Punch cards

Anyone know what are these ? Greeting cards ? No. These are punch card. They serves as input instruction into a computer in 70s ~ 80s. Program are developed using Frotran 77 programming language. Each card contain one instruction. The instruction punch some holes in the card and the card flow through a card reader where there is light and sensor to read the card. A hole where light socuce can go through represent a Logic 1 and no hole represent Logic 0 simulating switching ON and Switching OFF. In order to make the program work , there are many instructions and hence many cards. The sequence of these card is essential as it determine how a program is to be executed. So to Sabo someone whom you don't like , just rearrage his punch cards and his program will hang ! Some genius student use these card to generate patterns and hecne we have these nice looking punch cards. Many student duplicating these punch cards with pattern causing the punching machine to jam and malfunction and were warned by the Staff. The small rectangular holes from these cards are often collected by student and use for JAM. Those where the years in 80s in NUS.