Question

Considering the datasheet of a recent model memory (RAM), very briefly identify its corresponding structure and function characteristics, specifically considering that it would be necessary to design a storage system that scales several times its base storage capacity (total number of locations and word width of the chip). Explain the advantages and disadvantages of making an interleaved memory bank compared to using a chip of the desired size.

Answer 1

Whenever, Processor request Data from the main memory. A block (chunk) of Data is Transferred to the cache and then to Processor. So whenever a cache miss occurs the Data is to be fetched from main memory. But main memory is relatively slower than the cache. So to improve the access time of the main memory interleaving is used.

Advantages :
Allocating memory is easy and cheap
Any free page is ok, OS can take first one out of list it keeps
Eliminates external fragmentation
Data (page frames) can be scattered all over PM
Pages are mapped appropriately anyway
Allows demand paging and prepaging
More efficient swapping
No need for considerations about fragmentation
Just swap out page least likely to be used


Disadvantages :
Longer memory access times (page table lookup)
Can be improved using TLB
Guarded page tables
Inverted page tables
Memory requirements (one entry per VM page)
Improve using Multilevel page tables and variable page sizes (super-pages)
Guarded page tables
Page Table Length Register (PTLR) to limit virtual memory size
Internal fragmentation