Wikipedia rejected this article I made for the IBM Thinkpad 755, and the 755CD in particular. I reviewed it twice and the second time cited 11 sources, with 5 of them being IBM's own originally-published press releases from 1996 and 1997, hosted on the original IBM.com website. Wikipedia moderators rejected these citations from IBM because IBM was not a trusted source on the IBM Thinkpads. What a bunch of dickheads.
Anyway. Having dismantled and rebuilt a massive pile of these, I felt it need to document some of the things I'd discovered for other collectors or interested parties.
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.
755CDV
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.
NASA
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.
And some other notes about some of the 755 series...
The 755cx is a FDD-only thinkpad. And the FDD is non-removable.
355,360,370,750,755C,755CS - all share the same ribbon / interposer connector layout, albeit with different combinations of connectors used for mono, colour, and touch screens;
but different from:
755CD, 755CE, 755CX (and the V variants of all these) use a different physical layout of ribbon / interposer connectors so are not compatible.
The 310, 340/345, 365 use different cable/connector arrangements again as they're not really 360/750/755 models internally.
Q: Why are the 755CD, 755CE, 755CX ribbons different from all the others?
A: They use the same base WD90C24 chipset, driving DSTN or TFT panels at the same resolutions*, but a different interposer card off the systemboard to present all the connections in a slightly different arrangement. At a trivial level this is what stops later 755 -> earlier 755 screen/lid swaps from being simple plug'n'play, e.g. 755CX SVGA TFT lid to 755Cs base unit. We've also speculated as to whether the interposer cards were interchangeable but without stripping down two working machines on the bench it's just speculation!
Q: Did all CX machines come with only floppy?
A: Yes, only the CD(V) had the deep chassis capable of taking the CD-ROM, CE, CSE, CV, CX were all the same depth as the previous 755/750 so floppy only.
Q: Which machines had memory soldered onboard and which ones had the internal/base memory on a seperate daughterboard (only, from memory, accessible by disassembling the entire machine)
A:All soldered onboard:
355* - 2MB
360*, 370C, 750*, 755C, 755Cs - 4MB
All on a daughter card:
755CD(V), 755CE, 755CSE, 755CV, 755CX - 8MB
The base memory daughter board on these later models is as accessible as the heater matrix in a car - first thing assembled into the chassis then all the rest put on top & around! You can see why the 760 introduced the little door on the bottom
Really the 755CD(V), 755CE, 755CSE, 755CV, 755CX should be considered the ThinkPad 755+ or 757 or some such - they were distinct enough (in parts and architecture terms) from the previous 755 to share few electronic parts (system board, audio, screen, RAM arrangement, ...) and thereby sit as a distinct model between the 755C/Cs and the 760C/CD.