
Sharp PC-E500S

The Sharp PC-E500S was a 1995 pocket computer by Sharp Corporation and was the successor to the 1989 PC-E500 model, featuring a 2.304 MHz CMOS CPU.
Description.
It was slightly wider, and the keys are slightly larger than the previous model. The display had more contrast, and the keyboard cover is a (removable) hinged lid (clamshell) instead of plastic slipcase. There were also four additional BASIC commands. Programs written on PC-E500 were executable on the PC-E500S.
It came with 32 KB of RAM which could be upgraded to 96 KB using memory expansion cards. The monochrome LCD had 240×32 pixels which could display four lines with 40 characters per line as well as graphics. The 256 KB system ROM the contained the BIOS, a diagnostic suite, and the BASIC interpreter used to program the device. 
An algebraic calculation system was included. The Algebraic Expression Reserve (AER) memory: Frequently used formulas or constants could be stored in memory and recalled for repeated use. The PC-E500 series also performed as a scientific calculator when switched into 'CAL' mode.
It also included an X<>Y exchange key for working with complex numbers and polar to rectangular conversions.
Applications.
In addition things like amino acids and the periodic table of elements were available. These built-in programs were accessed through a menu system and special function keys. There was also a built-in menu editor to add new software to the menus or indeed replace some built-in software or formulas.
Memory expansion.
The Sharp PC-E500 series could store data and programs on memory expansion cards as well as the main RAM. Six cards were available:
These cards used a CR1616 lithium battery for memory backup.
The memory configuration was software-switchable from the command-line. The RAM card could be appended to the system memory, replace the system memory or act as a separate space to be used as a RAM drive (F:). The main memory could also be partitioned off to a RAM drive (E:).
Peripherals.
The PC-E500S had a weight of 340 g (with batteries) and was powered by four AAA batteries. It could, given its power consumption of 0.09 W, be used for about 70 hours on a charge.