1.4 Computer memory 13
1.3.2.Subtract the binary of 7 from the binary of 10, and confirm that the
result is the binary of 3.
1.3.3.Multiply the binary of 7 with the binary of 3, and confirm that the result
is the binary of 21.
1.3.4.Find the inverse of the number 5.0 by carrying out multiplications alone,
using the method discussed in the text.
1.4 Computermemoryandaddresses..................
The central processor receives information from, and deposits information to, a
memory unit housed in an external memory bank mounted on the motherboard.
The individual slots are identified bymemory addresses. It is important to make
a distinction between a memoryaddressand a memorycontentat the outset.
In contemporarybyte-addressable architectures, each address is associated
with a memory slot consisting of one byte. Long data are stored in multiple
bytes identified by a number of consecutive addresses. The real number 9.34556
absorbs more addresses than the integer 124.
Computer architectures are designed to work with memory addresses
whose maximum possible value is expressed by the number of bits allocated
to the memory addressing system:
- A 24-bit memory addressing system can accommodate 2^24 = 1,6777,216
addresses, and this limits the maximum number of memory slots to sixteen
Mbytes. - A 32-bit memory addressing system can accommodate 2^32 = 4,294,967,296
addresses, and this limits the maximum number of memory slots to four
Gbytes. At the present time, computers with that much memory are rare. - A 64-bit memory addressing system can accommodate 2^64 =1. 8446744
07370955 × 1019 addresses, and this limits the maximum number of mem-
ory slots to sixteen Ebytes.
In a 32-bit memory addressing system, the first memory address is 0 and the
last memory address is 4,294,967,296.
RAM
The random access memory (RAM) is the primary memory bank. Its
name reflects the ability to access the individual memory addresses at about
the same amount of time, independent of the memory location last visited. In
contrast, information stored in an external storage device, such as a hard drive
or a CD-ROM, is accessed sequentially.