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Memory Organization (Types of Memory (ROM (This memory can't be…
Memory Organization
Types of Memory
ROM
This memory can't be written, as its name says it can only be written. ROM memories can be written once, when they are manufactured. They are nonvolatile this means that even if the the electric supply stops the data inside it remains.
PROM
This is just like the ROM but it is not written when manufactures, instead they can be written once by a programmer or the person that is working with the memory. Used for CD disks.
EPROM
Works the same as the PROM but this type of memory can be erased. So the writing can be reversed to be written again.
RWM
This is a read write memory. Commonly known a RAM. It is volatile. Two types of RAM called SRAM and DRAM. SRAM retains the data value written in memory for as long the source of power remains. DRAM use tiny capacitors to store information, this capacitors need to be refreshed because they cant retain the charge for very long. It is a destructive memory type
Basic Memory Operations
Read
Reads a previously stored data. Needs memory address from where to read. It does not destroys the content when it reads it.
Write
Writes data to an specific location. Needs an address in memory and what to write in that address. It is destructive, when you write something in a memory location whatever was in that location is erased.
Two metrics characterize memory. Access time is the time required by the memory to retrieve the data from a memory location. Memory cycle time is the minimum time between successive memory operations.
Mapping Memory
Full Mapping
It is a one on one mapping function between the memory address and the MAS(Memory Address Space). This means that each space in the MAS has one and only one memory address. Useful in mapping a memory module.
Partial Mapping
This type of mapping reduced the complexity used in full mapping. Each memory location is mapped to more than one address in the MAS. It is more simplified if the amount of mappings to the MAS is a power of 2.
Storing Multibyte Data
Storing data often requires many many bytes. There are two types of byte ordering schemes. Little endian and big endian, they are very similar, and working with neither of them does not causes any trouble if the other computers you are working with use the same ordering scheme.
Building a Memory Block
Tri State Buffers
Normal devices in logic circuits have 2 states 1 or 0. Tri state buffers have a third state called Z state. In this state the outputs float making this type of buffer perfect for bus connections,
D Flip Flops
Each D Flip Flop hods a bit so a 2D Array of Flip Flops can be used to store a lot of words. So the amount of columns is the length of the word that can be stored and the amount of rows represents how many words can be stored. To form a memory block they are all tied together by the same clock signal. Each row has their own clock signal.