Operating system, Windows, Internet, HTML notes

An operating system (OS) is system software that manages the computer’s hardware and gives the user and the application programs a way to use that hardware. It is the first program that becomes useful after the firmware (BIOS) has started the machine. Without an OS, Anil would have to talk to the disk, the keyboard and the printer in machine language for every job. With an OS he clicks a folder, types in a word processor, and the OS fetches bytes, shares the CPU, and sends the page to the printer.

Need. The OS is a resource manager. It loads and runs programs (process management). It allots RAM and keeps one program from overwriting another (memory management). It keeps files on disk in named folders (file management). It talks to keyboard, mouse, monitor, printer (device / I/O management). It offers a user interface — CUI (character, as in MS-DOS: you type commands) or GUI (graphical: icons and a pointer). It can also check who may open a file (security). Application software does not drive the hardware directly; it asks the OS.

The four types named in this unit are batch, single user, multiprocessing and time sharing.

Batch. Jobs are collected into a batch and run one after another with little or no conversation with the user while they run. The user prepares a job (punched cards in older labs; a file of commands later), submits it, and collects the output later. Second-generation rooms worked this way. There is no sitting at the screen to correct a typing error in the middle of the run.

Single user. One person uses the machine at a time. MS-DOS is the classroom CUI example; a classic desktop Windows is a single-user OS with a GUI (one person at the keyboard, even if several programs are open). The lab PC Anil sits at is single-user in this sense: his classmate cannot log in as a second person on that same cabinet at the same moment the way a mainframe terminal farm can.

Multiprocessing. The system has more than one processor (CPU) working together on jobs. Throughput rises; two ALUs can run at once. A dual-core lab PC is a small multiprocessing machine. Do not mix this with multiprogramming (more than one program kept in memory so the CPU is not idle while one program waits for a disk). Books name both; multiprocessing is more than one CPU.

Time sharing. Many users (or many programs) share one CPU by time slices: a few milliseconds each, round and round, so each user feels the machine is theirs. A password at a terminal, a minicomputer or mainframe with many screens, a college server that several labs query — time sharing. Windows on one desk is not “many users in the time-sharing sense”; it is multitasking for one user.

Windows is Microsoft’s family of GUI operating systems for microcomputers. The lab desktop almost certainly runs a member of this family. It is a single-user OS in the sense of the last lesson, with multitasking: more than one application open (a browser and a word processor) while you sit at one keyboard. You work with a mouse (Unit 1 pointing device) on a screen of windows, icons and menus — a WIMP interface (windows, icons, menus, pointer).

After you log in you see the desktop. Icons are small pictures that stand for a program, a file or a folder. Classic icons the books name: the computer (drives C:, D:), Recycle Bin (deleted files wait here until you empty it), folders you create for an assignment. A window is a framed rectangle for one program. Its title bar names the program; buttons minimise, maximise/restore and close. You can have two windows visible and switch with the taskbar.

The taskbar usually sits at the bottom: Start button, running programs, clock. Start opens the list of programs, settings and shut down. Files hold data (a .docx assignment); folders hold files and other folders. Explorer (File Explorer) shows the tree. Path example: a file on the lab disk under a student folder. Control Panel (or Settings in later Windows) changes date, display, printers and mouse. Notepad and Paint are the tiny applications Rapidex uses to show “open, type, save.” Shut down through Start so that files in RAM are written back to disk (Unit 1: RAM is volatile).

Windows is not the Internet and not HTML. It is the OS that can host a browser and a folder of .html files. DOS is the older CUI operating system.

The Internet is a worldwide network of networks: computers and smaller networks joined by agreed rules (protocols) so that data can move. It is not one company’s wire. A college lab PC joins it through the campus link (the modem, leased line and routers are Unit 4). TCP/IP is the protocol family books name for the Internet. The Internet is the road. E-mail, the WWW and search are vehicles on that road — not other names for the same thing.

E-mail (electronic mail) sends a message from one mailbox to another across the Internet. An address has the shape user@domain — for example a student name at a college domain. To is the main recipient; Cc (carbon copy) sends a visible copy; Bcc (blind carbon copy) sends a copy the other To/Cc names do not see. An attachment is a file that rides with the message (an assignment .docx). Inbox, sent, draft and trash are the usual folders. SMTP is the classroom name for sending; POP or IMAP for fetching mail to a PC. E-mail is not the WWW: you can send mail without opening a web page, and a web page is not a mailbox.

