1. Module one / unit 4
Memory
By Kenneth Ayebazibwe
256774185458 / 256702555890
kynaye@gmail.com

2. Objectives
• On completion of this unit, you will be able to;
– Distinguish RAM and ROM memory techniques
– Describe the memory types SDRAM, RDRAM, DDR/
DDR2 and SRAM and give examples of how they are
used
– Identify DIMM and RIMM memory packaging for
different technologies
– Understand the characteristics of different memory types
– Double sided
– ECC
– registered

3. Memory Types
• RAM - Random Access Memory
ROM - Read-Only Memory
– RAM is the piece of memory where the programs and files you are
using are stored, thus the files found in your RAM changes all the
time (e.g MSN, Firefox, Word Docs, etc remains in RAM if you are
using it). When your PC is switched off, data in your RAM is gone
and cannot be recovered unless it has been saved on a permanent
memory that is Hard Disk.
ROM is the place where data that you cannot alter is stored, for
example BIOS or Bootstrap Loader. ROM is used in the computer
so that the processor does not have to look for important pieces of
data when switched on, The processor just finds it in the ROM.
You cannot edit files in ROM and data on it cannot be erased by
turning off your PC

4. Types of RAM: How to Identify and their
Specifications
• There are many different types of RAM which
have appeared over the years and it is often
difficult knowing the difference between them
both performance wise and visually identifying
them.

5. FPM RAM
• FPM RAM, which stands for “Fast Page
Mode RAMâ€Â
(DRAM). The term “Fast Page ModeÃ
¢â‚¬Â) comes from the capability of memory
being able to access data that is on the same page
and can be done with less latency. Most 486 and
Pentium based systems from 1995 and earlier use
FPM Memory.
•

6. EDO RAM
• EDO RAM, which stands for “Extended Data
Out RAMâ€Â
available for Pentium based systems. EDO is a modified form of
FPM RAM which is commonly referred to as “Hyper
Page Modeâ€Âs . Extended Data Out refers to fact that the
data output drivers on the memory module are not switched off
when the memory controller removes the column address to
begin the next cycle, unlike FPM RAM. Most early Penitum
based systems use EDO.

7. SDRAM
• SDRAM , which is short for Synchronous DRAM is a type of
DRAM that runs in synchronization with the memory bus.
Beginning in 1996 most Intel based chipsets began to support
SDRAM which made it a popular choice for new systems in
2001.
SDRAM is capable of running at 133MHz which is about three
times faster than FPM RAM and twice as fast as EDO RAM.
Most Pentium or Celeron systems purchased in 1999 have
SDRAM.

8. DDR RAM
• DDR RAM, which stands for “Double Data RateÃ
¢â‚¬ÂA which is a type of SDRAM and appeared first on the
market around 2001 but didn’t catch on until about 2001 when
the mainstream motherboards started supporting it. The
difference between SDRAM and DDR RAM is that instead of
doubling the clock rate it transfers data twice per clock cycle
which effectively doubles the data rate. DDRRAM has become
mainstream in the graphics card market and has become the
memory standard.

9. Memory Packaging
• Memory is available in various physical packaging. Roughly in order of
their appearance, the major types of DRAM packaging include:
– DIP (Dual Inline Pin Package)This package comprises a rectangular chip
with a row of pins down each long side, making it resemble an insect.
DIP was the most common DRAM package used in PCs through early
386 models. DIP chips were produced in Page Mode and Fast Page
Mode, and are long obsolete. DIP packaging was also used for L2 cache
memory on most 486 and some Pentium-class motherboards. DIP
DRAM is useless nowadays.
– SIPP (Single Inline Pin Package)This package turns a DIP chip on its side
and extends all leads straight out one side, parallel to the plane of the
chip. SIPPs were intended to allow memory to be installed more densely,
and were used in a few 386SX systems, but they never caught on. SIPPs
were produced in Page Mode and Fast Page Mode form, and are long
obsolete.

10. – SIMM (Single Inline Memory Module)This package mounts multiple
individual DRAM DIP chips on a small circuit board with a card-
edge connector designed to fit a socket on the motherboard.
Mainstream SIMMs have been manufactured in two form factors:
• 30-pinThese SIMMs were used in a few 286 systems, most 386 systems,
and some 486 systems, and were produced in Page Mode and Fast Page
Mode form. Although they are still available, 30-pin SIMMs are obsolete.
If you tear down an old system, any 30-pin SIMMs you salvage are too
small and too slow to be useful. However, some laser printers do use
them.
• 72-pinThese SIMMs were used in some 386 systems, most 486 systems,
and nearly all Pentium-class systems built before the advent of DIMMs.
72-pin SIMMs were produced in Fast Page Mode, EDO form, and
BEDO form. When tearing down old systems, 72-pin SIMMs may be
worth salvaging, as they can be used to expand the memory on a late-
model Pentium or Pentium Pro system or to expand the memory in some
laser printers.

