Model 50 with Reply Board
The regular IBM PS/2 Model 50 was equipped with an 80286 CPU operating at 10MHz paired with 1MB of RAM and a 20 or 30MB hard disk. This configuration ended up being unsatisfactory to many who bought the machine due to slow hard disk access times compared to other machines and lack of features in general. IBM did two things to solve these problems: they introduced an upgrade hard disk controller board that let the Model 50 take advantage of much larger and faster hard disks and they also released a separate machine called the 50Z that had the much faster hard disk and much faster memory access.
From what I've heard, many folks found IBM's solutions to the 50's shortcomings to be rather expensive or out of the question entirely. There was another option, however, that extended the life of the machine considerably. It was known as the Reply board. There were two of these boards--the PowerBoard and the TurboBoard. The PowerBoard was the much more powerful of the two, but even the TurboBoard offered a vast improvement over a stock Model 50(z). The computer pictured is equipped with the Reply TurboBoard.
The Reply board was a drop in replacement for your existing Model 50 and once you installed it, you got a much faster processor (in the TurboBoard's case, you got an IBM 486SLC2 at 50MHz clock speed) more memory (up to 16MB for the TurboBoard), better video (a Cirrus Logic SVGA chipset) and the ability to use your existing hard disk or to upgrade to an IDE hard disk--or even do both!
Though already the Model 50 is a useful machine without the Reply board, I find it nice to have the additional CPU speed, more memory and better video. Also, the Reply board opens major doors as to the choice of operating system you can use.