With microprocessors now ubiquitous, the computers inside modern slot machines allow manufacturers to assign a different probability to every symbol on every reel. To the player it might appear that a winning symbol was 'so close', whereas in fact the probability is much lower.

In modern slot machines, the reels and lever are for historical and entertainment reasons only.

The video slot machine is a more recent innovation, with no moving parts at all – instead a graphical representation of one appears on screen. Since the player is essentially playing a computer game, the manufacturers are able to offer more interactive elements, such as advanced bonus games and advanced video graphics.

In addition, because there are no mechanical constraints on the design of video slot machines, most display five reels rather than three. This greatly expands the number of possibilities: a machine can have 50 or more symbols on a reel, giving odds as high as 300 million to 1 against – enough for even the largest jackpot. As there are so many combinations given by five reels, the manufacturers do not need to weight the payout symbols (although some may still do so). Instead, higher paying symbols will typically appear only once or twice on each reel, while more common symbols, earning a more frequent payout, will appear many times.

Video slot machines typically encourage the player to play multiple 'lines', so rather than simply taking the middle of the three symbols displayed on each reel, a line could go from top left to bottom right, or any of the other patterns specified by the manufacturer. As each symbol is equally likely, there is no difficulty for the manufacturer in allowing the player to take any or all of the possible lines on offer – the long-term return to player will be the same. The difference for the player is that the more lines he plays the more likely he is to get paid on a given spin – though of course he is betting more in the first place.

To avoid the feeling that the player's money is simply ebbing away (whereas a payout of 100 credits on a single line machine would be 100 bets, and the player would feel they had made a substantial win, on a 20 line machine, it would only be 5 bets and would not seem significant), manufacturers commonly offer bonus games, which can return many times their bet. The player is encouraged to keep playing to reach the bonus: even if he is losing, the bonus game could allow him to win back his losses.