1. Overview of Computer Systems. Computers are classified based on their generation and type. The architecture of different generations of computers differ with advancement in technology. Changes in computer equipment have gone through four generations namely: - PowerPoint PPT Presentation
Second Generation Computers (1955-1965): Basic electronic components became transistors. Prog-ramming in High level language with punched cards.
Third Generation Computers (1965-1980): Basic technology became integrated circuit (I Cs) allowing many transistors on a silicon chip. Faster, cheaper and smaller in size, e.g., IBM system 360.
Fourth Generation (1980-1990): Personal Computers came to use. Technology in use is large scale integration(LSI). Support for network and GUI.
Computers belong to one of these types based on their size, processing power, number of concurrent users supported and their cost.
• Microcomputers - support only a single user, very compact in size. Processing power is increasing but still limited when shared by many programs and users, e.g., IBM PC, laptops.
• Mini Computers - More processing power can be shared among multiple users, e.g., SGI and SUN workstations. Generally, more expensive than micros
Bits of data are stored in memory and bit collections of size 8 make 1 byte.
A memory cell is made up of 1 to 4 bytes (ie. 8 bits to 32 bits) depending on the word length of the system.
1 kilobyte memory has 1024 bytes (103 or 210) 1 Megabyte memory has 106 or 220 bytes. 1 Gigabyte memory has 109 or 230 bytes. Individual cells in a machine’s main memory are identified with
unique names called addresses The addresses of 1M memory are 0 through 1048575 if a memory
Each cell of memory can be read or written (modified) individually.
RAM is volatile because information stored is lost on power off
Thus, secondary memories are used to store data for future use (disks, CD-ROMs and tapes).
At the user and program level, physical storage addresses are commonly referenced using logical names or addresses like file names for block of data on disk, and variable names for memory cells.
While numeric data are represented in binary, characters are represented using standard codes
One code is ASCII (American standard code for Information Interchange) which uses seven bits to represent a character.
Disks are a common storage device for storing information for future use. Storage space is generally more available on disk which are cheaper per unit of storage space than main memory.
• (3) Network Software for allowing more than one computer to be connected together and to share information (e.g., telnet, ftp).
• (4) Productivity Tools for allowing users to perform daily business and office operations in a more productive fashion called productivity tools (e.g., word processors, database and spreadsheet programs)
• (5) Others, e.g., utility applications like virus checkers.
Before a program written in a high level language is executed by the CPU, it needs to be translated, linked and loaded into memory in a process called compilation and linking.
Program preparation process is:
• Step 1. Type Source program in high level language
• Step 2. Compile to get object program in machine language.
A C source program file must be given a name with .c extension, e.g., test.c and this file must be prepared with a text editor like Unix vi editor, nedit, pico or PC’s notepagd or Turbo C++ Lite editor.
A C compiler is used to compile a C program. To compile on Unix, use: cc filename.c
Program instructions that violate the syntax of grammar rules of C will cause syntax errors and must be corrected before a successful compilation is achieved
Example 2.1: Management wants to see the patterns in absenteeism across its two departments, dept1 and dept2 for one week. It is interested in knowing the total absenteeism in each department in the one week it collected data. You are required to identify the input and output data of this problem and attempt to define an algorithm and a program.
