Bitcoins growing popularity is having other ripple effects. Every participant in the system must keep a copy of the block chain, which now exceeds 11 gigabytes in size and continues to grow steadily. This alone deters casual use. Bitcoins designer proposed a method of pruning the chain to include only unspent amounts, but it has not been implemented.
As the rate of transactions increases, squeezing all financial activity into the preset size limit for each block has started to become problematic. The protocol may need to be tweaked to allow more transactions per block, among other changes. A further problem relates to the volunteer machines, or nodes, that allow Bitcoin to function. These nodes relay transactions and transmit updates to the block chain. But, says Matthew Green, a security researcher at Johns Hopkins University, the ecosystem provides no compensation for maintaining these nodesonly for mining. The rising cost of operating nodes could jeopardise Bitcoins ability to scale.