IBM ThinkPad 755CD

An earlier article about PowerPC-based ThinkPad 850 mentioned that the 850 was a close cousin of x86-based ThinkPads of the era. The OS/2 Museum now takes a look at one of those laptops, and interesting laptop in its own right: the ThinkPad 755CD.

ThinkPad 755CD

The 755CD’s claim to fame is the fact that it was the first-ever laptop equipped with a built-in CD-ROM drive. In October 1994, a CD-ROM reader was common but not quite standard equipment for desktop computers, and portables by definition only came with a floppy drive. The 755CD flipped things around and came only with a built-in CD-ROM drive, although it could be swapped out for a floppy drive which used the same UltraBay connector.

Knowing that it was ahead of the competition, IBM promoted the 755CD in non-computer-oriented magazines (e.g. TIME) with an ad featuring Francis Ford Coppola’s kitchen with a 755CD on the counter.

ThinkPad 755CD Print Ad.

But the CD-ROM was just the beginning. The 755CD was a mean (if not entirely lean) multimedia machine: 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 that in a small package, no larger than other contemporary laptops.

ThinkPad 755CD Technology

There were two generations of the 755CD: The initial Oct ’94 model with a 3.3V Intel 486 DX4 processor running at 100MHz, and a Sep ’95 upgrade with a 75MHz mobile Pentium processor. The 486 model continued to be sold alongside the Pentium, and could be upgraded by installing a new processor card.

755CD Processor Board

The units came with 8MB RAM installed on the system board. Memory capacity could be expanded by installing an IC DRAM card or up to two DIMM modules on an adapter card. Up to 32MB could be added, for a total of 40MB. That was quite a lot for a 1994 portable (or a desktop, for that matter).

The chipset was made by Pico Power, a mobile specialist purchased by Cirrus Logic in 1994. At the time, Intel offered no mobile chipsets (the 430MX rectified the situation later). In conjunction with the ThinkPad’s BIOS, the Pico Power chipset offered advanced power management capabilities; more on that below.

Pico Power

Storage was IDE based (both hard disk and CD-ROM). The double-speed CD-ROMs were manufactured by TEAC, the disks were IBM’s own 2.5″ TravelStars. The hard disk was normally the only moving part in a running 755CD. There were no fans and only relatively skimpy cooling achieved through an aluminum heat spreader. This made for very quiet laptops.

The “thick” UltraBay slot housed the CD-ROM but could optionally hold a floppy drive (the connector was compatible with earlier ThinkPads, too). The CD-ROM and floppy drives were hot swappable; lifting the keyboard to access the UltraBay slot would automatically suspend the system and closing the keyboard would wake the laptop up again. Users who needed both a CD-ROM and a floppy drive at the same time had to use a dock or a port replicator (a dock could hold a CD-ROM or a floppy, and both docks and port replicators sported connectors for attaching external floppy drives).

755CD CD

There was just one display option, a 640×480 TFT color display. The graphics chip was a Western Digital WD90C24A2 with 1MB VRAM, capable of driving an external monitor at 1024×768 resolution with 256 colors.

755CD Graphics

Philips SAA 7110 and ASCII V7320 chips on a separate video board added motion video capture and output capabilities.

755CD Video Board

There was an infrared serial port with sensors on the front and the back, as well as a regular serial port and a modem attachment (optional in some models). Standard PCMCIA slots were typically used for storage or network cards.

Audio was taken care of by a Crystal Semiconductor CS4218 chip plus an IBM Mwave DSP. The Mwave DSP was a very interesting piece of technology on its own, a programmable chip with its own OS and scheduler. The DSP was capable of providing a 14,400 and later 28,800 bps modem functionality, 44.1 kHz 16-bit stereo recording and playback, 32-bit channel MIDI playback, as well as Sound Blaster/AdLib emulation. The 755CD came with small built-in stereo speakers. There was also a connector for a custom game port/MIDI cable.

