PowerBook 100 & 170 owners

JDW · Nov 9, 2025

PowerBook 100 & 170 owners, could you please measure the displayable PIXEL AREA of your LCD from the bottom left to the top right? (Not the visible LCD area, but the displayed pixel area.) To accomplish that, launch Photoshop 1, full the screen with black and make it full screen.

Feel free to tell me that diagonal screen measurement in millimeters if you lack an inch ruler.

I measured my Macintosh Portable 5126 LCD's displayable pixel area to be 9.76" diagonal, so at 640x400, that yields 77dpi. I want to compile the same info for those two PowerBooks, but I don't have the 100 or the 170 to measure myself.

My guess is the PB170's LCD should match my 5126 because both LCDs are from Hosiden. The PB100 might be different though because that panel was made by Sharp.

Thank you!

T-Man · 2025-12-01T10:20:49+0000

Well; on 170 have Superpaint 1.1, MacDraw and MacPaint if there is a way to obtain the information there. Superpaint 1.1 does have an option to measure in "screen dots" but no option for full screen. . Will see if I have disks somewhere to see if I can install photoshop.

T-Man · 2025-12-01T10:34:09+0000

How about this....in the Superpaint 1.1 available window I can see, the ruler when set to "screen dots" is 575 horizontal and and about 19.5 cm when ruler set to cm, 7 and 11/16 inches and 47 when set to "pica/points"
Vertically 720 when set to "screen dots", 24.4 cm, 9 and 5/8 inches or 57.5 when set to "pica/points".

that is to say the above are the same screen window only changing units on the preferences plane.

JDW · 2025-12-01T11:25:57+0000

Thank you for replying, but I need to clarify when you mean in your second post.

What is "575"?
You measured 19.5cm diagonally with a ruler or measuring tape, using an all-black screen, from the very bottom left corner to the top right corner?

I'm rather confused by what 24.4cm means because it seems like you measured the vertical height there, but your "width?" is 19.5cm?

All we need is the diagonal measurement. I then dump that into ChatGPT and instruct it to calculate the DPI from that single measurement.

T-Man · 2025-12-01T13:56:11+0000

All of the above are measurements with the on screen ruler just with different units using SuperPaint 1.1, I cannot find any command for full screen as per your Photoshop description; good news though, found a photoshop 3.0 that should install, but on CD so now will need to find cable and drive.....maybe able to attempt later today and give exact info as per your original request

JDW · 2025-12-01T14:00:48+0000

Steps to Success with Photoshop 1.x

1. Launch the app.
2. CMD-N
3. Set your screen's native resolution (640x400) and click Gray Scale and then OK
4. Choose the Paint Bucket Tool and fill the window with Black.
5. Look at the very bottom of the toolbar at left, and click the rightmost icon of the three to fill your screen with black.
6. Press TAB to eliminate the toolbar at left.
7. Now physically measure diagonally with a measuring tape. (I use a body measuring tape because it's the easiest and soft too so it won't scratch your screen.)

DONE!

joevt · 2025-12-01T23:46:26+0000

JDW said:
All we need is the diagonal measurement. I then dump that into ChatGPT and instruct it to calculate the DPI from that single measurement.

The vertical and horizontal resolution also needs to be known to calculate the DPI, but this info can be gathered from the Mac's specs.

Alternatively, you can also just use the horizontal number of pixels and width or just use the vertical number of pixels and height. Using the diagonal is preferable because it is longer than the width and height which reduces the error in the DPI calculation.

DPI is pixels / inches. There is 1 inch / 25.4 mm.

DPI = 640 / width in inches
DPI = 400 / height in inches
DPI = sqrt(640^2 + 400^2) / diagonal length in inches

DPI should be the same for all three calculations if the pixels are square (the default for all Macs) and the lengths are accurate.

If you measure a diagonal of 266 mm on a 640x400 display then the result is ≈ 72 dpi.

Code:

bc <<< 'scale=10; sqrt(640^2 + 400^2)/(266/25.4)'
72.0671039867

An onscreen ruler probably assumes 72 dpi unless you change the document preferences to use a different resolution (for example, 300 dpi for a printer).
Portables usually have smaller pixels which means they usually have more than 72 dpi?

T-Man · 2025-12-02T00:08:06+0000

installed photoshop 2....i cannot find a full screen option; the viewable diagonal on finder is 9 and 7/8 inches. heigh 5 and 2/8ths; width 8 and 4/8ths; inclusive of menu bar.

JDW · 2025-12-02T00:24:39+0000

@T-Man & @joevt
ChatGPT is faster than using a calculator when you already have the basic template, which I filled out using the measured data of the previous post as follows:

Monochrome LCD screen with square pixels.
Resolution: 640x480 pixels
Height: 5 2/8"
Width: 8 4/8"
Diagonal: 9 7/8"
Calculate DPI. Don't show work. Give me the number only.

ChatGPT: 81

Interestingly, 81DPI is the same exact number I had guesstimated previously and wrote into my Spreadsheet here:

Macintosh Portable Specifications

docs.google.com

I measured my 5126 Mac Portable's screen myself, so I know it is 77dpi. I got a 76dpi for the PB170 based on measurements given to me by a PB170 owner on FaceBook. I think I did with the 140 too, although I've forgotten. The only unknown is if the PB100 display is 9.8" or slightly different. My aim in gather measurements is to get a more precise set of info, rather than "marketing lies." For example, marketing departments could call a 9.76" display 10" inches for simplicity's sake. I personally don't like simplicity.

