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Memory and Storage
Chapter 9
Memory
• Memory ( from programmer’s point of view): Temporary storage to
hold data as well as programs.
• An Architect views memory as a solid state digital device that
provide storage for data values.
When an architect designs memory two key choices:
- Technology
- Organization
Technology: properties of the underlying hardware mechanisms
used to construct the memory systems.
Organization: the way the underlying technology is used to form
a working system.
Characteristics Of Memory
Technologies
Memory technology is characterized by several issues:
- Volatile or nonvolatile:
- Random or Sequential :
- Primary or Secondary
- Read-Write or Read-only:
Read-Write: The values in the memory can be accessed or updated at
any time.
Read-only: The memory can be accessed but not changed .
Different forms of ROM are:
PROM: allows data values are burnt on the chip using high voltage , can
be entered only once.
EEPROM: values can be altered, but takes longer time than reading
them.
Flash ROM is a variant of EEPROM.
Concept of Memory Hierarchy
• Memory which has the highest performance characteristics is most
expensive.
• The set of technologies should be arranged in a conceptual memory
hierarchy.
• Architect selects the highest performance (costly)memory to be in
smallest size.
• Ex: an architect selects a small number of general purpose registers and
large amount of secondary memory.
• The levels of memory in a computer. From fastest to slowest speed, they
are:
1. CPU registers
2. L1 cache
3. L2 cache
4. Main memory
5. Virtual memory
6. Disk
Instruction And Data Store
The modern computer systems place program and data in a single
memory(Von Neumann Architecture). The instructions and data are
stored as separate stores to enhance performance.
• Instruction Store:
- Memory used to store program.
- Its needs higher performance, high speed instructions are designed
to operate on values in general purpose registers rather than in
memory.
- An instruction is fetched every clock cycle.
• Data Store:
-Memory used to store Data.
-This is less active than the Instruction store.
- Data values may also be a part of the instruction itself (immediate
reference)
Key Points
• Memory Technology & Organization
• Memory Hierarchy
• Instruction & Data Store