file extension HELP

Unix

Unix operating systems are widely used in both servers and workstations. The Unix environment and the client-server program model were essential elements in the development of the Internet and the reshaping of computing as centered in networks rather than in individual computers.

Both Unix and the C programming language were developed by AT&T and distributed to government and academic institutions, causing both to be ported to a wider variety of machine families than any other operating system. As a result, Unix became synonymous with "open systems".

Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration. Unix systems are characterized by various concepts: the use of plain text for storing data; a hierarchical file system; treating devices and certain types of inter-process communication (IPC) as files; and the use of a large number of software tools, small programs that can be strung together through a command line interpreter using pipes, as opposed to using a single monolithic program that includes all of the same functionality. These concepts are known as the Unix philosophy.

Under Unix, the "operating system" consists of many of these utilities along with the master control program, the kernel. The kernel provides services to start and stop programs, handle the file system and other common "low level" tasks that most programs share, and, perhaps most importantly, schedules access to hardware to avoid conflicts if two programs try to access the same resource or device simultaneously. To mediate such access, the kernel was given special rights on the system, leading to the division between user-space and kernel-space.

The microkernel concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a "normal" computer consisted of a hard disk for storage and a data terminal for input and output (I/O), the Unix file model worked quite well as most I/O was "linear". However, modern systems include networking and other new devices. As graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse, and in the 1980s non-blocking I/O and the set of inter-process communication mechanisms was augmented (sockets, shared memory, message queues, semaphores), and functionalities such as network protocols were moved out of the kernel.

Introduction to Mac OS X

Ever wonder why people get so attached to their Mac? Think Mac OS X. At the core of every Mac, Mac OS X is what makes your digital life more simple, more productive, and just plain fun.

It’s easy.

Mac OS X is a celebration of simplicity and common sense. No complicated menus. No obscure commands. Most tasks can be accomplished with just a click or two. And if you ever need guidance, there’s a built-in help system to light the way. Oh, one more thing: Mac OS X is simply breathtaking — and easy to personalize with desktop pictures and screen savers.

It’s advanced.

Making amazing things simple takes seriously advanced technology. Mac OS X is built on a rock-solid UNIX foundation, delivers true 64-bit performance, and incorporates industry-leading animated graphics. The beauty is, you don’t have to know what one word of that means — just start up your Mac and enjoy it.

It’s amazing.

More than an operating system, Mac OS X is a collection of very cool applications. It comes with everything you need to surf the web, send beautifully designed email, video chat, and organize your personal information.

It’s secure.

In a world where PCs constantly do battle with viruses and malware, Mac OS X is a sea of tranquility. Just go about your business and Mac OS X minds the fortress. Your documents are safe even if you share your Mac with others, and you can keep your kids safe by using a rich set of parental controls.

It’s compatible.

It’s a big world out there, and Mac OS X fits in perfectly. It runs Microsoft Office. It has built-in drivers for cameras, printers, and external drives. It plugs right into a PC network. And in case there’s a PC application you can’t live without, Mac computers can even run Windows. Mac OS X is compatible with everything — most of all, you.