This technical report will look at various different memory devices and how they are implemented in a standard computer system. Internal memory devices such as ROM, PROM, RAM, SRAM, DRAM, SIMM and DIMM will be looked

Random Access Memory

Memory comes in two types, one of which has just been looked at (i.e. ROM and the different types of ROM) and other which is known as RAM (Random-Access Memory). RAM means that any memory location can be directly accessed by referring to its address. Data and programs are transferred into and out of RAM, and this data in RAM is processed according to the instructions in the program. RAM is much faster to read from and write to than all the other kinds of storage in a computer system i.e. the hard disk, CD-ROM and floppy disk. The data held in RAM stays there for the duration the computer is running and when the computer system is switched off, RAM loses all its data. Once the computer is switched on and booted up again, the operating system and/or other files are re-loaded into RAM (these are usually loaded from the hard disk). RAM holds a key resemblance to the short-term memory of a human in that it concentrates on the task in hand, but can only hold a limited amount of data at any one time. If RAM is fully used up, the CPU of the computer system needs to constantly go to the hard disk to place on top old data in RAM with new data, which makes this an extremely time consuming process. One of the advantages of RAM is that no matter how much data is fed into it, it never runs out of memory, as oppose to a hard disk, which cannot accept any more data once it becomes full. The more data that is held in RAM, the slower it operates.

Static RAM and Dynamic RAM

One type of RAM is SRAM (Static Random Access Memory). SRAM retains its information as long as the power of the computer system is switched on. This memory is used for a computers cache memory, and as part of the “Random Access Memory Digital to Analogue Converter” on a video card.

Another type of RAM is DRAM (Dynamic Random Access Memory). This memory is the most common kind of RAM used in standard computer systems. DRAM stores each bit in a storage cell, which is made up of a transistor and a capacitor. Capacitors tend to lose their charge quite quickly, therefore need to be recharged.

DRAM chips are smaller and simpler in design compared to SRAM chips, but they are generally slower in operation, which makes the information slowly leak away and has to be refreshed (unlike Static RAM) by special regenerator circuits located in the CPU. The main memory of most computers uses Dynamic RAM chips, with the more expensive and faster Static RAM being used as cache memory. Both these types of memory lose all information as soon as the power of the computer system is switched off. Static RAM generally does not need refreshing as it operates on the principle of moving current that is switched in one of two directions rather than a storage cell that holds a charge in place.

Single In-Line Memory Module and Dual In-Line Memory Module

A SIMM (Single In-Line Memory Module) is a module which holds one or more random access memory chips on a small circuit board, whereby the pins of these chip connect directly to the motherboard of the computer system. SIMM’s are commonly manufactured with a 32 data-bit (36 bits including parity bits) path to the computer, which usually requires a 72-pin connector. SIMM’s usually come in memory chip multiples of four megabytes. The higher value of RAM a computer has, the less frequently it accesses the secondary storage (for instance, CD-ROM or floppy disk). RAM can be increased by installing extra SIMM’s on a computer system, a practice which is highly commonplace. On a SIMM, the memory chips are usually Dynamic RAM chips (sometimes, an improved form of RAM called Synchronous Dynamic RAM can also be used). Because this provides a 64 data bit path to the computer system, it requires at least two SIMM’s or what’s more commonly known as a DIMM.

A DIMM (Dual In-Line Memory Module) is a double SIMM. Like a SIMM, it's a module containing one or more RAM chips on a small circuit board with pins that directly connect it to the computer system’s motherboard. For synchronous dynamic RAM (SDRAM) chips, which have a 64 data bit connection to the computer, SIMMs must be installed in in-line pairs (since each supports a 32 bit path). Synchronous Dynamic RAM chips have a 64 data-bit path which connects to the computer system, therefore requiring two SIMM’s. However, a single DIMM can be used instead, which has a 168-pin connector and can support a 64 bit data transfer. With DIMM’s, you can install an entire memory medium via one DIMM at a time.

Memory Stick

A Memory Stick is a digital data storage technology which can hold up to 10 times more data compared to a standard 3.5” floppy disk (which can stored up to 1.44MB of data). This device has become a new way to share and transfer pictures, sound, video and other data between different compact electronic devices such as camcorders and the latest hand-held digital cameras. Memory Sticks are physically very small in size, and typical models have storage capacities which range from 2MB to 128MB. They are designed with ergonomics in mind, in that they are smaller than most flash memory devices and other devices of similar nature. A Memory Stick is commonly seen as a small, flat, rectangular card that contains memory chips. They fit into memory stick slots on computer systems, digital cameras, digital camcorders, wireless phones and other electronic devices. This device also has a lock mechanism to prevent the erasure of data.

Uses of Memory Devices in Multimedia Technology

Memory devices have become an integral part of technology in multimedia. For example, Read-Only memory is very commonly used in mobile phone technology. When the ROM chip of a mobile phone is manufactured, data such as its unique serial code, creation date, warranty expiration date, purchase date and phone version values are burnt in. This data cannot be modified by the user and it can be lost if the mobile phone is switched off. Random Access Memory is also implemented in mobile phone technology via the introduction of “phone games,” whereby the user controls how the game is played. When the user sends an instruction to the phone (whilst playing a game), the memory location which executes that particular instruction can be directly accessed by referring to its address. Typically, DRAM chips are used in mobile phone technology, as they are cheaper and smaller in size compared to DRAM chips.

How a Memory Device can be used in a Multimedia System

A memory device such as Flash Memory can be used in various different ways in a multimedia system. For example, flash memory can be used to copy and transfer picture files from one digital camera to another or from a digital camera to a standard computer system.  Once the flash memory stick is placed into the slot which is provided on the digital camera itself, each photo that is taken is directly stored on this device. Any picture files which have been generated on this device can then be transferred by removing the Flash Memory and inserting it into another digital camera, whereby the user has the option of storing selected picture files into the camera’s “hard disk” memory. The quality of the images do not get distorted, rather they are preserved to maintain their optimal overview. Furthermore, the Flash Memory can also be used to transfer pictures onto a standard computer system, where the user can print, edit or save files directly on to the default memory device.

Conclusion

Now that all the various memory devices have been analysed, appropriate conclusions will be drawn up in order to sum up what has been discussed. Internal memory devices such as RAM, ROM (and all the branches of ROM), SIMM’s and DIMM’s are requisites of a computer system. Without such memory devices, a computer system cannot function and there would be no storage medium to hold temporary data and data which instructs the operating system function correctly. External memory devices such as Memory Sticks and Flash Memory devices have become a way of replacing their predecessors (i.e. floppy disk and CD-ROM), and are not really required by a computer system in order for it function correctly. They are mainly used as a convenience and as a way of transferring data from one medium to another with minimal hassle. Such devices have also been incorporated into multimedia devices such as MP3 players and digital cameras, a “craze” which is becoming increasingly popular.