The added thickness of a CD-ROM as well as the video board made the 755CD slightly bulkier than its sister models. The laptop was about 7.3mm thicker, which created an unusual problem—there was too much space inside the system, since the battery and hard disk were the same size as in the other ThinkPad. IBM solved the problem by adding a light plastic spacer which prevented the keyboard from buckling under pressure.

ThinkPad 755CD Software and Power Management

The 755CD laptops came with a big pile of preinstalled software, most of which is unfortunately not available. This included titles such Asymetrix Digital video Producer, Puma TranXit, SofNet FaxWorks Voice, or Mind Path Presentation F/X Pro (the 755CD certainly was a machine to impress!).

The systems were typically preinstalled with PC DOS 6.3 (later 7.0), Windows 3.11, and OS/2 Warp 3.0. Also included was a large set of utilities and drivers, still available from PC BBS mirrors.

There were system management utilities, such as PS2.EXE for DOS and graphical equivalents for OS/2 and Windows. The Easy-Setup in the ThinkPads was very much simplified and many settings were not available. The management utilities supplemented Easy-Setup and provided configuration for the Mwave DSP, video in/out, or power management presets.


Another package was the PC Card Director, IBM’s set of PC Card (formerly PCMCIA) drivers, including card and socket services. The Mwave driver set was the largest and included audio and modem DSP software, as well as a largish set of MIDI samples.

The power management features of the 755CD were very similar to the other ThinkPads of the era and quite advanced. The Pico Power chipset provided clock throttling and system activity detection. There were separate power profiles for running on AC power versus battery.

After a period of inactivity or on command, the ThinkPad could turn off the hard disk, turn off the display, and enter standby mode with the CPU running at very low speed.

The next step was suspend mode, with the CPU entirely halted. One of the ways of entering suspend mode was closing the lid or lifting the keyboard. The ThinkPad was equipped with a small back-up battery 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.

The lowest power state was hibernation. The memory contents and system state were saved to a special file on the hard disk and the laptop was then completely powered off. When powering up again, a special boot record marker directed the ThinkPad’s BIOS to skip normal boot and restore the system state from the hibernation file instead.

ThinkPad Hibernation

Nowadays these features are standard, but having them in 1994 and having them working reliably was anything but standard.

Not surprisingly IBM’s own OS/2 supported the ThinkPads well. OS/2 Warp 4 came with docking, UltraBay, and PC Card support in the base package, and a separate Device Driver Pack CD contained model-specific ThinkPad utilities for the video chip, the Mwave DSP, etc.

The 755CD was also well supported under PC DOS, but DOS did not support the 755CD terribly well. What this means is that while IBM provided a full set of DOS drivers, loading them all (CD-ROM, PC Card, Mwave, as well as device-specific PC Card drivers) put a severe strain on DOS memory. The multiple configuration feature of DOS 6.x was no doubt very useful to many users, but it was just a crutch.

The Mwave DOS drivers bear a special mention. Older ThinkPads (e.g. the 750C) had built-in audio but no Sound Blaster compatibility. The Mwave DSP in the 755CD emulated a Sound Blaster 1.5 and AdLib, though the emulation took up a significant chunk (almost 50KB) of conventional memory. This could easily prevent games from starting.

ThinkPad 755CD and 850 Similarities

The basic design of the shell with a pop-up keyboard was the same. In both cases, opening  the keyboard provided access to a hard disk, CD-ROM, and a battery pack, with optional DRAM module underneath.


Both the 850 and 755CD could use the same IC DRAM modules, although the 755CD was often shipped with a DRAM adapter.

The keyboard with a built-in TrackPoint was very similar, with the same technology and some identical parts. Interestingly, both of OS/2 Museum’s units have trouble with the left TrackPoint button which only functions intermittently but improves with use. That just underscores the similarity.

The processor and chipset were obviously very different, but the peripherals were much less so, despite the fact that the 850 used a PCI bus while the 755CD was an older ISA + VL-Bus design.

