The Mac, although popular with its supporters, accounts for less than one tenth
of the computer market. This means that you’re bound to encounter data
from other machines — or even have to use one!
Computer Types
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The User Interface
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  Every type of computer has an operating system (OS) that suits its own
microprocessor. Prior to the MacOS most systems didn’t use a standardised
method of passing instructions to the computer or user interface.
User interfaces come in several forms:-
Command Line Interface (CLI)
Probably the most off-putting interface of all time, as used in early mainframe computers and in home computers based on the CP/M-80 and MS-DOS systems. It presents a prompt character such as A> or $, plus a cursor that flashes in an menacing manner.
This is fine if you know what to type — if not, you waste hours leafing through an incomprehensible list of codes. And when you enter something you’ll probably get an unhelpful error message. If you like crossword puzzles you’ll love this interface! Advocates of CLI like the immediacy of keyboard control — undoubtedly you’re less likely to make mistakes. But, there again, you’re less likely to do anything at all!
Menu-initial Interface
A slight improvement over the CLI — you see a series of letters without any clue as to what they mean. Each of these menus can lead you on to another equally baffling list.
Menu-word Interface
Similar to the above but with meaningful words in the menus. Since the selected word is highlighted this interface also known as a Moving Bar Interface. This highlighting effect was carried over onto the pull-down menus used in the Mac.
Menu-driven Interface
Widely used in modern mainframe systems. You’re presented with a menu page that fills the entire screen — having made your selection you’re often led into further pages. As with all of these rudimentary interfaces it’s often difficult to get back to the starting point after making a wrong turn! Even so, this interface remains popular for strictly-controlled environments as required in service industries or emergency services.
Graphical User Interface (GUI)
This interface, derived from original work at the Xerox Palo Alto Research Center (PARC), uses pull-down menus that occupy much of the screen whilst a selection is being made. It first appeared in the Apple Lisa and was further developed as part of the Mac’s operating system. The interfaces in Windows and in the Presentation Manager component of OS/2, both used on PCs, are also based on the original PARC concept.
All of these systems use a Window Icon Mouse Pointer (WIMP) environment. The term cursor is often used instead of pointer — strictly speaking a cursor is only used in a CLI.
Operating Systems
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  The code used to construct an operating system must match the hardware in a
computer, including its microprocessor. Although a computer can emulate the
behaviour of another processor, allowing it to run applications intended for the
other machine, the results are rarely fast enough to be acceptable.
Having said that, Apple have successfully used 680x0 emulation on their PowerPC-based machines, allowing the MacOS to be moved across from its original microprocessor.
Apart from professional workstations such as Sun, DEC Micro VAX and Next the computer industry is dominated by the PC and its associated operating systems. The following list gives a short summary of some of the systems you may encounter:-
VMS
Virtual Memory System (VMS) from Digital Equipment Corporation (DEC) is used for multi-tasking and multi-user systems on mainframe VAX and MicroVAX mini-computers.
MacOS
  The Mac, introduced in 1984, was based on the 68000 processor. Unlike other
systems it uses routines, kept as resources in system ROM, to give a consistent user
interface in all applications whilst using minimal memory or disk space.
Unfortunately the Mac’s unique character is its worst enemy. For example, it uses its own QuickDraw graphics instead of PostScript. When you use a PostScript-based application its software has work alongside QuickDraw — anyone with a 680x0 Mac and a PostScript application knows how slow this can be!
PostScript first appeared in fonts for the LaserWriter. Unfortunately Apple then confused everyone with their own TrueType fonts — these fonts even found their way onto PCs! Perhaps the promised OpenType will clear up the mess.
It was so easy in the beginning — just MacWrite, MacPaint and a few TEXT and PICT files, and hardly any extensions. Now we have to cope with PostScript files, EPSFs, TIFFs, GIFs and much more — all the junk from other nasty computers! A glance inside a modern System Folder is frightening, almost as bad as Windows. Wouldn’t it be nice if Apple could simplify it all down again and build all those extras into the System?
The new PowerPC Platform (PPCP) Macs will run Windows NT and other alternative operating systems. Although a threat to the Mac OS this might not be so important in the long run — if Apple keeps producing software like QuickTime they needn’t worry!
MS-DOS
  International Business Machines (IBM) launched its Personal Computer (PC) in
1981, based on the 8088 processor — followed by the 8086, 80386, 80486 and later
versions, including the Pentium processor with its Intel Inside trademark.
