CompuThink PET Memory Upgrade and Hard Drive
Posted: Sun Jun 26, 2005 9:10 pm
I wanted to correct and enhance the info on the Compu/Think ExpandaPET and Disk Drives.
The ExpandaPET expanded memory to full 32K for BASIC and another 8K as disk drive buffering above the memory mapped screen memory of a PET 2001.
Compu/Think beat Commodore to market by almost a year with disk drives for the PET in 1978.
Richard Tobey designed the ExpandaPET and disk drive interface hardware.
Mike Korns wrote the DOS for the drive system. This was shimmed into the parser loop of the ROM basic parser via a zero page hook, so that enchanced disk control commands could be used from Basic. After you started a PET you had to make a SYS call in basic to activate the DOS.
The Compu/Think disks were the fastest for their time and for many years after Commodore introduced their drives, because the 8K memory above the screen memory was used as a disk track buffer that allowed a complete diskette track to be loaded in a single revolution of the disk. Thus a Compu/Think disk could load and write very, very quickly compared to other products.
Compu/Think went on to create their own product that was also 6502 based called The MiniMax. This was a 2mhz 6502 with a 12" 80x25 screen, full keyboard and numeric pad, plus 2 8" or 5.25 floppy drives.. It was introduced in 1979. LAter they changed their name to Momentum Computer and introduced one of the early 68000 + Unisoft Unix servers that would serve up to 16 terminals.
I worked with and later for Compu/Think in the late 70s and early 80s.
The ExpandaPET expanded memory to full 32K for BASIC and another 8K as disk drive buffering above the memory mapped screen memory of a PET 2001.
Compu/Think beat Commodore to market by almost a year with disk drives for the PET in 1978.
Richard Tobey designed the ExpandaPET and disk drive interface hardware.
Mike Korns wrote the DOS for the drive system. This was shimmed into the parser loop of the ROM basic parser via a zero page hook, so that enchanced disk control commands could be used from Basic. After you started a PET you had to make a SYS call in basic to activate the DOS.
The Compu/Think disks were the fastest for their time and for many years after Commodore introduced their drives, because the 8K memory above the screen memory was used as a disk track buffer that allowed a complete diskette track to be loaded in a single revolution of the disk. Thus a Compu/Think disk could load and write very, very quickly compared to other products.
Compu/Think went on to create their own product that was also 6502 based called The MiniMax. This was a 2mhz 6502 with a 12" 80x25 screen, full keyboard and numeric pad, plus 2 8" or 5.25 floppy drives.. It was introduced in 1979. LAter they changed their name to Momentum Computer and introduced one of the early 68000 + Unisoft Unix servers that would serve up to 16 terminals.
I worked with and later for Compu/Think in the late 70s and early 80s.