Memory interleaving splits memory into independent banks that can process read/write requests in parallel to increase throughput. It interleaves the address space so consecutive addresses are assigned to different banks. Low order interleaving uses the low order bits of an address to identify the memory module and high order bits for the word address within each module, allowing block access in a pipelined fashion. This improves the effective memory bandwidth.

1. 024

2. Memory Interleaving

Memory interleaving is the technique
used to increase the throughput. The
core idea is to split the memory system
into independent banks, which can
answer read or write requests
independents in parallel.

3. 4 Way interleaved
Memory
Low order interleaving

4. 
Usually , this is done by interleaving the
address space, Consecutive cells in the
address space are assigned to different
memory banks. An example of four-way
interleaved memory , and the mapping of
consecutive data cells it is shown in previous
slide.

5. There are two-address format for memory interleaving the
address space.
Low order interleaving
Low order interleaving spreads contiguous memory
location across the modules horizontally. This implies
that the low order bits of the memory address are used
to indentify the memory module. High order bits are the
word addresses (displacement) within each module
High order interleaving
High order interleaving uses the high order bits as the
module address and the low order bits as the word
address within each module.

6. Where is it implemented

Memory interleaving implemented on
main memory , Which is slow as
compared to Cache. And Main memory
having less bandwidth.

7. Memory bandwidth

Memory bandwidth is the rate at which
data can be read and write into
a memory by a processor. Memory
bandwidth is usually expressed in units
of bytes/sec.

8. Interleaved Memory
organization



Various organization of the physical memory
are included in this section. In order to close
up the speed gap between Cache and main
memory. And interleaving technique is
represented allow pipelined access of the
parallel memory modules.
The memory design goal (interleaving goal) is
to broaden the effective memory bandwidth so
that more memory words can be accessed per
unit time.
The ultimate purpose is to match the memory
bandwidth with the bus bandwidth and with the
processor bandwidth.

9. Modules and addresses in
Main Memory







The main memory is built with multiple modules
(chips).
These memory modules are connected to a bus and
other resources(Processor, I/O) are also connected.
Memory module having memory addresses.
Each memory module return one word per cycle.
It is possible to present different addresses to
different memory modules.
So the Parallel access of multiple word can be done
concurrently (one cycle).
This called parallel access in term of pipelined
fashion.

10. Main memory is often block-accessed at
consecutive addresses.
 Block access is needed for fetching a
sequence of instructions or for accessing a
linearly ordered data structure.
 Each block access may correspond to the
size of a cache block.
 Therefore it is desirable to design the
memory to facilitate the block access of
contiguous words.


11. The Address Space for Low–
Order Interleaving







When a memory is N–way interleaved, we always find
that N = 2K.
This is due to the structure of the memory address.
For K = 1, we have 2–way interleaving.
For K = 2, we have 4–way interleaving.
For K = 3, we have 8–way interleaving.
For K = 4, we have 16–way interleaving.
For each scheme, the K bits(lower bits) of the address
select the Module.
structure is as follows. Each address is a 6–bit
unsigned binary number.

12. A Main memory formed with m= 2^a memory
modules.
 Each containing w=2^b words of memory
cells.

a and b bits in Low order interleaving
a bits are used to identify the memory module. And the higher
order b bits are the word addresses(displacement) within each
module.
a and b bits in High order interleaving
a bits are as the module address and the low order b bits are the
word address in each module.
High order interleaving cannot support block access of
contiguous location .
Low order interleaving support the block access in pipelined
fashion .

13. Low order interleaving

14. High order interleaving