posted by Kroc on Thu 24th Aug 2006 20:26 UTC

"GEOS, Page 6"

DeskTop Features

Along the top of the screen there is a "command menu". Just like Mac OS, there is only one menu bar and it displays the menu according to what app is running. Considering that there is no multi tasking at all in GEOS, it makes little difference. The Commodore 64 has a key with the Commodore logo on it - much like the Windows or Apple key on modern keyboards. The menu strip

The 'disk note pad' is the main window that shows the contents of the current disk. It cannot be moved or resized and doesn't have scrollbars. Instead, the page curl at the bottom left can be clicked either on the curl to go forward one page, or on the page behind to go back a page (also accessible with the 1-9 keys). You can have up to 18 pages depending on how many files are on the disk. The disk note pad

There are no file extensions, and no subfolders! The disk contents are a confusing mix of utility applications, key system files and drivers. Whilst files inside of GEOS can have their own icon, normal C64 files from outside GEOS will always show as the 'C=64' folder-like icon. Double clicking these instantly exits GEOS and loads the C64 program.

The GEOS boot disk however is not meant to be a place to store your own files, or your productivity apps. With only 170 KB per disk, each productivity app usually comes on a separate floppy disk. Once GEOS is booted you can switch disks to run new applications. When you exit the application you must insert the GEOS boot disk so that it can load the 'deskTop' application. If you copy the deskTop application to other disks (or use two disk drives) you can avoid massive amounts of disk swapping.

The single button on the title bar is the close button. It does not close the window entirely, but rather 'eject' the disk from the system, leaving the window blank. Clicking on the disk drive symbol on the right of the deskTop will load that disk's contents. Moving a file to the border

The 'border' (the blank area underneath the disk note pad which holds the current printer and the waste basket) can be used to place up to 8 files off of the disk note pad, so that you can change either pages or disks and move the files to the new location. Clicking an icon selects it in inverted graphics, and then clicking again turns the mouse into a ghost of the file icon, allowing you to move it to the border. Files in the border

The icons in GEOS are all 24x21 pixels in size. This is because the Commodore 64's sprites are always 24x21 in size which equates to 3 characters (8 pixels wide) across and almost 3 characters high. Whilst GEOS's icons are not sprites themselves (they could be of any particular size because they are drawn dot for dot on the bit-mapped screen), 24x21 is used so that the mouse pointer (a sprite) can become a ghosted icon in drag and drop operations.

The reason for falling short of three bytes tall is so that when the 8 supported sprite images of 504 bytes each are counted it adds up to 4032 bytes, leaving 64 bytes in a 4 KB block of RAM to control the positions, visibility, order and colours of the 8 available hardware sprites.

The Commodore 64 also included a programmable Interrupt ReQuest controller (IRQ). Every 1-50th of a second, a routine in RAM was called. The programmer could tap into this in order to run instructions before the screen refresh, half way through (or even a few tiny instructions within the time it took for the electron beam to 'fly-back' to left hand side of the screen, from the right). This gave the programmer the power to redirect the pointer to the sprite data halfway down the screen, in order to produce 16 working hardware sprites. 64 simultaneous hardware sprites have been demonstrated using this method!

Table of contents
  1. "GEOS, Page 1"
  2. "GEOS, Page 2"
  3. "GEOS, Page 3"
  4. "GEOS, Page 4"
  5. "GEOS, Page 5"
  6. "GEOS, Page 6"
  7. "GEOS, Page 7"
  8. "GEOS, Page 8"
  9. "GEOS, Page 9"
  10. "GEOS, Page 10"
  11. "GEOS, Page 11"
  12. "GEOS, Page 12"
  13. "GEOS, Page 13"
  14. "GEOS, Page 14"
e p (14)    45 Comment(s)

Technology White Papers

See More