What does 64K means In a SIM Card?

Many of us don’t know the meaning of 64k written on the SIM card. In many forum it is said the the 64K is refer to the total memory available in the SIM card. I don’t know whether it is correct or not. Recently I was studying the digital communication subject. In this subject there is a chapter of Pulse Code Modulation (PCM) and Digital Multiplexers. In this chapter, I found a topic on TI carrier system(PCM-TDM System). It says that according to North-American hierarchy of telephony system-both for analog and digital system- a PCM voice signal represents 64k bits/sec i.e., 8000 samples per sec x 8 bits per sec.. also that due to 8000 samples per sec, the sampling rate, the time duration between adjacent samples will be (1/8000) or 125 micro seconds.
Now you can see that in actual telephony system, 64K stands for the data transfer rate and of course the speed of data (digital signal) transfer. higher the rate, higher speed of data accessing and transferring. Some years back, when the mobile phones came into market, you might have noticed that 32K was written on the place of 64K of now-a-days SIM card. that means the data transfer rate was very low then and we could not surf/browse internet thru’ our mobile phones. Today, 64K, 128K SIM Cards are available. We all know that 64K is 2G and 128K SIMs are 3G.
So , according to my limited knowledge, 64K should stands for the data transfer rate or to be more precious, the sampling rate of that particular SIM card. I’m posting details of T1 carrier system here. To know more please go thru’ the next part.
T1-carrier System
The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission. The original transmission rate (1.544 Mbps) in the T1 line is in common use today in Internet service provider (ISP) connections to the Internet. Another level, the T3 line, providing 44.736 Mbps, is also commonly used by Internet service providers.

The T-carrier system is entirely digital, using pulse code modulation (PCM) and time-division multiplexing (TDM). The system uses four wires and provides duplex capability (two wires for receiving and two for sending at the same time). The T1 digital stream consists of 24 64-Kbps channels that are multiplexed. (The standardized 64 Kbps channel is based on the bandwidth required for a voice conversation.) The four wires were originally a pair of twisted pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media. A number of variations on the number and use of channels are possible.
A T1 line in which each channel serves a different application is known as integrated T1 or channelized T1. Another commonly installed service is a fractional T1, which is the rental of some portion of the 24 channels in a T1 line, with the other channels going unused.

In the T1 system, voice or other analog signals are sampled 8,000 times a second and each sample is digitized into an 8-bit word. With 24 channels being digitized at the same time, a 192-bit frame (24 channels each with an 8-bit word) is thus being transmitted 8,000 times a second. Each frame is separated from the next by a single bit, making a 193-bit block. The 192 bit frame multiplied by 8,000 and the additional 8,000 framing bits make up the T1's 1.544 Mbps data rate. The signaling bits are the least significant bits in each frame.