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
A
d
d
Cells
r Containing
e
Data
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