About IAS:
IAS: immediate access storage.
Read more at https://ictsmart.tripod.com/ict4/online/artstrr.htm
These two webpages make me believe that IAS is just another name of Primary storage.
The main memory is a kind of primary storage.
The Cache memory is a kind of primary storage.
0478_S18_ms_11 shows IAS holds data and instructions when they are l