Types of internal memory

2.  RAM
 Misnamed as all semiconductor memory is random
access
 Read/Write
 Volatile (contents are lost when power switched off)
 Temporary storage
 Ram is of two types i.e., Static or dynamic
 Dynamic is based on capacitors
 Static is based on flip-flops – no leaks, does not need
refresh

4.  Dynamic random-access memory (DRAM) is a
type of random-access memory that stores
each bit of data in a separate capacitor within
an integrated circuit. The capacitor can be
either charged or discharged; these two states
are taken to represent the two values of a bit,
conventionally called 0 and 1

5.  Stores data as charge on capacitors
 Charges leak
 Need refreshing even when powered
 Simpler construction
 Smaller per bit
 Less expensive
 Need refresh circuits
 Slower
 Used in main memory

6. Static random-access memory (SRAM or static
RAM) is a type of semiconductor memory that
uses bistable latching circuitry to store each bit.
The term static differentiates it
from dynamic RAM (DRAM) which must be
periodically refreshed.

7.  Bits stored as on/off switches
 No charges to leak
 No refreshing needed when powered
 More complex construction
 Larger per bit
 More expensive
 Does not need refresh circuits
 Faster
 Cache
 Digital
 Uses flip-flops

9.  Both volatile
 DRAM is simpler and smaller than SRAM
 DRAM is less expensive than SRAM
 DRAM is favored for large memory
requirements
 SRAM are faster than DRAM
 SRAM is used for cache memory and DRAM is
used for main memory

10.  Programmable ROM
 Erasable Programmable ROM
 Electrically Erasable Programmable ROM
 Flash Memory

11.  A memory chip on which data can be written
only once.
 The difference between a PROM and
a ROM (read-only memory) is that a PROM is
manufactured as blank memory, whereas a
ROM is programmed during the
manufacturing process

12.  Erasable programmable read only memory, is
a type of memory chip that retains its data
when its power supply is switched off.
 Once programmed, an EPROM can be erased
by exposing it to strong ultraviolet light source

13.  It is a type of non-volatile memory used in
computers and other electronic devices to store
small amounts of data that must be saved
when power is removed.
 EEPROMs can be programmed and erased in-
circuit, by applying special programming
signals.
 the number of times it could be reprogrammed
is limited.

14.  Flash memory is an electronic non-
volatile computer storage medium that can be
electrically erased and reprogrammed.
 Flash memory is a specific type of EEPROM
where large amounts of static data are stored
(such as in USB flash drives)

15. 256-KB Memory Organization
• Multiple
chips make
up the entire
memory.
• 1 bit per chip
system org.
• 8 256K x 1
bit chips.

16. Module Organisation (2)
1-MB Memory Organization

17. • Hard Failure
o Permanent defect
• Soft Error
o Random, non-destructive
o No permanent damage to memory
o Present in all materials
• Detected using Hamming code
• Can be also repaired using error correcting
code
• SEC-DED code: single error correcting -
double error detecting code
o can detect 2 errors, can correct 1

20. In an interleaved memory, the memory
is divided into a set of banks. One way
of allocating virtual addresses to
memory modules is to divide the
memory space into contiguous blocks.
In an interleaved memory, however,
consecutive addresses reside in different
banks.

21. For example, suppose there are 4 banks, each containing
256 bytes. The interleaved scheme would assign
addresses 0, 4, 8, to the first bank, 1, 5, 9, to the second
bank, and so on.

22. However the memory space is split up
among the banks, as long as requests are
sent to two different banks they can be
handled simultaneously. The processor can
request a transfer from location i on one
cycle, and on the next cycle request
information from location j . If i and j are in
different banks, the information will be
returned on successive cycles.

23. In recent years ,a number of enhancements to the basic
DRAM architecture have been explored , and the schemes
that currently dominate the market are –
•SDRAM
•DDR – DRAM
•RDRAM

24. Synchronous dynamic random access
memory (SDRAM) is dynamic random access
memory (DRAM) that is synchronized with
the system bus. Classic DRAM has an asynchronous
interface, which means that it responds as quickly as
possible to changes in control inputs. SDRAM has a
synchronous interface, meaning that it waits for
a clock signal before responding to control inputs and
is therefore synchronized with the computer's system
bus. The clock is used to pipelines incoming
commands.
The data storage area is divided into several banks,
allowing the chip to work on several memory access
commands at a time. This allows higher data access
rates than an asynchronous DRAM.

25. Rambus Dynamic Random Access Memory (RDRAM) is a
memory subsystem designed to transfer data at faster rates.
RDAM is made up of a random access memory (RAM), a
RAM controller and a bus path that connect RAM to
microprocessors and other PC devices.
RDRAM was introduced in 1999 by Rambus, Inc. RDRAM
technology was considerably faster than older memory
models, like the Synchronous DRAM (SDRAM). Typical
SDRAM has a data transfer rate of up to 133 MHz, while
the RDRAM can transfer data at a speed of upto 800 MHz.
RDRAM is also known as Direct RDRAM or Rambus.

26. The enhanced version of SDRAM is DDR SDRAM (double data
rate SDRAM) that overcomes the once-per-cycle limitation. It can
send data to the processor twice per clock cycle.
DDR SDRAM (double data rate SDRAM) is synchronous
dynamic RAM (SDRAM) that can theoretically improve memory
clock speed to at least 200 MHz*. It activates output on both the
rising and falling edge of the system clock rather than on just the
rising edge, potentially doubling output.

27. Cache DRAM, integrates a small SRAM cache
(16Kb) onto a generic Dram chip.
The SRAM on the DRAM can also be used as
a buffer to support the serial access of a block
of data.