The PC uses the Microsoft Disk Operating System (MS-DOS), also known as the Personal Computer Disk Operating System (PC-DOS) or simply DOS. Its undoubted success is due to the way in which IBM allowed other manufacturers to produce compatible machines.
The original form of DOS is incredibly efficient in terms of memory and disk space. The introduction of a GUI by means of a Windows front end isn’t so good! Several GUI system variations are used, including Windows NT and Operating System 2 (OS/2).
UNIX
UNIX is a established CLI-based operating system, originally devised by Bell Laboratories for mini-computers. Apple/Unix (A/UX) software lets you run UNIX applications on any Mac and supports true multi-tasking (two application in the foreground at once). It can be used with AppleTalk or TCP/IP over an Ethernet network.
A GUI can be added to any UNIX or A/UX system by means of X Window software. It also lets you run applications designed for DEC and Sun workstations — including computer-aided design (CAD) software. Some Mac applications can run directly from within A/UX. The Apple Macintosh Applications Environment software enables any suitable RISC-based workstation to run Mac applications.
Others
Various CLI-based operating systems have come and gone. These include Apple II ProDOS, based on the 6502 processor, and TRS/DOS and CP/M-80, both built around the Z80 device. Control Program for Microprocessors (CP/M) was a forerunner of DOS.
Using an DOS PC
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This section provides a quick summary of DOS terminology and usage.
 
Entering Commands
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Since DOS uses a CLI it’s vital that you have a printed list of commands available and that
you fully understand the syntax that’s used in them. When the machine’s ready for a new command it displays a command prompt, usually with a flashing cursor. During certain operations it provides other prompts that are the DOS equivalent of dialog boxes.
All commands begin with a command name, often followed by parameters and switches to indicate how the command should operate. Parameters usually specify the item, usually a file or directory, on which the command or batch program will operate.
A switch can be entered after a some command names to set certain options — for example the PRINT command can include switches for printing options. The simplest switch is a slash followed by a letter — others are more complex.
Commands such as DIR and TYPE provide you with information on your screen. COPY and RENAME also keep you informed of progress. Output redirection lets you retain this screen information as a .TXT (text) file for examination at a later date. Similarly, input redirection lets you prepare your commands as a .TXT file that can be implemented later
A pipe can feed the output of one command into the input of another command.
Wildcarding lets you select a group of files according to the contents of part of their names. You can then work on this group as with a single file. This is one of the few areas where DOS is superior to the Mac OS.
MS-DOS Data Storage
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Most types of computer store disk files in a similar way. Each volume (hard disk, partition or diskette) has a single root directory, created during formatting, where all files are stored — on a Mac this is the window that first appears when you open a volume. To this directory the user adds trunk folders and branch subfolders — on a Mac each directory or subdirectory appears as a folder. Finally the user adds leaves, the actual files.
The command DIR produces a directory list showing all the files in the current directory. A path is a list of directories that you must pass through to reach a destination file or directory. DOS uses a backslash to separate adjacent directory names. Absolute paths begin with a backslash and start at the outermost directory. Relative paths begin with a directory name and start from the current directory. The name ‘..’ is a shortcut for the current directory’s name.
When the DEL command is used the file’s entry in the directory is removed — this is the same as trashing a Mac file and emptying the Trash.
In a DOS drive the internal floppy drive is assigned the letter A, any external drive is B and the main internal drive is usually C.
Batch programs
Batch programs are similar to a macro. Firstly a .BAT batch file containing a series of commands must be prepared and the machine told to execute it. You can use the LOG command to create a log file that can be run as a batch program. After the LOG command you can enter the ‘macro’ commands — you simply stop logging when you've finished.
The AUTOEXEC.BAT file is a special batch file, launched at startup, which sets the preferences for your computer. Global variables store temporary information during the execution of batch programs and the preferences extracted from AUTOEXEC.BAT.
Other Hardware Features
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PCs usually come with standard serial ports (called communication ports, with different connectors to a Mac) and use a Centronics interface to connect a PC-style printer. A Joystick, trackball or mouse can be connected to a serial port or via a PS/2 connector.
Most PCs don’t incorporate integral sound inputs or outputs — you may have to install a separate sound card such as Sound Blaster.
