barcodefield.com

Memory in .NET Draw Data Matrix in .NET Memory




How to generate, print barcode using .NET, Java sdk library control with example project source code free download:
Memory generate, create none none in none projects Microsoft Office Excel Website Smart cards h none for none ave a memory architecture that will be unfamiliar if not downright bizarre to most mainstream programmers. Programmers typically think in terms of having available large amounts of homogeneous random access memory (RAM) that is freely available for reading and writing. This is definitely not the case on a smart card.

There are, in fact, three kinds of memory on a smart card: read-only memory (ROM), nonvolatile memory (NVM), and a relatively tiny amount of RAM. ROM is where the smart card operating system is stored and is of interest only to assembly language programmers. General-purpose smart cards have between 8 KB and 96 KB of ROM.

Here one finds various utility routines such as those for doing communication and for maintaining an on-card file system along with encryption routines and special-purpose arithmetic routines. Code and data are placed in readonly memory when the card is manufactured and cannot be changed; this information is hard-wired into the card. NVM is where the card"s variable data such as account numbers, number of loyalty points, or amount of e-cash is stored.

NVM can be read and written by application. programs, but it doesn"t act like and cannot be used like RAM. NVM gets its name from the fact that it happily retains its contents when power is removed from the card; data written to NVM, if not overwritten, will last 10 years. NVM presents two problems: Slowness.

It generally takes 3 to 10 milliseconds to write data into NVM. Data loss. NVM wears out after it has been written to a number of times (around 100,000 times).

. The typical p none none rogrammer is not familiar with either of these two problems, but must take them into account when writing smart card software. There is some familiar RAM on a smart card, but not very much usually only 2,000 bytes or less. This is unquestionably the most precious resource on the smart card from the card software developer"s point of view.

Even when using a high-level language on the smart card, the programmer is acutely aware of the need to economize on the use of temporary variables. Furthermore, the RAM is not only used by the programmer"s application, but also by all the utility routines, so a programmer has to be aware not only of how much RAM he or she is using, but also how much is needed by the routines he or she calls. A smart card CPU will not necessarily execute code from all parts of the smart card memory system.

Most smart card chips, for example, will not execute code stored in RAM. Furthermore, some chips make it possible to reconfigure sections of NVM so that a program loaded into NVM cannot be overwritten (essentially turning the NVM into ROM) or so that the CPU won"t take instructions and therefore execute code from this part of memory. These various types of memory used in smart card chips bring in a very interesting wrinkle with respect to the chip design for smart card ICCs.

The implementation technologies used for chip memories vary greatly in the size of individual memory cells as we saw illustrated in Figure 2.5. The smallest memory element is read-only memory.

This type of memory, as the name implies, can be read by typical computer elements, but it requires very special equipment in order to write information into the memory. In fact, the writing of ROM can be incorporated very early into the chip fabrication process itself; this technique tends to enhance the security of the chip because it is difficult to examine the contents of the ROM without destroying the chip, even with very expensive probing equipment. So this type of memory is very useful for permanently encoding stored programs for the smart card, but it is useless for storage of dynamic information that needs to be changed during the normal use of the card.

Significantly larger is the electrically erasable and programmable read-only memory (EEPROM). The contents of this type of memory in a smart card chip can actually be modified during normal use of the card. Hence, programs or data can be stored in EEPROM during normal operation of the card and then read back by applications that are using the card.

The electrical characteristics of EEPROM memory are such that it can only be erased and then reprogrammed a finite (but reasonably large) number of times, generally around 100,000 times. While somewhat limited, techniques have evolved which make this type of memory quite useful for typical smart card uses. EEPROM memory cells tend to be about a factor of four larger than ROM memory cells.

EEPROM, like ROM, does have the nice characteristic of being nonvolatile. memory; that is, the information content of the memory is unchanged when the power to the memory is turned off. So information content is preserved across power-up and power-down cycles on the smart card chip. Larger still is a memory type known as RAM.

This is the type of memory used in typical computer systems such as a desktop PC. Information can be written and erased in this type of memory a very large number of times. In the smart card chip, however, a RAM memory cell is approximately four times larger than an EEPROM memory cell.

RAM is also volatile memory; that is, the contents of the memory are lost when power is removed from the memory cell. So information in RAM is not preserved across a power-down and power-up cycle on a smart card. RAM is, nevertheless, essential for certain operations in smart card applications; in particular, it requires much less time for RAM locations to be read or written by the chip"s processor unit.

This can be extremely important when the smart card is interacting with a PC application in which the timing of responses from the card to the PC are important; this is often the case in the mobile telecommunications area (i.e., smart card-based cellular telephones).

The net result is that smart card chips tend to make use of varying amounts of each memory type depending on the specific application for which the smart card is intended to be used. The most powerful chips used in smart cards today have RAM sizes in the 1-kB to 2-kB range, ROM sizes in the 16-kB to 96-kB range, and EEPROM sizes in the 8-kB to 64-kB range..

Copyright © barcodefield.com . All rights reserved.