The newer 80 connector cables (the one with thinner cables) contains just that- 80 connectors. Between every data line, there is a thin line going no where- this is a ground wire. Its purpuse is simple- when electricity flows through a cable, it emits an electrical field around that said cable. This field can alter the field of other cables, or flat out cause a current to flow through anoth wire (Some amplifiers work in thsi manner). Hwn moving data at high speeds, it si common for these electrical/magnetic fields to alter and distort the data of surrounding cables. To remedy this , a ground cable is placed inbetween to act as a buffer and increase data performance at ATA100/133 speeds.
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