CPS120: Introduction to Computer Science Introduction to Computers

 Objectives –Understand the history of computers –Understand the components that make up a desktop PC –Understand the basics of computer architecture –Understand the role of an operating system –Understand the role of assemblers, interpreters, & compilers

History of Computers  Abacus  Pascal’s gear-driven counting machine –His father was a tax collector  Babbage designed a programmable computer (1834)  Ada Augusta King, Countess of Lovelace, translates Menabrea's pamphlet on the Analytical Engine, adding her own notes, and becomes the world's first programmer.

"Modern" Developments  Hollerith built machine for US census bureau & founded IBM  1946, ENIAC used vacuum tubes (Univ of Penn) - very hot, needed AC, military paid for this researchENIAC  Transistors used in 1950’s, didn’t burn out like vacuum tubes  Integrated circuits (chips) used in 1960’s  Microprocessor used in 1970’s  Supercomputers, mainframes, minicomputers, workstations, desktop computers

System Components  Hardware –I/O devices (input/output) keyboard, mouse, monitor, etc. –CPU –Primary Storage –Secondary Storage  Software

Computer Architecture  Microprocessor (examples Pentium, Pentium II, PowerPC, etc.) –includes Bus Interface Unit, Arithmetic & Logic Unit (ALU), Control Unit, registers –motherboard is simply the main circuit board that contains most of these parts –the CPU (central processing unit) is considered to be most of these parts taken as a whole  Bus –connects the microprocessor to the RAM & ROM –addresses for data and instructions are important

Storage Devices  Primary storage –RAM (Random Access Memory, or just “memory” for short) active data that is being stored, lost if power is cut off so save often –ROM (Read-Only Memory) commands that are permanently stored on chips PC’s use BIOS, Macs use the Toolbox  Secondary storage –Hard disk, floppy disks –Slower method of storage & retrieval but “safer”

Software: Systems Software  Operating systems –Controls the hardware components (disks, CPU, printers, etc.) –Windows XP, Windows NT/2000, Windows 9- X, MS-DOS, OS/2, MacOS, Unix, Linux, BeOS

Software: Application Software  Office products –Word processors –Spread sheets –Presentation software –  Business applications –General ledger –Financials Accounts payable Accounts receivable –HRMS –Fixed assets/inventory

Programming Software  Text Editor – Used by the programmer while coding the program in a programming language Like a word processor - creates a text file containing the program's instructions or "source code" –Examples are “emacs” and “vi” editors in Unix systems –Other editors are NotePad and WordPad which are text- based

Programming Software  Interpreters –Translates source code into machine code line by line  Compiler –Translates source code into an object file, than uses linker to create an executable file A source module (source code) becomes an "object" module (compiled module) Then it is linked with system modules to become a "load" module (linked module)  It is usually more efficient to use a compiler

Data Representation  Objectives –Understand how data & instructions are stored in the PC –Understand the basics of the binary numbering system

Representing Data  Data can be numeric, alphabetic, or alphanumeric  Computer only uses “on” & “off” within its circuits

Representing Data: Bits  Computer only uses “on” & “off” within its circuits  Binary number system –“On”, 1, high state of electricity –“Off”, 0, low state of electricity –Bits (0’s and 1’s)

Representing Data: Bytes  Byte = 8 bits (2 3 )  256 possible combinations of 8 bits  Decimal system is cumbersome & awkward for pc’s –Can convert from decimal to binary & vice versa ASCII (American standard code for information interchange)  128 characters in the 7-bit set

Representing Instructions:  Low Level Languages –Each computer uses its own machine language –Assembly is a low-level language close to machine language Assembly languages are different on each computer An assembler converts a program into machine language