Draft:IBM ThinkPad 755

Introduced in June 1994, the IBM ThinkPad 755 series was a direct successor to the shorter-lived 750 series and aimed at the professional / enterprise market. The 755CD was the first notebook computers to incorporate a built-in CD-ROM optical drive, mounted in the Ultrabay.

The 755 series shares many aspects of design and hardware with the 355/360/370 series which was priced and marketed to the consumer market.

All 755 machines came with 4Mb or 8Mb RAM installed on the system board, with earlier models being soldered onto the motherboard and later models using a detachable daughter-board, accessed by completely disassembling the machine. Addtional memory capacity could be expanded by installing an IC DRAM card or up to two DIMM modules on an adapter card underneath the CD-ROM or floppy drive. Up to 32MB could be added, for a total of 40MB.

Later machines which had originally shipped with a 486 DX4 processor could be upgraded to Pentium 75Mhz by replacing the CPU which sat on it's own daughterboard.

All machines were offered with a NiMH main battery, with a Li-Ion battery as an optional extra.

755CD
The 755CD was an early multimedia machine incorporating hardware video playback acceleration, composite and S-Video input and output, built-in stereo speakers and a microphone, a MIDI interface, a DSP chip with audio, modem, telephone, fax, and answering machine functionality. - all within roughly the same-sized chassis as earlier machines.

The CD-ROM drive could be swapped with a 3.5" floppy drive by unclipping the keyboard and lifting it up on hinges, sending the machine into hibernation mode, swapping the hardware and closing the keyboard lid, waking the machine up again. If you needed a CD-ROM and floppy disk drive to be connected in tandem, you could still connect an IBM floppy drive to the propietary IBM connector on the side of the machine.

The CD-ROM unit, as well as the additional video processing hardware made the 755CD about 7mm thicker than the other 755 models, meaning IBM incorporated a lightweight plastic spacer on a hinge which filled the excess space above the battery and hard drive, under the hinged keyboard.

IBM felt so strongly about the selling power of the 755CD even outside of the enterprise market, they marketed the machine in non-computer-oriented magazines with an ad featuring Francis Ford Coppola's kitchen with a 755CD on the counter.

755CV/CDV
This unusual variant incorporated a lid with a removable back panel so that the Thinkpad could lay flat, ontop of an Overhead Projector (OHP) and display the VGA graphics to a much larger audience.

Use on the NASA Space Shuttle
When NASA put out a competitive bid for the next Payload and General Support Computer (PGSC), IBM bid the ThinkPad 755C, which was selected as the new PGSC in 1994. The first PGSC ThinkPad flight (as opposed to an experimental flight) was in 1995. An IBM ThinkPad of differing models were on every Shuttle flight since.

Preservation
The premium finish of the 755-series used an iteration of a then-popular rubber-coating for the lid which does not age well, due to it being easily scratched and degrading over time. Degradation is thought to be caused by excessive warmth, moisture and accellerated by anything touching the surface for an extended period of time. Some owners embark on making the lid more user-friendly by removing the top coating to reveal a satin or bare-metal surface underneath or a straight swap with some iterations of the 3xx-series which are chassis and screen compatible but without the rubber coating applied at manufacture.

All 755 models were equipped with a small, 3-cell, back-up battery, situated underneath the optical/floppy drive which could keep the system suspended without completely losing power even when the main battery was removed. This feature allowed the main battery to be swapped without powering off the system. However these batteries are now highly suseptable to deterioration, causing corrosion around the battery and up the pair of cables into the motherboard.

Later Lithium batteries and faster optical drives from the 760-series are cross-compatible with 755 machines, however 755-series peripherals are not compatible with 760-series machines.