lecture5

Memory Organization

5.1 The Memory Hierarchy
One of the most important considerations in understanding the performance capabilities of a modern processor are the memory hierarchy. not all memory is created equal, and some types are far less efficient and thus cheaper than others. To deal with this disparity, today s computer systems use a combination of memory types to provide the best performance at the best cost. This approach is called hierarchical memory. As a rule, the faster memory is, the more expensive it is
per bit of storage. By using a hierarchy of memories, each with different access speeds and storage capacities, a computer system can exhibit performance above what would be possible without a combination of the various types.
The memory hierarchy can be characterized by a number of parameters.
Among these parameters are the (access type, capacity, cycle time, latency, bandwidth, and cost).
. The term access refers to the action that physically takes place during a read or writes operation.
. The capacity of a memory level is usually measured in bytes.
. The cycle time is defined as the time elapsed from the start of a read operation to the start of a subsequent read.
. The latency is defined as the time interval between the request for information and the access to the first bit of that information.




The bandwidth provides a measure of the number of bits per second that can be accessed.
. The cost of a memory level is usually specified as costs per megabytes