The RAMs which are available at present are formed with Integrated Circuits (ICs) and data will be given in any order. So, we can’t call modern DRAM as random access. The different kinds of RAM such as DRAM, SRAM, ROM, OTP, NOR flash memory are all called as random access. RAM as said is mostly a temporary memory and data in it will be wiped when the power supply is off. But there are permanent memory RAMs as well such as ROM, NOR flash memory etc for instance.
At first RAM was manufactured in the year 1951. It was in use up to 1970. In later times, magnetic tapes, discs like memory designs came into use. The writable RAM manufactured between 1955 to 1975 was called as magnetic core memory. It was in use till the static and dynamic integrated RAM circuit was manufactured. These came into use in the period between 1960, 1970. Prior to these, for main memory in computers, relays, delay line / delay memory, vacuum tube instruments were being used. At present, strong RAMs are being manufactured using ICs.
Kinds of RAM
We can divide the present modern RAM as two kinds. Among these one is Static RAM (SRAM) and the second is Dynamic RAM (DRAM). In SRAM one bit data will be stored in Flip Flop. This type of RAM is more expensive. But it will work speedily and consumption of electricity is also less. It is used as cache memory for CPU in computers. In DRAM, data will be stored using transistors and capacitors together and is less expensive. So, this kind of RAMs are being used more at present in computers.
SRAM and DRAM are not permanent memories. The data will be wiped out when the power supply is off. The data will remain forever in the memory RAM which is in the motherboard. We can only read the data in it but can’t write. It is called as permanent memory. In ROM also writable ROM is available. In these ROMs it will have the properties of RAM & ROM because of which the data will remain stored. Even when there is no power supply, the data will not be deleted. This kind of memories are better called as USB flash drives. The memories which are used in portable devices and cameras will come under this category.
From the year 2007 NAND Flash came into existence changing the old storage like magnetic discs and tapes etc. The usage of NOR Flash began in place of ROM which is now used in Notebook PCs. There is a special circuit in SRAM & DRAM through which the memory errors are detected and corrected. CPU Registers, on-die SRAM caches, external caches, DRAM, paging, virtual memory and total system memory will be the master spell of computer. It is called “Memory Hierarchy” and all this together is called RAM. For installing and upgrading RAM easily, specially it is in the form of memory modules or DRAM modules.
Being a temporary storage, it will store which will run at present and retrieve. Also we can use it in many ways such as:
To utilize the RAM capability in present operating systems more adequately, the method called ‘Virtual Memory’ has been brought forth. Here virtual memory means, actually even though there is no memory additionally some memory will be shown by the operating system. It will get some portion in the hard drive as scratch partition or partition file. The RAM available already and scratch RAM will together act as total memory. For example if 2 GB RAM is existed and scratch partition (virtual memory) is 1 GB, the total memory in the system can be said as 3 GB. We have to do like this when the system is slow but make sure we should not have virtual memory more.
We can do partition of some portion in the RAM through software and can all it RAM disc as if hard disk.
At times, the contents of ROM chip to copy into RAM will take some time to access. This process is called shadowing. It will take place mainly in computers and embedded systems.