Memory

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Anjali G
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Geetha
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DIFFERENT TYPES OF MEMORIES IN A COMPUTER INCLUDING
REGISTERS

INTRODUCTION
 Computer memory is any physical device capable of storing information
temporarily or permanently.
two types: volatile and non volatile

VOLATILE MEMORY
Volatile memory is a temporary memory that loses its contents when the computer or
hardware device loses power.
Computer RAM is a good example of a volatile memory
 Most modern volatile memory is either Static RAM or dynamic RAM.
SRAM:-
 SRAM uses six transistors per bit.
SRAM is faster and more reliable than the more common DRAM . While DRAM supports
access times of about 60 nanoseconds, SRAM can give access times as low as 10
nanoseconds.
Unfortunately SRAM is much more expensive to produce than DRAM. Due to its high
cost, SRAM is often used only as a memory cache.
SRAM is generally used for high-speed registers & caches.

A typical SRAM cell is made up of six MOSFET.
Each bit in an SRAM is stored on four
transistors(M1, M2, M3, M4) that form
two cross-coupled inverters.
Main Needs:
• to provide a direct interface with the CPU at speeds
not attainable by DRAMs
• to replace DRAMs in systems that require very
low power consumption.
DRAM:-
DRAM is a type of random-access memory that stores
each bit of data in a separate capacitor within an IC.
The capacitor can be either charged or discharged; these two states are taken to
represent the two values of a bit.
Dynamic RAM needs regular refresh cycles to prevent its contents being lost.
The advantage of DRAM is its structural simplicity: only one transistor and a capacitor are
required per bit, compared to four or six transistors in SRAM.

DRAM is usually arranged in a rectangular array of charge storage cells consisting of one
capacitor and transistor per data bit.

VIRTUAL MEMORY
When computer lacks RAM; needed to run a program
or operation Virtual memory is used.
Virtual memory combines your computer’s RAM with
temporary space on your hard disk.
The purpose of virtual memory is to enlarge the
address space, the set of addresses a program can utilize.
The operating system divides virtual memory into pages,
each of which contains a fixed number of addresses. Each page is stored on a disk until it is
needed.
When RAM runs low, virtual memory moves data from RAM to a space called a paging
file. Moving data to and from the paging file frees up RAM to complete its work.
OS is translating virtual addresses into real addresses.
The process of translating virtual addresses into real addresses is called mapping. The
copying of virtual pages from disk to main memory is known as paging.

NONVOLATILE MEMORY
Non-volatile memory is computer memory that can retain the stored information even
when not powered.
 Examples of non-volatile memory include read-only memory , flash memory, most types
of magnetic computer storage devices (e.g. hard disks, floppy discs and magnetic tape)
Read-only memory (ROM) is a class of storage medium used in computers and other
electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly
or with difficulty, so it is mainly used to distribute firmware.
Flash memory is an electronic non-volatile computer storage device that can be
electrically erased and reprogrammed.
Flash memory was developed from EEPROM.
There are two main types of flash memory, which are named after
the NAND and NOR logic gates.

REGISTERS
A special, high-speed storage area within the CPU.
 All data must be represented in a register before it can be processed.
The number of registers that a CPU has and the size of each help determine the power
and speed of a CPU.
Only assembly language programs can manipulate registers.
Register performs:
1. Fetch: The Fetch Operation is used for taking the instructions those are given by the
user and the Instructions those are stored into the Main Memory will be fetch by using
Registers.
2. Decode: The Decode Operation is used for interpreting the Instructions means the
Instructions are decoded means the CPU will find out which Operation is to be
performed on the Instructions.
3. Execute: The Execute Operation is performed by the CPU. And Results those are
produced by the CPU are then Stored into the Memory and after that they are
displayed on the user Screen.

TYPES OF REGISTERS
Memory Address Register: -This register holds the memory addresses of data and
instructions. This register is used to access data and instructions from memory during the
execution phase of an instruction.
Program Counter:- The program counter (PC), commonly called the instruction pointer (IP)
in Intel x86 microprocessors. It keeps track of the the next memory address of the
instruction that is to be executed once the execution of the current instruction is
completed.
Accumulator Register:- Register is used for storing the Results those are produced by the
System.
Memory Data Register :- MDR is the register of a computer's control unit that contains
the data to be stored in the computer storage(e.g. RAM), or the data after a fetch from the
computer storage
Index Register:-A hardware element which holds a number that can be added to the
address portion of a computer instruction to form an effective address.
Data Register:-A register used in microcomputers to temporarily store data being
transmitted to or from a peripheral device.

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Memory

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