Although the Lisa is considered a microcomputer, it was designed by ex-minicomputer designers, and has minicomputer features. For exampled, it contains two CPU's (a Motorola 68000 and a 6504), and a COP421 microcontroller. The main processor is the 32 bit MC68000. The 6504 is used as a dedicated controller for the floppy drives. The COP421 microcontroller is used for the system clock, power management, keyboard and mouse interface.
The Lisa was designed to be a personal computer. This was a huge departure from both from the shared mainframe with multiple terminals model, as well as character, or text based, personal microcomputers computers. Unlike most mini or mainframe machines of the era, the Lisa provided multi-tasking for one user, rather than time sharing for many users.
The hardware design is clean, and contained features from high end micros. For example, it supports virtual memory (via a memory management unit that provides for both application multitasking as well as preventing one application from crashing another), hard drives, a serial communications controller that can talk to mainframes over SDLC, and so on.
The design of the case makes it easy for the end user to service the Lisa. Almost every card/device is user replaceable.
Various operating systems were developed for the Lisa hardware. Of these, the Lisa Office System has had the most influence and impact, and so deserves much of the credit for the significance of the Lisa.
The Lisa Office System is a very sophisticated OS that at its core has a lot of similarities to Unix (multitasking, virtual memory, MMU, named pipes as files, device control as files.)
On top of this the user is presented with a highly polished graphical user interface that uses a document oriented metaphor instead of the application oriented model of other computers. For example, you don't run LisaWrite to compose a memo. Instead, you tear off a sheet of stationary to compose your memo. You could then open a LisaCalc spreadsheet and copy and paste data into the memo from the spreadsheet. This is done through a mechanism similar to OpenDOC, or OLE (renamed to ActiveX.)
Users don't have to use the "save" command in a File menu on documents unless they want to ensure that recent changes have been written to the disk, or want to immediately save and put away the file (which closes it).
There also is no File Open or File Save dialog box, which to this day plagues every modern GUI out there with a miniature finder/explorer that doesn't quite have the same functionality as the real thing, and causes frustration. This completed the illusion that icons expanded themselves to documents, or better said, that icons are documents. The Lisa had it right
Multiple documents can have the same file name. If you duplicate a LisaWrite document, you get two copies, both with the same name, without having a conflict! This is because the desktop names on the Lisa are virtual. Underneath the pretty GUI, the file system names things uniquely. Think of it this way, when a user makes a copy of a document for another using a photocopier, there are now two identical copies. The user doesn't have to explicitly rename one of them, or worry about document names.
The user never sees any of the underlying operating system files, so they can't harm the operating system by deleting its files.
The Lisa Desktop is able to split a file that is greater than a 400K floppy across multiple floppies. When you attempt to copy it back to the hard drive, it asks you to insert the next floppy and says/The Lisa is reconstructing "filename" on "hard disk"./ You can back up your hard drive by simply dragging it to an empty floppy, and the Desktop Manager will ask you for another disk, and then another, until you have made a full backup.
Users don't need to launch a separate program to do backups.
The Lisa also has features such as a built in screen saver that after a few minutes of inactivity will dim the screen to a user specified brightness.
Unlike most personal computers that have a big red switch to control power, the Lisa uses a software managed power supply. When the user presses the power switch, it acts as a special keystroke; instead of just powering off, the Lisa Office System puts all the files "away" (saving the changes), and then, once it is safe to do so, it tells the COP421 controller to power the Lisa off.
On the next power up, the Lisa will open all the windows and opened documents to the exact position where the user left off
This is similar to hibernating, sleeping, or standby on modern computers. Yet, all of this is done without swapping all of the Lisa's memory to disk, or keeping the main CPU in a low power state to preserve the contents of memory!
Instead, every Tool (Lisa Application) remembered where the user left off and resumes to the same position the next time the Lisa is powered. Compared to "modern" software packages, where it's up to the programmer to provide some option to save state, but requires the user to explicitly do so the next time that application is launched.
Many of the features of the Lisa hardware and Lisa Office System were lost as Apple switched to the Macintosh instead. Some, over time made their way back in, others showed up in various other operating systems, but none have the same look and feel as the Lisa, nor the same tight integration between applications, documents, operating system, and hardware. The only other machine with this high level of integration would be Apple's Newton.
(No, before you ask, in Lisa Office System, one does not drag the floppy to the trash can to eject it)
Lisa is a much nicer equivalent of a modern day office suite (with memory/storage/CPU limitations) but existed over 20 years ago.
These are the features that make this a great, and very unique machine, which was truly ahead of it's time.
Sadly, Lisa was replaced by a machine that was its mere shadow. The original Mac 128 was considered crippled when compared to the Lisa. With only 128K of RAM, it could only run one program at a time. To do any real work, an external floppy drive was required. The alternative was a horrible incessant swapping of floppies every few seconds.
Fortunately, the Mac has evolved over time, and while it lacks the same level of integration as the Lisa did 25 years ago, it has matured quite nicely.[LisaFAQ] (Comment on this answer)