Here's a detailed glimpse of many of the older video game systems and their features and capabilities.  This guide will cover 8 bit and 16 bit systems and I’ll be writing subsequent guides for the 32 bit and next generation systems.
I hope this if useful!

The 8 Bit era
System Name:  Nintendo Entertainment System (NES)
Company:  Nintendo
Released:  Mid 1980’s
Format:  Cartridge
Tech Specs:  8 bit
   RF output
   Mono AV output located on side of system
   2 Controller Ports (upgradeable to 4 with external adapter)
   Power and Reset buttons
Controllers:  D-pad, select, start, A, B, buttons
Japanese version: Famicom
Other versions: Late in its life cycle Nintendo released a redesigned, smaller more compact version of the system.  It featured a top loading interface and redesigned controllers.
Funky add-ons: Power Glove, U Force, Powerpad
Quirky Fact:  Early runs of some Nintendo NES games in North America contained a built-in adapter to allow you to play Famicom games on your NES.  Rumour was that Nintendo was short on supply and went with an interim solution and used the famicom boards for a short period.

System Name:  Sega Master System
Company:  Sega
Released:  Mid 1980’s
Format:  Cartridge/Card
Tech Specs:  8 bit
   RF output
   Mono AV output located on side of system
   2 Controller Ports (upgradeable to 4 with external adapter)
   Power and Reset buttons
Controllers:  D-pad, A, B, buttons
Japanese version: Sega Master System
Other vesions: Much like Nintendo Sega released a smaller, more compact version of the Master System
Funky Add-ons: Light Gun, Joystick
Quirky Fact: Some Sega Master systems came with a built-in game right in the console itself.

The 16 Bit era

System Name:  Super Nintendo (NES)
Company:  Nintendo
Released:  Early 1990’s
Format:  Cartridge
Tech Specs:  16 bit
   RF output
   Sterio Multi-AV output located on rear of system
   2 Controller Ports (upgradeable to 4 with external adapter)
   Power, eject, and Reset buttons
Controllers:  D-pad, select, start, A, B,X,Y, and L,R buttons
Japanese version: Super Famicom
Other versions: Late in its life cycle Nintendo released a redesigned, smaller more compact version of the system.  It no longer had the eject lever and only had a multi AV port for the TV signal. The Power and Reset buttons were redesigned.
Funky add-ons: Super Scope, Miracle Piano Teacher
Quirky Fact: The Super Nintendo was to release a CD add-on accessory with technology provided by Sony.  Apparently the deal went sour and Sony ultimately ended up releasing a stand alone CD system know as the Sony Playstation.

System Name:  Sega Genesis
Company:  Sega
Released:  Early 1990’s
Format:  Cartridge
Tech Specs:  16 bit
   RF output
   Sterio Multi-AV output located on rear of system
   2 Controller Ports (upgradeable to 4 with external adapter)
   Power, volume control, and Reset buttons
Controllers:  D-pad, select, start, A, B, C buttons
Japanese version: Mega Drive
Other versions: Sega was notorious for releasing add-ons and other versions of the system.  There are three versions of the Sega Genesis in total: The first system had a white reset button, a volume control switch for optional headphone support, and a power switch that toggled between on and off.  The Genesis II system was more compact in design, square rather than rectangular, and featured new RF and AV inputs, along with push button start and reset buttons.  The third Genesis system which debuted very late in its lifespan was the most compact design of the three.  Sega also released six-button control pads later on along with a host of other system upgrades which I’ll cover below.
Funky add-ons: Sega CD – first debuted as a front loading system designed for the Sega Genesis one system.  It offered CD quality sound and interactive gameplay with live video footage.  The Sega CD had a second version which was a side-by-side unit, top loading, and was compatible with both Sega Genesis I and II systems.  Finally, Sega released the 32X adapter which was an add on unit that promised to offer 32-bit graphics. Did it accomplish what it set out to do?  Well, not really.  Then there was the Power Base Converter which allowed one to play Sega Master System cartridges and cards on the Sega Genesis I system.
Quirky Fact: The console wars really began when Sega and Nintendo competed for dominance in the gaming world.  The market was never better as it was during the 16-bit wars.  Sega looked as if it was going to take over the market however Nintendo managed to pull through and is still producing consoles to this day whereas Sega is now only publishing games.

System Name:  Turbo Grafx 16
Company:  NEC
Released:  Early 1990’s
Format:  Hu Card
Tech Specs:  16 bit
   RF output
   1 Controller Ports (upgradeable to 6 with external adapter)
   Power, buttons
Controllers:  D-pad, select, run, I and II buttons
Japanese version: PC Engine, Core Grafx, Duo R, Duo RX, Shuttle
Other versions: NEC released a Super CD add-on accessory that attached to the rear of the system and was a top loading unit. Later, the elite Turbo Duo console was released which featured a side by side setup with Hu Card and top-loading CD Support all in one unit.  The control pads of the Duo were not compatible with the TurboGrafx and vice versa.  The Duo still fetches upwards of $500 on eBay.
Funky add-ons: 
Quirky Fact: NEC had a fantastic system on their hands but weren’t able to keep up with the big marketing dollars and install base of the Sega and Nintendo systems.