11. • Figure shows a 72-pin SIMM (top) and a 30-pin
SIMM. The 72-pin SIMM is keyed by the notch
at the bottom right; the 30-pin SIMM by the
notch at the bottom left. The holes on either
side immediately above the bottom row of
contacts are used by the slot retention
mechanism to secure the SIMM in the slot.
Although it may not be visible in the
reproduction, the top SIMM uses gold contacts
and the bottom SIMM tin contacts.

12. 72-pin SIMM (top) and 30-pin SIMM

13. • DIMM (Dual Inline Memory Module)DIMMs are dual-side modules that use
connectors on both sides of the circuit board. SDR-SDRAM DIMMs have
168 pins, but SDR-SDRAM is also available in 100- and 144-pin DIMMs.
DDR-SDRAM is packaged in 184-pin DIMMs, which are physically similar to
standard 168-pin SDR-SDRAM DIMMs, but have additional pins and
different keying notch positions to prevent them from being interchanged.
DDR-II DIMMs are similar to DDR DIMMs, but use a 232-pin connector.
Only SDR-SDRAM, DDR-SDRAM, and EDO are commonly packaged as
DIMMs.
• SODIMM (Small Outline DIMM)A special package used in notebook
computers and on some video adapters.
• RIMMA Rambus RDRAM module. RIMM is a trade name rather than an
acronym. RIMMs are physically similar to standard SDRAM DIMMs, except
that the keying notches are in different locations. RDRAM is available in 168-
pin and 184-pin modules. Early RDRAM motherboards used 168-pin
RIMMs. Most current RDRAM motherboards use 184-pin RIMMs.

14. • Figure shows the two most common physical packages for
memory used in recent systems. The top module is a 168-pin
PC133 SDRAM DIMM. The bottom module is a 184-pin
PC2100 DDR-SDRAM DIMM (faster DDR-SDRAM
modules use the same package). The physical dimensions of
both are the same: 5.375 inches (13.6525 cm) wide by 1.375
inches (3.4925 cm) tall. The width is standardized for all
memory modules to ensure they fit the standard slot. The
height may vary slightly, and is a factor only in that tall
modules may interfere with other components in a tightly
packed system. Both of these modules use nine chips, which
indicates that they are Error Checking and Correction (ECC)
modules. Nonparity modules use only eight chips.

15. PC133 SDRAM DIMM (top) and PC2100
DDR-SDRAM DIMM

16. • The major difference between these DIMMs, other than
the number of pins, is the location of the keying notches.
SDRAM DIMMs use two notches, one centered and one
offset. DDR-SDRAM DIMMs use only one offset keying
notch. The number and position of these keying notches
ensure that only the proper memory type can be installed
in a slot and that the module is oriented correctly.
Rambus RIMMs use similar physical packaging, but with
the keying notches in different locations. Rambus RIMMs
also cover the individual chips with a metal shroud
designed to dissipate heat.

17. Characteristics of Memory
• Memory, also known as RAM (Random Access
Memory), provides a place for your PC to store
information before writing / reading it to the hard
drive. Its other use is to allow programs to run
simultaneously without slowing your PC speed.
Memory is also one of the cheapest ways to
upgrade your computer's speed so if you ever need
to find out what memory setup you have or how
good another setup is, you should know the key
memory characteristics and what they mean.

18. • DDR
– DDR, DDR2 and DDR3 stand for Double Data Rate. They are the measurement at which your
memory transfers data chunks in a clock cycle. All memories work in clock cycles to synchronize
their processes and a DDR unit transfers 2 data chunks per cycle. This means that a DDR memory
will transfer twice as much data as an old memory unit would running the same length of clock
cycle. Old memory units were SDRAM memories, which are not available for PCs anymore. The
differences between DDR, DDR2 and DDR3 are their respective generations; the 3rd generation
of DDR memory has a higher rate value than a DDR 1st generation.
• Memory Clock Speed
– The memory clock speed of computer memory is written in MHz. This is the value that
determines how quickly the computer can transfer the memory on your PC. The total value that
your memory can achieve is usually written after the DDR, DDR2 or DDR3 value. For example,
DDR2-667 would represent 667 MHz. However, it is important to understand that the standard
clock speed of the memory is always half of what is advertised; in this case, 333 MHz. This is
because the DDR always runs at double the speed of what an old memory unit would have.
Writing a DDR MHz value is the standard advertising values for memory chips.

19. • Memory Megabytes
– Memory is measured in Megabytes, written as Mb.
Standard practice for advertising memory units is to
present it as a PC number with the Mb value written
afterwards; for example PC6400. The MB value (6400)
represents how much data is transferred per second and
the higher the Mb value the more data that can be
transferred. The Mb value is usually calculated by using
the memory's clock frequency (MHz) and multiplying it
by 8. This, however, is not always the exact number
because manufacturers avoid selling memory with
complicated numbers (e.g. 1066 MHZ x 8 = P8528) and
instead round it up or down, in this case PC8500.