In the Beginning the Mac was new and very different from the PC (and neither of them ruled the industry if there was a king, it was the Commodore 64, although the Commodore was old and infirm). The PC ran MS-DOS, normally had a text-based screen (usually black with amber or green characters on it), did not have a mouse, had a large and somewhat esoteric keyboard with keys like "F2" and "Page Up" and "Print Screen" and "Num Lock", had one or two 5.25" floppy disk drives, and each commercial application, called by PC users a "program", had its own repertoire of keystroke commands (some with GUI menus, others without, but each one unique unto itself). The Mac ran the Macintosh operating system, had a pixel-based black-and-white screen, depended from the start on a mouse, a GUI with double-clickable icons to represent commercial applications, folders, or documents, had a small keyboard which, aside from the ⌘ key and the Option key, had essentially nothing on it that hadn't been on a traditional typewriter's key layout; It sported one 3.5" diskette drive, with an optional second external one; and all of its applications shared a set of standard keystroke commands which were replicated in the equally standard overhead menus from left to right, FILE MENU had or very soon would have ⌘-N for New Document, ⌘-O for Open, ⌘-W for Close Window, ⌘-P for Print, ⌘-S for Save, and -⌘Q for Quit; EDIT MENU, right from the very start, had ⌘-X for Cut, ⌘-C for Copy, and ⌘-V for Paste, and pretty quickly picked up ⌘-Z for Undo. And they were always there, those two menus, in that order (no one put the Edit menu on the far left, etc). And they had no simple way to speak to each other. There was no file sharing software/networking protocol, as this was in the days before networking. With different floppydrive hardware, no way to move data back and forth via floppy disk. You could rig a serial cable between a Mac and a PC and use XModem or YModem terminal protocols to exchange files, but file formats were incompatible there were no applications in common, and the PC used dot-threeletter file extensions to explain files to the OS and its apps, while the Mac used a paired set of metadata fields, "file type" and "creator code", stored in the resource fork (of which the PC's file format had none), to categorize the file. You could exchange plain text files and that was about it! And even then, the line endings, representing the point where the text shouid wrap to a new line, were different, so once you had the text file, you'd have to replace peculiar box-shaped characters with hard returns. Oh, and upper ASCII (anything above the first 128 characters) was encoded differently, so © might come out as Í and so on, in either direction. By the time I bought my first Mac, the PC-using world had largely embraced the 3.5" diskette (althought most of them had a 5.25" drive as well) and the later editions of the Mac SE, such as mine, had drives that could read hi-density diskettes and also PC-formatted diskettes, although since they were software-formatted differently, you had to use this awful thing called Apple File Exchange, a program with one halfscreen window showing the Mac universe and the other halfscreen showing the contents of the foreign PC-formatted floppy, with buttons to move and translate PC files to Mac (changing line endings, adding file type codes) or vice versa (changing line endings, adding file extensions). Oh, and there was networking. Macs had AppleTalk (LocalTalk, over the serial port), long present to allow several Macs access to a single LaserWriter printer, but by now letting you mount a server volume and access its files as if they were local! The PC meanwhile had this thing called Novell and they could do it too, although of course the two protocols had no overlap on either hardware or software protocol. Somewhat later, the PC world got "NetBEUI", which was built into the OS and not an add-on from Novell, so they had two. A couple of 3rd-party companies brought the two systems closer together: there was this expensive thing called MacCharlie, which was an entire PC that would clap onto a Mac and use its monitor. I never saw anyone with one of those. But then Dayna made the DaynaFile, a 5.25" drive for the Mac as an external SCSI device, and an INIT (system extension) called DOS Mounter, and quickly found a market for DOS Mounter above and beyond DaynaFile owners: because it would mount a DOS-formatted diskette right on your desktop just like a Mac diskette, right there in the Finder! Also, I think Farallon put out a hardware-software kit that would let PCs run AppleTalk (LocalTalk). And Macs could get ethernet (thin coaxial, in those days, not 10-base-T) and install a Novell networking stack and be part of a Novell network. Microsoft was one of the first companies to have applications of the same name on the two platforms that would save files in the same format, so that reading them in on the other platform didn't require "translating" all you needed to do was stick a PC-style file extension to go from Mac to PC, or have Dayna DOS Mounter (and later, Apple's own native File Exchange Control Panel) assign a file type and creator code based on the PC file extension, and you were good to go! PCs had expansion ports ISA card slots. Beginning with the Mac II, Mac had expansion slots too: NuBus. Incompatible, of course.