MGMT 1050 Lecture Notes - Lecture 14: Conventional Memory, Flash Memory, Hard Disk Drive Performance Characteristics
MGMT 1050 Lecture 14 Notes – Conventional Memory
Introduction
• The data throughput rate of memory is determined primarily by the capability of the bus
and interfaces that connect memory to the CPU.
• Rates well in excess of 1 GB/sec are common in modern computers.
• Below the level of conventional memory, storage in the hierarchy is not immediately
available to the CPU, is referred to as secondary storage, and is treated as I/O.
• Data and programs in secondary storage must be copied to primary memory for CPU
access.
• Except for flash memory, access to secondary storage is significantly slower than
primary storage.
• Disks and other secondary storage devices are mechanical in nature, and mechanical
devices are of necessity slower than devices that are purely electronic.
• The location of the desired data is usually not immediately accessible, and the medium
must be physically moved to provide access to the correct location.
• This requires a seek time, the time needed to find the desired location.
• Once the correct data is located, it must be moved into primary memory for use.
• The throughput rate indicates the speed with which the transfer of data between
memory and the I/O device can take place.
• Most of the access time specified for secondary storage a device consists of seeks time.
• As a result of this access time, even the fastest disks are only about one-millionth as fast
as the slowest memory.
• It should be apparent that a lot of CPU instructions can be performed while waiting for a
disk transfer to take place.
• One important advantage of secondary storage, of course, is its permanence, or lack of
volatility.
• As noted RAM data is lost when the power is shut off.
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