver accidentally writes to the wrong virtual address, data that belongs to the operating system or another driver could be compromised. If a kernel-mode driver crashes, the entire operating system crashes