Both the 850 and the 755CD used a WD90C24A2 graphics chip with 1MB DRAM. The 755CD only came with a 640×480 TFT display compared to the 850’s 800×600 panel, but some of the older ThinkPad 820/850 models also used 640×480 displays.

Both systems also utilized very similar motion video hardware—ASCII Corporation V7320 in the 755CD vs. V7310 in the 850. The audio hardware was also similar, Crystal Semiconductor CS4218 in the 755CD vs. CS4231 in the 850. The real difference was that the 755CD also contained an Mwave DSP.

In addition, both systems used Intel’s chips for providing core ISA system devices (interrupt and DMA controllers, timers, etc.). In the 755CD it was an 82091AA (Advanced Integrated Peripheral, or AIP), in the 850 there was an 82378ZB PCI-to-ISA bridge.

The CD-ROM drive was mechanically the same in both systems, a TEAC CD-40. However, the drive used a SCSI interface in the 850 (drive model CD-40S) and EIDE/ATAPI interface in the 755CD (CD-40E).

Last but not least, both systems could use the same power supplies and external floppy drives.

The OS/2 Museum Unit

The 755CD was purchased for a few Euro as defective with no information as to its state, just a few photos showing a dirty but not battered laptop. Unpacking the system proved to be an interesting experience. The outer shell was in a very decent shape (for a nearly 20 year old laptop!), somewhat dusty and dirty but with no major scratches and no hinged covers missing. The keyboard was likewise in good shape, only very slightly worn. There shell was cracked near the rear left corner, a common and largely cosmetic ailment caused by very stiff LCD hinges. The laptop had clearly been used but not abused. Unfortunately the unit didn’t seem to power up at all.

Shell Crack

Opening the keyboard showed what was wrong. The laptop had clearly suffered a significant battery leakage. Disassembling the unit started with the hard drive. The disk turned out to be the original 1.2GB Travelstar in excellent condition and worked without any apparent trouble in a USB enclosure, with the caveat that it needed a two-prong USB cable as it needed to draw slightly over 500mA. Based on the disk contents, the laptop had not been booted up for about 10 years. The main battery was junk, though anything else would have been a huge surprise.

Another attempt to power up the system brought a most pleasant surprise—the LEDs came on, the display brightened up, and the ThinkPad came to life, sputtering and wheezing, but thankfully with no passwords. Amazingly, the CMOS battery still worked and the laptop had the right date, just a few hours off.

Now that the system was somewhat alive, it turned out to be the newer 755CD model with a 75MHz Pentium processor and 8MB RAM on board. In addition, there was a DRAM adapter with a single 16MB module, for a total of 24MB RAM. Not bad.

The CD-ROM, the most interesting part of the 755CD, appeared to be toast. It wasn’t detected at all, therefore a BIOS test wouldn’t even run. However, the eject button still worked and inserting a CD would cause the drive to spin up, although it sounded like it had major trouble reading anything at all.

Given the visual state of the unit, it a thorough inspection and cleaning of the system board was in order. The HMM was very helpful in this endeavor, although it was slightly misleading at times. The 755CE section of the HMM was more accurate; it is possible that the Pentium-based 755CD was somewhat more similar to the ‘enhanced’ 755CE models.

At any rate, apart from the mostly cosmetic damage to the aluminum EMI shield and heat spreader, the system turned out to be in excellent shape with no traces of corrosion on the electronic components. The first attempt at re-assembling failed, with one screw and one piece of plastic left over, and a non-working LCD panel (but no trouble with a CRT). The leftover plastic piece was a consequence of the HMM being inaccurate. The other two issues were operator errors; a forgotten screw and an improperly installed riser card connecting the bottom PCB, which is the home of the graphics chip, with the top PCB, where the LCD panel connectors are mounted.

System Board Sandwich

Once the ThinkPad was properly reassembled, things looked far better than before. The core unit worked very well, the notable exception being the CD-ROM reader. The drive no longer appeared dead—it was detected, drivers loaded, and it sometimes managed to read  CD-ROM discs, but it was not reliable. It was no longer clear whether the problems were caused by the battery leakage or just old age. A floppy drive installed in the same UltraBay slot worked well and the connector appeared undamaged, on both the system board and the CD-ROM drive. A replacement CD-ROM fixed that problem.

