Java Reference
In-Depth Information
buildingblocksofcomputersystems.Inmostmoderncomputers,memory
cells,registers,anddatapathsaredesignedinmultiplesoffourbinarydig-
canbeencodedinasinglehexdigit.
Computer memory
Todaycomputermemoryisusuallyfurnishedintheformofasilicon
waferthathousesapackageofintegratedcircuits.Eachmemorycellisa
transistorcircuitcapableofstoringtwostablestates.Onestateisrepre-
sentedwiththebinarysymbol1andtheotheronewiththebinarysymbol
0.Thememorycellsareusuallyarrangedingroupsof8bits,calleda
byte
.
Inmostmachines,thebyteisthesmallestunitofmemorythatcanbedi-
rectlyaccessedbyaprogram.
Table3-1
liststhemostcommonunitsofmeasurementassociatedwith
computermemory.
Table3-1
Units of Memory Storage
UNIT
EQUAL TO
nibble
4 bits
byte
8 bits
2 nibbles
word
16 bits
4 nibbles
2bytes
kilobyte
1024 bytes
megabyte
1024 kilobytes
gigabyte
1024 megabytes
Memory is organized linearly, that is, memory cells are placed in a sin-
gle straight line that extends from the first to the last cell in the system.
The sequential number assigned to each unit is called the
memory ad-
dress
. The maximum number of memory units in a particular system de-
pends on its internal architecture. Each memory cell in a typical com-
puterconsistsofonebyte(8bits)ofdata.
Figure3-2
showsthe
numbering of the individual bits within a byte.
Character data
Computers store data in groups of electrical cells, each of which holds ei-
ther binary 1 or 0. These patterns of 1's and 0's are the most efficient and
convenient way of representing computer information. A group of eight
cells, called a byte, stores a number in the range 0 to 255.
