The Memory Pyramid

orangesvetElectronics - Devices

Nov 8, 2013 (4 years and 5 months ago)


The Memory Pyramid

We take a look at how memory is organized

We also compare ROM and RAM

We look at hard disk access speed

CD and DVD are introduced

Tapes are discussed

In the end, the memory pyramid is

Memory Structure











Memory Structure

Exactly one cell is to be selected out of

An address means “serial number” of the
cell to be read or written

Addressing a cell means selecting a specific
cell so that only this cell is altered

Address decoding logic is part of memory


RAM is random access memory

RAM is volatile, readable, write

ROM is read only memory

ROM is permanent and only readable

Flash Memory is a PROM (programmable
ROM). It is write
able but it saves the data
even when power is turned off. It is used in
digital cameras.

Hard Disk Structure

Hard Disk Cylinders

Memory vs. Hard Disk

Memory access time is in the range of 60ns

Hard disk access time is in the range of 9ms

60ns means 60 X 10 (power
9) seconds

9ms means 9 X 10 (power
3) seconds

Comparing the powers tells us that hard
disk is much slower than the memory

Data Storage

We have compared hard disk with main
memory (RAM and ROM)

Disk is magnetic and RAM/ROM are

RAM also has two types. The fastest and
most expensive RAM is built with flip flops
and it is called static RAM (or SRAM)

The slow and dense RAM is built with capacitors
and it is called dynamic RAM or DRAM


SRAM is used as cache (L1 and L2) in

DRAM is used as main memory in the

There is only a little amount of SRAM and
a large amount of DRAM in a computer

Compaq Presario $849.99

Computer Specifications

800MHz AMD® Duron™ Processor

200MHz System Bus

128KB L1 Pipeline Burst Cache

64KB L2 Pipeline Burst Cache

64MB 100MHz SyncDRAM, three total DIMM slots
upgradable to 768MB (SyncDRAM DIMM required)

40.0GB UltraDMA hard drive

48X Max CD
ROM drive

RW Drive

NVidia™ TNT2™ Vanta LT Graphics Card with 8 MB
video memory

Maximum non
interlaced resolution of up to 1600 x
1200 @ 75 Hz (when supported by monitor)

Compact Disk

Compact Disk or CD is optical storage

The Spiral

CD’s have a single spiral of data starting
from the center and spiraling around until it
reaches the outer surface

If straightened, the total length of the data
spiral would be 5.6km (CD has a dia of 5”)

The CD’s use optical properties to record
0’s and 1’s

The Spiral

Pits and Lands

Information on a CD is recorded by using a
high power laser to burn 0.8 micron holes
(pits) in the surface

Since pit/land transition is taken as 1, the
binary data can be easily recorded

When playing a CD, a lower power laser
shines over the track

Pits and lands reflect different amounts of light
thus sensing 1’s and 0’s is straightforward

Capacity and Speed

CD stores 650MB of information

What is the X in CD speed? (e.g. 32X, 48X)

‘X’ reads as “times”

The single speed CD drive runs at 153,600
bytes per second

A 48X drive would run at 48*153,600 =
7,372,800 bytes per second (7.03MB/s)

New Kid on the Block!!

DVD is the new kid on the block in the CD

DVD is Digital Versatile Disk. It has same
working principles as a CD

It has smaller pits, tighter spiral and
different type of laser so its capacity is
minimum 4.7GB and maximum 17GB

1X DVD drive would run at 1.4MB/s


Magnetic tapes mounted in spools remind
us of the early mainframe computer era

Tapes have not become obsolete though

System managers still like to backup the
data on tapes (14GB capacity is huge!!)

Tapes have sequential access. You cannot
jump to the middle (remember FF and

The Memory Pyramid