This is the Texas Instruments TI-86 Graphing Calculator. Add to this the ability to write highly complex programs to perform long, repetitive tasks, and a storage memory rivaling the capacity of early computers, and you have the TI-86. Indeed, the 86 is better described as a handheld computer than a calculator. Earlier computers that took up entire buildings had far less computational musclepower than the TI-86, and they sucked down hundreds of kilowatts of power, when they weren't shut down due to component failure. The TI-86 only uses 6 volts of electricity, lasting for months on 4 little AAA batteries, and is extremely rugged.
Some people tweak the hardware on their calcs a bit.
Some 86's have custom installed switches to change the speed, some have speakers built in, different LCDs, or double linkports.