The WWW (World Wide Web) is a service on the Internet that joins pages of text, pictures and links. A web page is one document; a website is a set of related pages; the home page is the front door. A hyperlink is the clickable jump from one page to another. A URL (Uniform Resource Locator) is the address of a page: protocol, then the site name, then a path — as in http:// followed by a college site and /notices. HTTP is the protocol that fetches web pages. HTML (next lessons) is the language those pages are written in. The Internet existed before the WWW; e-mail is older than the Web as a popular service.

A web browser is application software that requests a URL, receives HTML, and draws the page on the screen. The books name Internet Explorer; a lab today also has Edge, Chrome or Firefox. The browser is not the search engine: it is the window. Address bar, back/forward, bookmarks/favourites, refresh and stop are the usual controls. A browser can also open a local .html file from the Windows folder without going online.

A search engine is a website that helps you find other pages. You type words (Anil might type “MGSU Bikaner B.A. English”); the engine returns a list of links. It works by crawling pages, indexing words, and ranking results. Google, Bing and Yahoo are the names students meet; the job is the same: find, not browse a URL you already know. A search engine is used through a browser; it is not itself the browser.

HTML (HyperText Markup Language) is the language of ordinary web pages. Markup means you wrap content in tags that tell the browser how to show it, not a 3GL program that the CPU compiles like C. A simple HTML program is a small page saved as a .html file and opened in a browser. Example for the lab: a notice that Anil Sharma, roll 2145, B.A. English, Bikaner, must score 36.

Types of HTML documents. A static page is the same HTML file every visitor receives (a college notice). A dynamic page is built on the server when asked (a result typed from a database) — this unit writes static pages. Bayross also names HTML 4 document type declarations: Strict (clean structure, little old formatting), Transitional (older tags still allowed), Frameset (the page is a frameset, next lesson). The declaration sits at the top so the browser knows which rules to apply.

Document structure. The skeleton is html around everything; head (information about the page: title, style) then body (what the visitor sees). Title is the text on the browser tab, not a heading inside the page. An element is a start tag, content, and an end tag: <p>Anil Sharma</p>. Some elements are empty: <br> (new line), <hr> (horizontal rule), <img> (image, with a src attribute). An attribute lives inside the start tag (src, href, align, border). A hyperlink is <a href="notice.html">Notice</a>: href holds the address the click should open — the HTML form of the WWW hyperlink.

Type and character formatting. Headings <h1> to <h6> (<h1> largest). Paragraph <p>. Line break <br>. Character: <b> bold, <i> italic, <u> underline, <sup> superscript, <sub> subscript (36₁₀ in Unit 2). Older books also use <font> (colour, size, face) and <center>. <pre> keeps spaces as typed. A smallest page: <html><head><title>Lab notice</title></head><body><h1>B.A. English · Bikaner</h1><p><b>Anil Sharma</b>, roll 2145. Pass 36.</p></body></html>.

Tables. A table is rows of cells. <table> wraps it; <tr> is a row; <th> a header cell; <td> a data cell. Attributes the books use: border, cellpadding, cellspacing, align, width. A two-column lab table: heading “Roll” / “Name”, then 2145 / Anil Sharma. Tables can nest and can hold a whole page layout in older pages; their first job is still a grid of facts.

Frames. A frameset document splits the browser window into named rectangles, each showing its own HTML file. The outer file uses <frameset> with rows or cols (for example cols="25%,75%" for a narrow menu and a wide content pane) and <frame src="menu.html"> for each pane. <noframes> holds text for a browser that cannot show frames. A Frameset document type is the matching declaration from the last lesson. Rapidex and Bayross teach a two-pane lab site this way: left list of units, right the notes.

Forms. A form collects input and sends it to a program (the action URL) by GET or POST. <form action="…" method="post"> … </form>. Controls: <input type="text"> (name), password, radio (one of a set: A/B/C/D on a mock OMR), checkbox (more than one tick), submit, reset. <textarea> for a longer comment. <select> with <option> for a drop-down (Semester I–VI). A classroom form: name, roll 2145, paper “Elementary Computer Applications”, submit. GET appends the data to the URL (you can see it in the address bar). POST sends the data in the body of the request — the usual choice for a password. Without a server the form still draws; sending needs a program on the other side, which this unit does not write.

Style sheets. Style sheets (CSS — cascading style sheets in Bayross) separate look from structure. Three places: inline — a style attribute on one tag; internal — a <style> block in the head for that page; external — a .css file linked from many pages so the whole lab site shares colour and font. A rule names a selector and properties: body { background colour; font family; }, h1 { colour; }. HTML says this is a heading; the style sheet says the heading is blue. Character tags (<b>) still work; style sheets are the cleaner way the books add after formatting tags.