Thank you for the measurements!

joevt · 2025-12-02T05:09:33+0000

T-Man said:
installed photoshop 2....i cannot find a full screen option; the viewable diagonal on finder is 9 and 7/8 inches. heigh 5 and 2/8ths; width 8 and 4/8ths; inclusive of menu bar.

The error may be up to less than an 1/8 of an inch which is not bad since you are measuring in eighths of an inch.

Code:

bc <<< 'scale=10; (sqrt((5+2/8)^2 + (8+4/8)^2) - (9+7/8))*8'
.9249648104

Remind me, do 68K portables have square corners or round corners? Round corners make it difficult to measure the diagonal.

Measuring the horizontal and vertical would have the same problem at the edges if the corners are round. Away from the corners, you have the problem of ensuring that the distance measured is perfectly perpendicular to the edges (the minimum distance between edges).

If the corners are square, then a solid desktop background color should do just as well as a full screen image in Photoshop.

JDW said:
Monochrome LCD screen with square pixels.
Resolution: 640x480 pixels
Height: 5 2/8"
Width: 8 4/8"
Diagonal: 9 7/8"

The PowerBook 170 has a resolution of 640x400 so the DPI is between 75 and 77.
The diagonal might be the most accurate because it is the longest dimension, so 75.5.
Rounding this would give 76 which is what your spreadsheet has.

Code:

bc <<< 'scale=10; sqrt(640^2 + 400^2) / sqrt((5+2/8)^2 + (8+4/8)^2)'
bc <<< 'scale=10; 640 / (8+4/8)'
bc <<< 'scale=10; 400 / (5+2/8)'
75.5427035700
75.2941176470
76.1904761904

JDW · 2025-12-02T05:19:40+0000

I cannot speak as broadly as "all 68K Portables," but the first trio of MONOCHROME PowerBooks were square corners.

David Cook · 2025-12-02T09:02:24+0000

JDW said:
Monochrome LCD screen with square pixels.
Resolution: 640x480 pixels
Height: 5 2/8"
Width: 8 4/8"
Diagonal: 9 7/8"
Calculate DPI. Don't show work. Give me the number only.

I'm not sure which laptop the above measurements apply to. I just hand measured and got:

Backlit portable: 21.1 mm x 13.1 mm = 5.157 in x 9.778 in = 9.78 in diag = 77 dpi
PowerBook 100: 19.15 mm x 12 mm = 7.54 in x 4.72 in = 8.9 in diag = 84.8 dpi

joevt · 2025-12-02T09:15:21+0000

David Cook said:
I'm not sure which laptop the above measurements apply to. I just hand measured and got:

Backlit portable: 21.1 mm x 13.1 mm = 5.157 in x 9.778 in = 9.78 in diag = 77 dpi

I think you mean 21.1 cm x 13.1 cm = 8.307 in x 5.157 in = 9.778 in diag = 77.2 dpi

David Cook said:
PowerBook 100: 19.15 mm x 12 mm = 7.54 in x 4.72 in = 8.9 in diag = 84.8 dpi

cm instead of mm.

David Cook · 2025-12-02T09:24:48+0000

Here are a couple of technical tidbits for you...

The Macintosh 128 & 512 had 20 bytes of PRAM.
The Plus, Mac II, SE, SE/30, IIx, and IIcx bumped that up to 256 bytes of PRAM.
The Portable shipped after all of those, but only had 128 bytes of PRAM. Worse still, Apple did not allocate the bytes contiguously (i.e. it is not the first 128 bytes of PRAM) and if you ask for anything not available the entire call fails. So, many tech tools (like TattleTech) can't display raw PRAM data on a Portable.

The Backlit Portable allows RAM expansion in the RAM slot or the PDS slot. However, if you install a third-party PDS RAM card alongside an Apple RAM card, you'll max out at 4 MB. https://www.savagetaylor.com/TIL/TIL07300.pdf I bought a portable an eBay with both cards. It showed 4 MB of RAM. Pulling the Apple card caused memory to jump to 7 MB. I feel sorry for whoever bought the second card back then and thought they were getting a boost.

David Cook · 2025-12-02T09:25:25+0000

joevt said:
I think you mean 21.1 cm x 13.1 cm = 8.307 in x 5.157 in = 9.778 in diag = 77.2 dpi

cm instead of mm.

Yup. It's late. : )

JDW · 2025-12-02T09:26:19+0000

77 DPI for the Mac Portable is expected and matches my Spreadsheet value.

But the 84.8 DPI for the PB100 is at odds with the 81 DPI calculated from the measurements of @T-Man .

I personally prefer metric measuring devices, unless the ruler or measuring tape in inches has super fine divisions. David seems to have measured with a metric measuring tool.

However, I made a blunder with ChatGPT because I previously fed it 640x480 by accident. Resolution is only 640x400! So with that change alone, the measurements of @T-Man result in a 76.2 DPI value, which cannot be right because the PB100 has higher resolution than the PB140/170 and Mac Portable.

Holy cow. I also see @T-Man measured the PB170 and in my brain I was thinking PB100, so I totally messed it all up!

I think I will go with your numbers, @David Cook ! I just now updated my spreadsheet.

David Cook · 2025-12-02T09:28:45+0000

JDW said:
t in a 76.2 DPI value, which cannot be right.

I placed a piece of transparency over the screen and marked the corners. I then pulled it off and measured it with a ruler. I am confident in those values (after correcting for mm -> cm)

JDW · 2025-12-02T09:31:24+0000

Thank you both for measuring! The spreadsheet is now perfect, I think!

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