Targeted mostly at computers without floppy drives (the lowest-priced 5150 sold with 16KB of RAM and no drives), this version of BASIC could save programs only to cassette tapes.
You read that right: Like other personal computers of the era, the 5150 came equipped with a cassette port on the back.
With the appropriate cable, users could save and load programs from a standard Philips compact cassette tape. The tech was slow and poorly implemented on the PC, but cassette players (and tapes) were orders of magnitude cheaper than floppy drives in 1981.
Stuck in 40 Columns
Once I booted into BASIC, I noticed that the machine's display was stuck in 40-column mode (that is, capable of showing only 40 columns of letters on the screen at once). As a business machine, the 5150 supported an 80-column display. Switching it was possible, but I didn't remember how.
Instead of a software-based BIOS, IBM equipped the 5150 with a series of dip switches on the motherboard for configuring basic system parameters, such as what kind of video card you're using, how much RAM the system has, and how many floppy drives are installed. I saw that all the dip switches on this PC's motherboard were set correctly for 80-column CGA, so I was stumped.
Next I booted into PC DOS 3.3 (PC DOS is what IBM called its version of MS-DOS) off a floppy disk. Still 40 columns. Then I remembered that there was some way to change the video mode in DOS. I thumbed through an authentic PC DOS 3.3 paper manual to find the solution: A DOS command called "MODE" sets the video mode. The mode I needed was called "CG80," which set up a color, 80-column mode in DOS. Yes, 80 columns at last!
Somewhere along the way, I decided to add a second 360KB floppy drive to make my journey easier. Thinking ahead, I had brought a half-height unit (pulled from another PC years ago) along from my house the day before. Doing serious work on a single-floppy-drive machine involves a lot of disk swapping, which is never fun.
Next page: Resolving software issues and viewing graphics
Day 3: Getting Down to Business
Day 3 started with me rifling through my garage, looking for a 4164C RAM chip to replace the bad one in the 5150. Fortunately, I found a host of them in an ITT Xtra, a 1984 IBM PC XT clone.
Once safely in my remote isolation bunker, I opened the 5150 again and swapped out the bad RAM chip for a good one. Success! Everything was now in complete working order.
The Software Problem