The cleaning exercise provided a nice opportunity to photograph the insides of an early ThinkPad, and the OS/2 Museum collection now includes a historically interesting vintage laptop.


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9 Responses to IBM ThinkPad 755CD

  1. Calvin says:

    I got a 701cs (butterfly keys!) running Windows 95. It’s suffering some bitrot right now – bad RAM causes it to barely get to Windows without crashing because of registry corruption because of it. At least I got to remove the battery before it caused bad things.

    I also have another – the battery bloated itself shut and bent the frame, and cracked the screen.

  2. Michal Necasek says:

    Wow, a Butterfly 🙂 One day I want to get myself a 701C. What type of battery was the bloated one?

    My current experience is that Li-Ion batteries are the safest, at least the older ones. Ni-MH may leak and recent Lithium-polymer batteries have a tendency to bloat and potentially destroy whatever device they’re in (laptop, cell phone, etc.).

    The worst thing about the “bloatware” batteries is that they can bloat after relatively short time, I’ve seen that happen after 3-4 years.

  3. Calvin says:

    Some sort of nickel one – it’s leaking (didn’t kill the system, don’t know for sure because of the lack of a disk in the spare) and I can’t get it out. The plastic cover came off the battery too. Tried tweezers.

    My “normal” one with bad RAM has a fine battery that didn’t leak or bloat. Removed it for obvious reasons.

  4. Michal Necasek says:

    I had serious trouble with a standby back-up battery in a ThinkPad 755CDV (not the 755CD). The connector was so corroded that the wire snapped when I tried to unplug it. I had a big fight with the connector using needle-nose pliers, all the while fearing that I’d tear the whole connector off the board (in the end I luckily didn’t).

    In a different ThinkPad, I had a hard time removing the main battery; again the connectors were corroded and a serious amount of force was required, far more than I like to apply to electronics. Actually the contacts themselves weren’t even so badly corroded but the electrolyte crystals get everywhere and make things really stick. Nasty business.

  5. Paul says:

    Pretty nice writeup. And nice find on getting the P75 model. I already had a 755CD, but I suspect bad memory, as it would give different trap errors when installing OS/2 Warp 4, and also blue screen with NT 4 and Windows 95.

    I recently obtained a 755CV for around $30, with a broken keyboard shelf. Ended up disassembling both machines and created a 755CDV in the process, which works quite well. Didn’t have any problems with battery leakage or problems reassembling, although I sympathize with the battery leakage problems. 755CE class batteries are the worst. I have rebuilt one battery that does work and lasts around 3-5 hours (Sanyo HR-AUL cells). The 755CDV and CV can both use Li-Ion batteries and have been tested with a 760 battery (amazingly, I have one that lasts about an hour). The next project is to rebuild some Li-Ion batteries.

  6. Ville H. says:

    The Mwave was in theory a clever piece of hardware, but I remember having many problems with them, probably either due to driver/software defects or the DSP just wasn’t really up to 28.8k speeds and audio at the same time. I never used DOS/Win3.1/OS2 with the Mwave ACP modems, just Win9x and NT.

  7. Michal Necasek says:

    I wonder if the Mwave was a victim of the flawed “let’s just put all the complexity in software” thinking. Engineers have a tendency to think that programmable hardware is always better than fixed-function, and like to forget that just because the complexity moved from hardware to software, it didn’t exactly vanish, and in fact the new system is probably significantly more complex.

  8. MiaM says:

    … or the hardware engineers just assumed that the software engineers were on par, while they might not had been, or maybe they weren’t given enough resources to do a good job.

  9. Michal Necasek says:

    The problem is usually not that software engineers are worse (or better), but that a lot more is asked of them. Because it’s just software, right? So it can do anything, right?

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