The Memory Pyramid

orangesvetElectronics - Devices

Nov 8, 2013 (3 years and 9 months ago)

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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
constructed

Memory Structure

Cells

Containing

Data

A

d

d

r

e

s

s

Memory Structure


Exactly one cell is to be selected out of
millions


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 vs. ROM


RAM is random access memory


RAM is volatile, readable, write
-
able


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
electronic


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 vs. DRAM


SRAM is used as cache (L1 and L2) in
computers


DRAM is used as main memory in the
computers


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


CD
-
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
device


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
-
world


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

Tapes


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
REW?)

The Memory Pyramid