DDR2 User Controlled Refresh

i) SDRAM requires a refresh every 64ms. This is done a row at a time, usually there are 8192 rows so if you space these out evenly you need to do a refresh every 7.8us. However, JEDEC spec for SDRAM allows you to do up to 9 row refreshes back to back, thus allowing a longer period before doing another batch, which may help with efficiency in some systems

ii) minutes is not that unusual under ideal conditions, tens of minutes would be.

iii) refresh is done on a per row basis

iv) only a row is refreshed, so i think what they mean by burst is doing up to 9 as mentioned above