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Thread: IBM 5155 vs. Compaq Portable, info discrepancy

  1. #1

    Default IBM 5155 vs. Compaq Portable, info discrepancy

    I've been trying to find information comparing the IBM 5155 Portable PC and the Compaq Portable, out of personal interest, and it's kind of frustrating because I'm finding a lot of contradicting information.

    The biggest one I find is regarding the price of the machines. Lots of web pages about the 5155 talk about it's "lower price tag" compared to Compaq's machine, yet as far as I can tell the 5155 was more expensive at $4225, compared to Compaq's $3590 (both configured with two disk drives).

    Another regards the software compatibility. Some websites say the Compaq was 100% IBM compatible, while others say it was "95% at best". In fact, I recall reading, a long time ago, that the 5155 itself wasn't 100% IBM compatible, because of the way the video card addressed the internal display, or something like that. However, I can't find that claim anywhere now.

    Does anyone know enough about both machines to clear these up?

  2. #2
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    There were software incompatibilities with the Compaq Portable - primarily applications that expected Cassette BASIC to be in ROM, which for obvious licensing reasons, didn't happen on any clone.

    The 5155 is an XT - it's not even 100% compatible, it just is an XT, same exact motherboard. The video card is a standard CGA card, and the internal composite output is what's used by the internal display. No need to address it, as all outputs (RGBI, external composite, and internal composite) are active at all times (and in fact, the internal and external composite are wired together - if you plug a TV into it, you'll notice that the internal video dims due to two things being connected to the same hardware and loading things up more).

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    Keep in mind that the earliest reviews would likely be more critical of compatibility as third party software had not yet had a chance to adapt. The Compaq Portables were wildly successful compared to other early clones, and most software vendors quickly added official support (not that they had to do much for it).

    Over time, there were also updates to the Compaq Portable's BIOS ROM that supposedly improved compatibly. Unfortunately, I am not aware that anyone has dumped the earlier Compaq Portable BIOS ROM revisions for comparison.

    As stated, the lack of ROM basic (and in some cases, simply by not being the IBM BIOS ROM) would cause software compatiblity issues. But this was only a problem for a few titles, and as it became apparent this would be the case on all clones, new software quickly stopped requiring that.

    The IBM 5155 was literally an XT 5160 stuffed in to a portable case. As such, there were no software or hardware compatiblity differences between those. Compared to the original 5150, they were already very compatible, with only minor differences.

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    You might want to add the Portable Plus to your comparison, as that machine is closer to the XT than the PC. For example, the Plus BIOS allows 640k on the motherboard.

    ...I'm also wondering what a extras a 5155 came with in the base configuration. A Portable (and the Plus) included a parallel port on the floppy controller, but no serial port. Did the 5155 come with any ports, besides the external floppy port?

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    Quote Originally Posted by Casey View Post
    You might want to add the Portable Plus to your comparison, as that machine is closer to the XT than the PC. For example, the Plus BIOS allows 640k on the motherboard.

    ...I'm also wondering what a extras a 5155 came with in the base configuration. A Portable (and the Plus) included a parallel port on the floppy controller, but no serial port. Did the 5155 come with any ports, besides the external floppy port?
    The default 5155 setup had both parallel and serial ports on separate short cards in addition to the floppy controller and CGA card.

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    Quote Originally Posted by Casey View Post
    You might want to add the Portable Plus to your comparison, as that machine is closer to the XT than the PC. For example, the Plus BIOS allows 640k on the motherboard.
    The Compaq Portable and Compaq Portable Plus are actually completely identical machines other than the Plus includes a hard drive. Later revisions of the motherboards supported more RAM, but otherwise did not seem radically different. They went through a number of motherboard revisions, but it seems that these are not currently as well documented as IBM's.

    The Plus I happen to have does not support extra ram on the motherboard, and even has the unpopulated area that is allegedly for cassette interface circuitry. I recall reading that there was an upgrade PAL that would also enable support for 640k on board.

  7. #7

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    Compaq had better marketing and the Portable had been on the market for two years before IBM came up with their competitor. The IBM 5155 had a better keyboard and unquestioned compatibility, but the Compaq had a high-res EGA-quality text mode, versus the 5155's grainy CGA text. The 5155 did have a problem with some color combinations causing illegible text, but that's the same problem that any other PC with a monochrome composite monitor would have, and can be resolved in most cases by typing MODE BW80 in DOS or by choosing the application's monochrome option.

    I'm not sure how the prices of the IBM and Compaq compared, but I do believe that IBM cut the prices of both the 5155 and PCjr shortly before discontinuing them, in an attempt to boost their lagging sales figures. Also some reviewers said that IBM should've called the 5155 the "Portable XT" instead of the "Portable PC" because many people thought it was based on the 5-slot 5150 PC rather than the 8-slot XT motherboard.

    p.s. I've heard that the original Compaq Portable had a pinout on its motherboard for a cassette port, but it was never implemented.


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    Quote Originally Posted by Casey View Post
    ...I'm also wondering what a extras a 5155 came with in the base configuration. A Portable (and the Plus) included a parallel port on the floppy controller, but no serial port. Did the 5155 come with any ports, besides the external floppy port?
    Quote Originally Posted by krebizfan View Post
    The default 5155 setup had both parallel and serial ports on separate short cards in addition to the floppy controller and CGA card.
    According to IBM's product announcement document, at [here], serial ports and parallel ports were "Optional Features".

    This is supported by photos of the 5155 that PC Magazine used for review (MAY 1984 edition). The photos show only two cards, the CGA and the floppy controller.

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    It had a different BIOS. I think. I had one back in the day (they were still using the full-height Tandon-style drives for this model), and paid for an upgrade from 256k on the motherboard to 640k. Watched the tech go through the whole process, and he answered my (many) questions. Unless he was BS'ing me about the BIOS upgrade. I do know he swapped out a socketed chip which allowed the upgrade. He said it was a new BIOS.

    I've been told also that the Plus had a stronger power supply ~150 watts for a hard drive.

  10. #10
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    AFAIK, the early Portable BIOSes were cloning the early PC BIOSes - that is, the ones that couldn't actually use option ROMs.

    So, there may well have been a BIOS upgrade to add that support, that the Plus also got.

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