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A sidebar to the article “The Lisa Computer System,” published in Byte, issue 2/1983, pp. 36.

Reporting on the technical specifications of a computer toward the end of an article is unusual for BYTE, but it emphasizes that the why of Lisa is more important than the what. For part of the market, at least, the Lisa computer will change the emphasis of microcomputing from “How much RAM does it have?” to “What can it do for me?” For example, it is almost misleading to say that the Lisa comes with one megabyte of RAM, even though the fact itself is true. That doesn’t mean that the Lisa is sixteen times better than machines that have 64K bytes of RAM. Nor does it necessarily mean that the Lisa can work on much larger data files than other computers; its application programs each take 200K to 300K bytes, which significantly reduces the memory available for data. It’s more instructive to say, for example, that the Lisa with one megabyte can hold a 100-row by 50-column spreadsheet (as its advertisements state). With this in mind, let’s take a look at the Lisa.

“Lisa” stands for Local Integrated Software Architecture, but it’s really just an excuse to retain Apple’s pet name for the project. The Lisa has a 68000 microprocessor, which is a true 16-bit microcomputer that has a 16-bit data bus, a 24-bit address bus (giving access to 16 megabytes of memory), and 32-bit-wide registers (all but the 16-bit status register). The 68000 in the Lisa runs at a frequency of 5 MHz. It can have up to 1 megabyte of memory with parity and comes standard with one megabyte (1024K bytes).

The video display is a 12-inch monochrome monitor (black and white, not tinted) with a resolution of 720 by 364 pixels. The interlaced image is refreshed at 60 Hz, which eliminates the possibility of eyestrain from subliminal flickering. The video display is completely generated by internal software, so the Lisa can use multiple character sizes and fonts without restriction. It also means that Apple is not restricted to any one style of video image; the designers can radically change the behavior of the system with a new release of software.

The Apple 871 disk drives design (called “twiggy drives” inside the company) are significantly different from conventional floppy-disk drives. Each one uses a 6504 microprocessor as a “smart” interface between it and the Lisa. The drives use special high-density, double-sided floppy disks that have two oval cutouts in the jacket (see photo below). These are essential because the two disk heads, in addition to being on opposite sides of the flat magnetic media, are not pointed at each other with the magnetic media between them, as is the case in all other double-sided floppy-disk drives. Instead, a pad presses the rotating magnetic media to the disk head on the opposite side of the media as is conventionally done with single-headed floppy disks.

The Lisa floppy-disk drive, along with the special floppy disks it uses.
This image can be zoomedThe Lisa floppy-disk drive, along with the special floppy disks it uses.
Each formatted disk holds 860K bytes of information at a density of 62.5 tracks per inch; together the two drives (standard on the Lisa) hold 1.72 megabytes of data. Each drive also contains a mechanism that releases the disk for removal under program control, which prevents the user from removing a floppy disk prematurely. As with other Apple products, the floppy disks rotate only when the drives are reading or writing data, thus extending the lives of both the drives and the medium.

Apple has done several things to achieve its unusually high data density. The designers used an encoding scheme that keeps a constant data density of 10,000 bits per linear inch: this allows the outer floppy-disk tracks, which have a larger circumference, to store more data than the tracks nearest the center of the disk. In addition, the disk-access system software can move the disk heads in fractions of a track width to search for and find the middle of the track. That’s an important feature when you’re reading disks with small variations in track width.

In addition, the Lisa comes with one Profile (Apple’s 5¼-inch Winchester-type hard disk) to the Lisa through its parallel port. It adds 5 megabytes of magnetic storage to the Lisa system, and speeds up the overall operation of the system. Additional Profiles can be added via interface cards.

The Lisa computer is never really turned off. It stores “system preferences” (things like speaker volume and video contrast) and system-configuration information inside the computer. Even when it is turned “off,” it draws enough power to keep the clock/calendar and CMOS memory containing the above information working. When it’s unplugged (for example, when it’s being moved to another location), internal batteries preserve the clock/calendar status and CMOS memory for up to 20 hours.

Inside the Lisa computer. Note the three connectors for expansion boards.
This image can be zoomedInside the Lisa computer. Note the three connectors for expansion boards.
The Lisa includes two programmable serial ports and one parallel port as well as three expansion-board slots, each of which connects directly to the system bus and has direct memory access (DMA) capabilities. Because none of these slots is filled in any “basic” configuration of the Lisa, they are available for future expansion (unlike the IBM Personal Computer’s five slots, most or all of which are used for much-needed video-display and memory cards). Other features include a built-in speaker and a real-time clock (which can be programmed to execute tasks or turn the computer itself on or off at a given time), a microprocessor-controlled detachable Selectric-style keyboard, and a mouse.

I must thank Apple for including something I’ve wanted to see for a long time: unique serial numbers encoded into memory. The Lisa has two of these: an actual serial number and a 48-bit number meant to be used as a “mail address” identification number for a network of Lisa computers. Two unique identification numbers will help to prevent the unfortunate but very real problems of software piracy and the existence of copy-protected disks that won’t work for even their legal user. Software can be “mated” to the serial number of a given machine so that it can be backed up endlessly but will not run on another Lisa computer. True, a persistent few will outwit even this scheme, but it will practically eliminate a manufacturer’s sales losses from copied software.

The Lisa keyboard.
This image can be zoomedThe Lisa keyboard.
An interesting aspect of the Lisa is that it abandons hardware graphics chips like the NEC 7220 for system software that requires the 68000 microprocessor to generate and maintain the video image. At first, I questioned the wisdom of this decision because it makes the 68000 assume a heavy computational burden that could be transferred from software to hardware. But according to the designers, the use of a dedicated hardware graphics chip would itself limit and slow down the system (for a discussion of this, see the interview on page 90). In particular, the 68000 clock was set at 5 MHz instead of the usual 8 MHz to give the hardware just enough time to access the 32K bytes of screen memory during the machine cycles in which the 68000 is not using the address lines. This gives the Lisa access to the video memory that is transparent to the 68000 (hardware graphics chips severely limit access to the video memory) and results in a static-free image. (Much of the static or “hashing” in graphic video images results from the system accessing the video memory while the circuitry is using it to generate the video image.)

A reproduction (at 80 percent) of printing from the Apple Dot Matrix Printer.
This image can be zoomedA reproduction (at 80 percent) of printing from the Apple Dot Matrix Printer.
Apple will also be offering the Apple Dot Matrix Printer and the Apple Letter Quality Printer. Apple’s engineers tested many existing printers, chose two (from C. Itoh and Qume, respectively) that best met their needs, then had the companies produce modified versions with Apple-specified hardware and software changes. Apple needed such exacting print quality because the Lisa software is very demanding of both printers. For example, both printers will reproduce almost exactly both the text and graphics that can be displayed on the Lisa screen. In addition, Apple has created special print wheels for its Letter Quality Printer so that you can print normal, italic, underlined, and bold characters without changing print wheels (quite a nice move – who’s going to change print wheels several times a page just to get true italics?). The amazing thing about the Apple Dot Matrix Printer is that Apple plans to sell it for around $700 (the Letter Quality Printer will sell for about $2100). Unfortunately for Apple II and III owners, these printers’ tricks are done entirely in software on the Lisa and won’t transfer to other Apple computers.

Page added on 15th November 2003.

Copyright © 2002-2006 Marcin Wichary, unless stated otherwise.