Unit 1
OMT
Memory

SRAM
• SRAM (static RAM) is a type of random access
memory (RAM) that retains data bits in its
memory as long as power is being supplied.
Unlike dynamic RAM (DRAM), which must be
continuously refreshed, SRAM does not have
this requirement, resulting in better
performance and lower power usage.
However, SRAM is also more expensive than
DRAM, and it requires a lot more space.

For example
• Time in market: 1990s to present
• Popular products using SRAM: Digital cameras, routers, printers,
LCD screens
It might be part of a RAM digital-to-analog converter (RAMDAC) on a
computer's video or graphic card. It might also be used in a disk
drive as buffer cache, in a peripheral such as a printer or LCD
display, or in a network device such as router or switch.
• SRAM can be found in other devices ways as well. For example,
SRAM chips are often used in cell phones, wearables and other
consumer electronics. They might also be embedded in medical
products, which can include anything from hearing aids to body
area networks that include multiple devices embedded in the body.
In addition, SRAM is used in toys, appliances, automobiles,
industrial equipment and a wide range of IoT devices.

States of SRAM :
• It can be in 3 states, namely –
• Standby – It is a condition in SRAM when SRAM’s
circuitry is sitting idle and no work is given to a
particular SRAM. It can underutilize the capacity of the
resources available.
• Reading – It is a condition in SRAM when the data has
been requested to be fetched. It puts the SRAM’s
circuitry in working condition.
• Writing – It is a c condition in SRAM when the data has
to be updated or overwritten stored in Async SRAM.
This state will also put SRAM’s circuitry in working
condition.

Types of SRAM
• Non-volatile SRAM
• (nvSRAM) has standard SRAM functionality,
but they save the data when the power supply
is lost, ensuring preservation of critical
information. nvSRAMs are used in a wide
range of situations – networking, aerospace,
and medical, among many others – where the
preservation of data is critical and where
batteries are impractical.

2.Asynchrous SRAM
• First of all, let us see what is meant by
asynchronous here. The devices that do not
depend on external clock pulse for their
working, these devices are called
asynchronous devices, and the SRAM which
does not depend on an external clock for its
working is known as asynchronous SRAM.

By feature
• (Zero bus turnaround) (ZBT) – the turnaround is the
number of clock cycles it takes to change access to the
SRAM from write to read and vice versa. The
turnaround for ZBT SRAMs or the latency between read
and write cycle is zero.
• Sync Bust (syncBurst SRAM or synchronous-burst
SRAM) – features synchronous burst write access to
the SRAM to increase write operation to the SRAM.
• DDR SRAM – synchronous, single read/write port,
double data rate I/O.
• Quad Data Rate SRAM – synchronous, separate read
and write ports, quadruple data rate I/O.

Dynamic RAM(DRAM)
• DRAM, or dynamic random access memory, implies,
this form of memory technology is a type of random
access memory. It stores each bit of data on a small
capacitor within the memory cell. The capacitor can be
either charged or discharged and this provides the two
states, "1" or "0" for the cell.
• Since the charge within the capacitor leaks, it is
necessary to refresh each memory cell periodically.
This refresh requirement gives rise to the term
dynamic - static memories do not have a need to be
refreshed.

• The advantage of a DRAM is the simplicity of the
cell - it only requires a single transistor compared
to around six in a typical static RAM, SRAM
memory cell. In view of its simplicity, the costs of
DRAM are much lower than those for SRAM, and
they are able to provide much higher levels of
memory density. However the DRAM has
disadvantages as well, and as a result, most
computers use both DRAM technology and
SRAM, but in different areas.

SDRAM
• Synchronous Dynamic Random Access
Memory (SDRAM)- ‘Synchronous’ relates to
the behavior of the Dynamic Random Access
Memory type that synchronizes with the clock
system of the computer, thus making it easier
to manage it quicker.

• SDRAM has undergone changes and the recently
updated version delivers better performance.
Given below are some generations of SDRAM:
– DDR SDRAM( double data rate (DDR) synchronous
dynamic random-access memory (SDRAM))
– DDR2 SDRAM
– DDR3 SDRAM
– DDR4 SDRAM
– DDR5 SDRAM