This guide documents the process of creating a bootable compact flash card for the IBM PCjr. Using a CF card as a hard drive replacement provides reliable, silent storage for your vintage PCjr.
Requirements
- 40-pin IDE to Compact Flash adapter (not 44-pin!)
- Compact Flash card (I used a 15GB SanDisk II)
- DOS 3.3 boot floppy disks
- Power connection for the adapter
Important: Make sure you get a 40-pin IDE adapter, not a 44-pin. Lesson learned the hard way. These are available on eBay for around $6.
Hardware Setup
- Connect the 40-pin IDE to CF adapter to your PCjr’s IDE interface
- Hook up power to the adapter
- Insert your compact flash card
- Note: The adapter goes together opposite of what you’d expect - don’t worry if you get it backward the first time, everyone does
Wiping the Partition Table
Before you can partition the CF card, you need to wipe
any existing partition table. This is surprisingly hard
to do with standard utilities - PC fdisk won’t do it,
and Mac Disk Utility won’t without creating a new partition.
The solution is a short assembly program entered via the
DOS debug command:
- Boot from DOS 3.3 Floppy Disk #1
- Switch to DOS 3.3 Floppy Disk #2 (contains
debug) - Enter the following:
A> debug
a
mov ax, 309
mov cx, 1
mov dx, 80
int 13
int 20
g
When you type a to assemble, debug will show memory
addresses before each line - just type the instructions
as shown. Press Enter on a blank line when done, then
type g to execute. This wipes the partition table.
Creating the DOS Partition
- Reboot and boot from DOS 3.3 Floppy #1 again
- Run
fdiskand create a primary DOS partition - Reboot again (fdisk requires this)
Formatting and Installing DOS
- Format the CF card and install the boot sector:
A> format C: /s
This formats the card and installs the boot loader and
command.com.
- Copy the DOS utilities to the hard disk:
A> copy a:*.* C:
- Remove the floppy and reboot - your PCjr should now boot from the compact flash card!
Writing Disk Images to Floppy
If you need to write disk images to floppy disks:
C:> format A:
C:> diskimage disk.img 0:40:2:9
Notes
Part of the fun of these vintage computers is the journey. But to be honest, sometimes you’re just not sure you’re going to get there. Persistence pays off!