wer is not applied to the device. The embedded (nonvolatile) flash memory sits alongside (volatile but lower cost) SRAM (static random access) and DRAM memory (dynamic random access). Random access means just that, the memory is optimised for fast random access rather than steady sequential access. SRAM offers very fast read/write cycles (a few nanoseconds) but the data is held in volatile 'floating gate' (a volatile flip flop). It does not need refreshing as often as DRAM (hence the description static) but is still relatively power hungry. SRAM is used for temporary cache memory. DRAM memory holds data in a storage cell rather than a flip flop (which is why it is called dynamic). DRAM offers the lowest cost per bit of the available solid-state memories. A typical DRAM device will store up to 64 MB (512 Mb). SDRAM is synchronous DRAM - synchronous means the device synchronises itself with the CPU (central processing unit). DRAM products are inherently power hungry in that the storage cells leak and require a periodic refresh to maintain the information stored in the device. There are techniques such as temperature-compensated refresh, partial array self-refresh and deep power down that help reduce power drain. These products are sometimes described as mobile DRAM or mobile SDRAM. The volatility and related power-drain issues of these devices and their optimisation for random rather than sequential access makes them unsuitable for storing large amounts of video requiring sequential access. It has therefore now become increasingly common to supplement embedded memory with plug-in memory. Most plug-in memory consists of a NAND flash device (or multiple devices) on a die with a dedicated microcontroller. In the context of a cellular handset, plug-in memory can be summarised in terms of when the technology was introduced. 9.5.2 FLASH Based Plug-In Memory - The SIM card as an Example 9.5.2.1 The SIM Card The SIM card (subscriber identity module) became an integral part of the GSM specification process in the mid to lat