Primary memory is a key component of a computer system that enables it to function. Primary is mainly made up of RAM and ROM. Each of these have different uses within the computer.
Definition
Primary memory, also known as main memory, is the component of the computer that holds data, programs and instructions that are currently in use.
Primary storage is located on the motherboard. When programs are being run data is read from and written to primary memory. Primary memory is designed such that the processor has fast access to the data and instructions.
Different types of primary memory
Read Only Memory
Read Only Memory, ROM in short, is a type of memory that can be read from but cannot be written to. This memory is non-volatile meaning that the data in ROM remains there when the computer is switched off.
Computers do not usually come with a lot of ROM. Only a small amount is necessary to store the most basic hard-coded instructions and data for the computer to boot-up and load the operating system. Such instructions are written to manually by the manufacturer and cannot be erased!
ROM will contain the following data and programs for the computer to boot-up properly:
Basic Input Output System aka BIOS This program checks that the hardware and the system's main input-output interfaces are functioning. Without it, the computer will not work. All computers need this so it will always be in ROM.
Bootstrap Loader The program that loads the OS from your disk onto RAM, which is up next!
Random Access Memory
Random Access Memory, RAM in short, is a type of memory that can be read from and can be written to by the processor. This memory is volatile, meaning that the contents of this memory is flushed when the computer is switched off.
Modern computers come with a generous amount of RAM because it is used to hold the data and instructions that are currently being processed by the CPU. And we put our computers to a lot of work.
Whilst your computer is on, the programs all the you are running; the files that you are currently editing; the playlist you are listening to, and the operating system are all kept in RAM. In fact, RAM is also commonly referred to as working memory and even Dynamic RAM since it is the memory that is used the most when the computer is working.
Cache Memory
Even though Dynamic RAM is pretty fast it does not come close to the speed of the processor. Moreover, getting data and instructions from DRAM to the processor takes time. For the best user experience, it is important to keep the processor busy at all times.
For this reason we have another type of RAM which is Static RAM which is commonly referred to as cache memory. This is a type of high-speed memory that is built into the processor so that data and instructions can be processed much quicker. The more cache a processor has the faster the computer can run. Remember, this memory is still considered as part of RAM therefore it is volatile.
However, there is a small catch, SRAM is much more expensive then DRAM. Moreover, too much of a good thing can actually be counter productive. Therefore we can only afford to use a small amount of cache memory to hold data and instructions that the processor is likely to reuse. Like this, processing performance is optimised because if the data required is in SRAM already then there is no need to wait for data and instructions to be fetched from DRAM.
Memory size matters
In Chapter 3 we had studied the following table in order to be able to talk about specific sizes of memory. To refresh your memory, we included the table in the card below.
How much ROM and RAM should be in a computer? Well... it depends the kind of computer of course. Just so you get an idea normal laptops usually contain:
Memory Type | Average Amount |
ROM | 4 MB to 8 MB |
DRAM | 4GB to 32GB |
L1 SRAM | Up to 4 MB |
L2 SRAM | Up to 8 MB |
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