The PB-100 represents Casio's step towards "real" pocket computers. While its
ancestor, the FX-702P, was still called "Programmable Calculator",
the PB-100 proudly bears the title "Personal Computer".
However, the PB-100 seems to have been a true low-cost design. Its
specifications are clearly inferior to those of its predecessor, the FX-702P, as
well as to SHARP's earlier pockets. The limited 12 character display makes BASIC programming and debugging a painstaking endeavor.
In its standard version, it is equipped with 1 KB of RAM which results in only 544 bytes for BASIC, which is really limiting. At least, with the memory module OR-1, it can be upgraded to 1568 bytes of user memory, so it begins to make sense that BASIC memory can be subdivided into 10 independent program areas P0-P9.
Moreover, the keyboard had been reduced to the absolute minimum; at any rate, it provided a QWERTY style layout (the FX-702P had a non-standard alphabetical layout).
On the other hand, the cute little machine is really small and lightweight, a
real pocket device.
The main circuits of the PB-100 are basically made up of two chips. Processor
logics, ROM, display driver, and keyboard controller are integrated in a single
CMOS VLSI chip HD61913, which has an external 4-bit bus. The second main
component is a HD61914, which is a 8192-bit static RAM organized as 2048 words
by 4 bits.
In 1983, the PB-100 was also released by Tandy Radio Shack as TRS-80
PC-4 and by Olympia as OP-544.
Thanks to Roman von Wartburg (retrocomputing.ch) for this information.
PB-100 vs mainframe by Richard Chequer:
I have a Casio PB-100 (with the optional OR-1 memory) which I have owned and used since 1983.
I have shadowed mainframe programs (pension calculations) using the PB-100. A work colleague would code the mainframe solution and I would do the equivalent with the Casio: if the answers agreed, the mainframe code was deemed correct.
The limitations of the display do mean that you have to write any potential program out on paper prior to typing it in. I have not had many problems with the limited memory: it is not designed for running large programs.
The only limitation in the code is that there is no "ELSE" construct on IF statements. This did not limit the programming, but the coding required was less elegant and compact than if this construct was implemented.
I still use the machine today and I consider it to be much easier to use than a programmable calculator. In terms of maintenance it has only required new batteries - and not too many of those, either!