By tradition the oldest style of opener. These slide up and down balanced by lead weights (in timber windows) connected to the sash by cords that run over a pulley wheel at the top of the window. The weights are stored in the side ‘boxes’ and also travel up and down to balance the sashes. Another name of course is ‘Sash box Windows’
The original windows were not very good as stopping draughts; wind could force itself around each side of the sash which by it’s very nature had to operate with a clearance between moving surfaces.
An alternate to weights and cords are springs. Springs take up less room which means that the side box can be reduced and the window can be fitted to the front brickwork line and still look appealing.
Spring balances are used in all plastic sash windows. This allows for a unique feature; each sash can tilt inwards for cleaning from the inside. The sash has supports that will hold it in position and can easily be pushed back after cleaning. I would suggest that larger windows are supported by a secondary means (a chair for example).
The Sash window is an expensive design to reproduce and although I have used the Aluminium double glazed vertical sliders in the past I believe the best products are made in Plastic, for their cost and appearance and the more expensive Timber option.