Mac OS and the 128K Macintosh

Apple began selling the Macintosh in 1984. It’s revolutionary graphical user interface (GUI) would forever alter the course of the home computer industry. Although the concept of the GUI was not new, Apple was the first to bring an effective one to market in a package that many could afford, the Macintosh 128K.

This Macintosh graphical operating system offered many advantages that were revolutionary in 1984. WYSIWYG (what you see is what you get) fonts that could be viewed on the monitor just as they would print on paper changed the very nature of desktop publishing and word processing. Graphical design became much easier and a whole new industry based on computer graphics sprang up around the Macintosh. Macintosh ease of use sent IBM and Microsoft scrambling for a comparable system.

All this revolutionary power did come at a price. The Macintosh 128K performed more system maintenance functions than traditional microcomputers of the day. When you started a Macintosh, the system had to load not only the Finder but also other essential information, such as the system fonts and icon shapes. The Finder often recreated the Desktop file for all disks currently known to the system. Older microcomputers did not have equivalent functions.They used a single built-in dot-matrix character font for everything and few or no graphics, depending on what program was running. Icons, windows, and special fonts were considerably more difficult to describe programmatically than the primitive text-line interface of other contemporary computers, and thus the Mac’s visual interface took longer to load and draw on the screen. Furthermore, the graphical environment took up a large amount of the Mac’s anemic 128K total available system RAM.

The GUI taxed the Mac’s system resources to the maximum. In order to increase the efficiency of the Mac and free up precious RAM, the Macintosh development team chose to hard-code many of the Mac’s low-level functions and system-wide resources into the ROM chip. This negated the need to load everything into RAM from the system disk. Macs from 1984 to the late 1990s, were to a great extent, ROM machines. This arrangement saved on the amount of RAM consumed by the operating system, but made the system software much more difficult to upgrade. Future Mac OS upgrades patched the ROM code since it could not be changed.

In 1984, disk storage was extremely expensive. A 10 MB hard drive could costs several thousand dollars. A hard drive was not originally available for the Macintosh, nor did the device have a fast bus like SCSI available to connect an external hard drive. However, the Macintosh had a connection port for an external floppy disk drive. The Macintosh used the relatively new and expensive 400K, 3.5-inch floppy disk drive manufactured by Sony. The 400K disk drive was fast and had about twice the storage capacity as the industry standard 5.25-inch floppy drive. Mac OS was optimized to run on 400K floppy disks, but there was not much space to spare. In order to boot a floppy to the Macintosh environment, it was necessary to include the operating system along with any program files on each floppy, or in the case of an external disk drive, have at least one disk drive running Mac OS.

The early Macs were typically slower than other contemporary microcomputers. This was the price that the Macintosh paid to be the first graphical operating system specifically designed for home use. It is quite remarkable that Apple was able to pull off such an effective graphical operating system using rather sparse hardware. A hard drive would have sped things up considerably but at the time, hard drives were exceedingly expensive, typically costing more than $2,000 for 10 MB or less. Due to the Mac’s sparse 128K RAM, the system often had trouble copying files between disks, which made disk swapping a common occurrence on the original Mac. The Mac could only move what it could store in its RAM at any given time. The user would have to cycle through the data as the Mac would copy all it could into RAM, ask the user to insert the target disk, copy the contents held in RAM to the target disk, and then ask the user to again insert the original disk, and so on, until the file was moved.

Most of the Macintosh operating system resided in ROM. The rest was stored in a file named System on the startup disk. There was no command line interface. The System file was read from the disk into RAM when the Macintosh booted the disk. The System file added to or modified the ROM. The System file contained information such as the specific keyboard layout, font data, utility programs, desk accessories, and warning and advisory messages. This setup gave Apple a huge advantage in the foreign markets. Storing information on disk that made changes to font or keyboard layout simply meant changing the System file. Apple was able to effectively sell to foreign markets by tailoring the System file.

Another important program that was stored on disk and read into RAM at startup was the Finder. The Finder included many functions traditionally performed by the computer’s operating system. It handled most operations that involve disks: creating the disk window with its file icons, copying files, copying disks, and so on. The Finder didn’t work alone. It used many programs in the ROM for actual disk access, in effect acting as a liaison between the user and the ROM programs that controlled the disk drive. For each disk, the Finder created a hidden Desktop file to hold information about each file on the disk. The Desktop files remembered such on-screen details as icons associated with the file and the size and format of the disk’s window on the screen. It also noted whether a file was an application program or a document.

Mac OS in the original Macintosh was the quantum leap that propelled Apple to forever change the way the world interfaces with computers. Their solution was by no means perfect and represented a compromise due to the cost and capabilities of the hardware at the time. But for what Apple had to work with, they did a masterful job of getting the most out of their equipment. It is a testament to the work of the original Macintosh team that many of the constructs mentioned above remained in use for the market life of Classic Mac OS.


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