Psychology 9-1 GCSE - 

2.1.2 - Understand the features of short-term and long-term memory, including:

a) Duration - 

STM (short term memory) - Duration of information held in short term memory seems to be between 15 and 30 seconds, but the duration you can hold it here depends on the type of information it is. STM holds primarily acoustic encoded memories (sound). 

LTM (long term memory) - Duration of information held in long term memory is thought to be infinite, but you can often only keep accessing it if you frequently retrieve it, this will strengthen the connection to it. Long term memory holds primarily semantic memories (memory based on meaning).

b) Capacity - 

STM (short term memory) - 7 plus or minus 2 items can be stored in short term memory at one time.

LTM (long term memory) - Capacity for long term memory, as well as duration, is thought to be infinite.