ThinkPad 755

ThinkPad 755C and 755Cs

IBM announced the ThinkPad 755 series in April 1994 and released it the following month on May 17.^[3][4] It replaced the previous ThinkPad 750 line as IBM's high-end offering in their ThinkPad family of notebook computers.^[3] The first two models in the line comprise the ThinkPad 755C and the ThinkPad 755Cs.^[5] As stock, the 755C and the 755Cs feature the i486 processor in its clock-doubled DX2 variant, with a clock speed of 50 MHz. Users could optionally upgrade the DX2 to the clock-tripled 75-MHz DX4. The 755C features a 10.4-inch, color, active-matrix TFT liquid-crystal display (LCD); while the 755Cs features a 9.5-inch, color, passive-matrix STN LCD. IBM offered the laptops with either a 340-MB or a 540-MB hard disk drive (HDD) and a 3.5-inch, 2.88-MB floppy disk drive.^[6]

The 755C and Cs models were internally strongly associated with the Thinkpad 750, sharing many of the internal components and therefore can be swapped between machines.^[7]

ThinkPad 755CE, 755CSE, 755CD

IBM followed up the original two models of the ThinkPad 755 with the ThinkPad 755CE, ThinkPad 755CSE, and the ThinkPad 755CD in October 1994.^[8][9] All three models of ThinkPad feature, as stock, the i486DX4 clocked at 100 MHz.^[8] On these three models, the i486DX4 is contained on a daughterboard that connects to a socket on the motherboard, allowing the laptop to receive aftermarket processor upgrades (see below).^[10]

The 755CD was the first notebook computer on the market with an internal, full-sized (120 mm diameter) CD-ROM drive.^[11][12][a] The CD-ROM drive was a double-speed, tray-loading model that plugged into the UltraBay underneath the keyboard. In order to accommodate the CD-ROM drive, IBM designed the 755CD to be 7.2 mm thicker than other models in the ThinkPad 755 range (including the 755CE and the 755CSE), for a total thickness of 57 millimetres (2.2 in).^[15][8] Customers could have purchased the internal CD-ROM separately and plugged it into an external UltraBay drive enclosure that plugged into a special plug on the side of the 755CE and the 755CSE; however, because of their thinner stature, they cannot house the CD-ROM internally.^[15]

The 755CE, the 755CSE, and the 755CD also replaced the sound chip by Crystal Semiconductor of prior 755 models with the Mwave, a digital signal processor designed in-house at IBM that doubled as a 14.4-Kbps data/fax modem, a speakerphone, and an answering machine.^[15] Additionally, the built-in TrackPoint pointing device of prior ThinkPads was improved to sport a rougher, grippier texture of the pointing stick, preventing the finger from easily slipping off during use, while the left- and right-click button switches were made heavier to prevent accidental actuation.^[15] The 755CE and the 755CD feature a 10.4-inch active-matrix TFT LCD with a special polarizer, dubbed "Black Matrix", which enhanced the picture's dynamic range. The 755CSE, on the other hand, shipped with a 10.4-inch passive matrix STN LCD.^[8] All three models of ThinkPad were optioned with either 340-MB, 540-MB, or 810-MB HDDs.^[8][9]

In September 1995, IBM began selling the 755CE, the 755CSE, and the 755CD with an optional processor daughtercard containing a Pentium processor clocked at 75 MHz. While its clock speed was technically slower than the i486DX4, the Pentium was quicker and more efficient.^[16]

The 755CE and all subsequent models were architecturally very different from the 755C and Cs models. Very little can be shared or swapped between models.^[17]

ThinkPad 755CDV, 755CV, 755CX

In June 1995, IBM refreshed the 755 line with three new models: the 755CDV, the 755CV, and the 755CX. The 755CDV and the 755CV feature 100-MHz i486DX4 processors, while the 755CX features the original Pentium processor clocked at 75 MHz. The 755CX was IBM's first laptop based on the Pentium processor.^[18][19]

The 755CDV and the 755CV meanwhile were designed with a specialized top housing that put the backlight of the 10.4-inch active-matrix TFT LCDs on a detachable tray, the removal of which makes the LCD transparent. Additionally, the laptop is able to be pivoted 180 degrees flat. These two design elements were intended for using the laptop on a commodity overhead projector to display its graphical output.^[20][21] This was an inexpensive and less cumbersome alternative to owning dedicated digital projectors that could take VGA input, a class of projector which did not go down appreciably in price and weight until years later.^[22][23] The convertible approach of the 755CV and 755CDV was not new to notebook computers: Revered Technology Inc. (RTI) had a similarly designed notebook, the Power Cruiser, on the market in 1994.^[22] Other companies had also been selling standalone transparent LCD panels for placing onto overhead projectors that could take input from a computer for some years.^[21]

The 755CDV came with the internal UltraBay CD-ROM of the 755CD preinstalled, while the 755CV and the 755CX lacked this option. However, all three models of ThinkPad were designed with the Mwave DSP on-board, like the 755CD.^[18][19] Around August 1995, IBM upgraded the 640-by-480-pixel VGA display of the 755CX to Super VGA, at 800 by 600 pixels.^[24][25] In September 1995, IBM began selling the 755CDV and the 755CV with the 75-MHz Pentium processor daughtercard as an option.^[16]

The 755CX is unique in how similar it is architecturally to the 760 successor machine.