The classful network A provides 16,777,216, the most available in classful networks.
Unfortunately a class A network only allows for 256 possible networks.
This is of course IPv4 stuff
Remember the entire IPv4 address space is 32 bits wide
In class A the network mask is 255.0.0.0 meaning that the first octet or eight spaces are reserved for networks and the remaining 24 bits are available for host.
OK so the number of host are 2^24 or 16,777,216 English 16 million 777 thousand and 216 hosts
And don't forget all networks and subnets require reserving the first and last address for the network and the broadcast address.
Class A - it has 16,777,214 maximum clients per network.
class C
This question is unanswered.
in Class A addresses the first bit identifies the class. The next 7 bits identify the network and the rest are the IP's that belong to that network. However these networks are then broken down using subnets . Class A networks are not given to private clients or small private organisations. So if you want to know how many bits are there for identifying hosts in a Class A network, the answer is 32-8 = 24 bits. However if you mean how many bits are reserved for hosts in your private network space, that depends on your subnet and router. Most routers use NAT to allow multiple hosts to use a single external IP address. I hope this answers your question :)
Class 2
A class ip address offer the most number of host
A class A would give you the most flexibility in terms of subnets and hosts per subnet. You could use up to 23 bits of information for subnets.
Class B
Middle class
Class A, B and C Based on the split of the 32 bits, an IP address is either Class A, B or C, the most common of which is Class C. More than two million Class C addresses are assigned, quite often in large blocks to network access providers for use by their customers. The fewest are Class A networks, which are reserved for government agencies and huge companies. Although people identify the class by the first number in the IP address (see table below), a computer identifies class by the first three bits of the IP address (A=0; B=10; C=110). This class system has also been greatly expanded, eliminating the huge disparity in the number of hosts that each class can accommodate (see http://www.answers.com/topic/cider). See http://www.answers.com/topic/private-ip-address-technology and http://www.answers.com/topic/ip-technology. NETWORKS VERSUS HOSTS IN IPV4 IP ADDRESSES Maximum Maximum Number ofClass Number Hosts Bits used in Number of per Network/Host Class Range Networks Network ID ID A 1-126 127 16,777,214 7/24 B 128-191 16,383 65,534 14/16 C 192-223 2,097,151 254 21/8 127 reserved for loopback test Networks, Subnets and Hosts An IP address is first divided between networks and hosts. The host bits are further divided between subnets and hosts. See subnet mask.
A class C address.
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Just a little caveat here, what Archangel dmitry lists here is true but should be regarded as only historical information since classed IP address assignment has not been used in over 20 years. It was replaced in 1993 by Classless Inter-Domain Routing. This was put in place to help deal with the quick depletion of available public IP addresses. In the modern day, IP addresses are assigned as needed rather than as blocks as was done when classed addressing was used.
A class C network supports the most networks - the first three octets or 24 bits gives the largest grouping of networks.