GEOS made good use of the many expansions available for the Commodore 64. As well as supporting two disk drives and many printers, you could also purchase a RAM expansion to add 128, 256 or 512 KB of extra RAM to the system. The biggest upgrade, late in the life of the C64, was the SuperCPU - a 20 MHz upgrade module!
3.5 How To Get GEOS
The OSNews Contest Rules state that the OS must be "available to the public for download or purchase". GEOS is available as a free download, and can actually be purchased, as a set of 5¼" disks with manuals! I personally own a GEOS 1.5 disk set with manual.
Get an Emulator
In order to run GEOS on your PC or Mac, you will need a Commodore 64 emulator to simulate the hardware. I recommend these emulators for the necessary emulation accuracy needed to run GEOS on PC/Mac.
CCS64 - Windows
Has 99.9% emulation accuracy and still in active development (for over 10 years). CCS64 can emulate almost every last timing quirk of the real hardware and thus is accurate enough to run GEOS (which does contain some extremely clever hacks that can fool most emulators)
Make sure to enable the mouse by pressing F9 to bring up the menu and navigate to the input section. Also, for accurate disk speed (i.e. slow), go to the Special menu and disable 1541 Turbo speed or GEOS may fail to boot.
Power64 - Mac OS 9 / X
There are not nearly enough emulators on Mac OS X :(. Power64 is a shareware app that emulates the C64 accurately enough to use GEOS. Whilst Frodo is free it is not accurate enough to run GEOS; it hangs at the boot screen. Power64 has excellent mouse support and is ideal for running GEOS. Although it's not a 'universal binary', it runs without flaw under Rosetta on Intel Macs.
The VICE Emulator is also capable of running GEOS on just about every other alternative OS available. Configuration is much more complex, and if you are technically inclined you can compile the source code to produce an X11 app for Mac OS X for free.
Download the GEOS disk images
GEOS was made available for free download in February 2004 by CMD, makers of modern day Commodore add-ons (like the 20 MHz SuperCPU) - see the Slashdot article.
Instructions on downloading GEOS and getting the disk images available here:
Follow the 'I Agree' link, and then the first link labelled 'go here'. Download the GEOS 64 '1541 boot disks'.
3.6 Booting GEOS
GEOS requires no installation as the Commodore 64 has no mass storage besides a floppy disk drive, and GEOS comes on floppy disks anyway.
Attach the 'GEOS64.d64' disk image to the emulator on drive 8 (the first disk drive on a C64) and then start the emulator. Most emulators will allow you to double click, or 'open-with' the .d64 file with the emulator to attach the disk automatically.
This is the Commodore 64's normal OS. A text-mode command-driven system. In normal configuration, the system reserves just 38 KB for writing BASIC programs. The C64's architecture is incredibly flexible however, and by switching out the ROM shadows in the upper areas of RAM, you could free up almost the entire 64 KB (if you wrote your own IO drivers). GEOS itself ditches a large amount of the default system to fit into the memory available.
load"geos",8,1and press return. Don't hold shift otherwise you'll get symbols instead of letters. The C64 had a series of ASCII-like symbols printed underneath each key. When in normal mode, holding Shift and pressing a key would display the symbol, allowing you to draw ASCII art in the C64 character set. On the C64, this character set is known as PETSCII, as in PET-ASCII (The Commodore PET was an earlier education market computer).