From my initial expenditure list, I knew that my laptop had to cost no more than $40, including shipping. As a result, my options were very limited. A cursory look at eBay told me I was going to have problems finding anything over a 100 MHz processor, much less be able to afford a color LCD screen or a CD-ROM. In addition, shipping costs added anywhere from $5–20 per order. So I stepped back and thought about what I really needed.
Assuming that my DPF would only have to load an OS and display images, my processing requirements weren't particularly demanding. I wanted at least a 486 processor, but according to the muLinux site, even an older 386SX might work. Converting this to actual processor speed means that I would want a 33–100 MHz processor, with a higher number being better.
RAM was a more significant problem. Most display programs, such as Windows 95 or even the X Window System (Linux) would require at least 8MB. While it's possible to load a GUI-based OS in less than 4MB of RAM, any graphics would be horribly slow and the chance of failure was very high. As a result, I figured that my laptop would need at least 8MB, with a preference of 16MB or more.
Nowadays, most people take hard disk space for granted. Unless you're downloading movies or MP3s, the standard 40–80GB is more than most people will use in a life time. However, space wasn't always this abundant. Even as few as eight years ago, hard drives had less capacity than the standard CD-ROM (600MB).
My picture viewer would be storing digital images locally on its drive. This requirement meant that I would need at least several hundred megabytes of space for storage. As I thought about the footprint of muLinux, in addition to its swap space, I concluded that 400MB should be more than enough space. My calculation was based on the assumption that anything over 2,000 pictures would be overkill. Given the fact that the pictures would have to be reduced to 640x480 (standard display for older laptops), each image should be no larger than 100KB. Doing the math, 2,000 pics × 100KB = 200,000KB (about 200MB). Assuming that each picture was displayed for one minute, it would take over 33 hours just to run through one cycle!
A digital picture frame wouldn't be very successful without a color LCD display. Fortunately, most laptops include at least some type of color support. The twist is that not all LCDs are the same. Available colors, quality, angle of view, and more can be affected by the LCD type. The following list outlines the terms/LCD types you need to be familiar with when looking for a DPF candidate:
- Active matrix. TFT LCDs use active-matrix technology, which uses 1–4 transistors to control each pixel on the screen.
- Passive matrix. Less costly than active-matrix types, this type of screen uses a grid of wires to display colors.
- TFT. The most common, but also the most expensive. The term TFT is often used interchangeably with active matrix.
- DSTN. This type of passive-matrix screen is relatively cheap to create and is found in low-end laptops. Generally, this type of screen supports fewer colors than TFT LCDs.
- VGA and SVGA. The video graphics array (VGA) defines the resolution of the display and the number of supported colors. VGA typically supports only 16 colors at 640x480, whereas super VGA (SVGA) can support a much larger resolution/color pool, as defined by the amount of video memory and screen type.
As you can see, selecting a laptop screen is not a simple process. Be sure to check the specifications of the desired laptop before making a purchase. For the most part, 65,536 is more than enough colors for a DPF. In addition, it's important to note that muLinux supports monochrome, VGA, and SVGA output. The inclusion of SVGA drivers with the NS1 package is one of the key reasons that muLinux attracted my attention. Without it, the images would be stuck at 16 colors.
While the exact visual design was still up in the air, I could expect that I would need some paint, Velcro, and some sort of frame. However, before purchasing any of these items, I would need to have the laptop in hand and working.
In summary, I was looking for a laptop with at least a 33 MHz processor, 400MB of disk space, 8MB of RAM, and a color screen. A CD-ROM would be nice, but not necessary. I was once again ready to start looking on eBay for a laptop.