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Applied IT (Year 11) - Hardware (U1)

Jeckmen Wu

The Purpose of Memory vs. Storage

Memory temporarily houses short-term data and instructions that the CPU processes to load applications or files. Storage, on the other hand, is more long-term as it is designated to the permanent storage of data, such as documents and media.

Primary Memory 

Primary memory is located on the motherboard and directly accessible by the CPU, making it extremely fast to store and retrieve data from it. However, it is “volatile”, as the information stored on it will be deleted once the computer is turned off. 

Primary memory consists of RAM (Random Access Memory), ROM (Read Only Memory) and Cache:

  • RAM – used to load applications and temporarily store commands. When the application closes, the operating system will remove any associated data from the RAM to free up space for another application. Thus, RAM size will dictate how many applications your computer can open simultaneously (as more applications mean more instructions) while still running fluently. 

  • ROM – its primary purpose is to store a software called the BIOS (Basic Input Output System) which includes instructions necessary to start-up the computer. In order to execute this function, the ROM will need to be non-volatile (data is retained even when the computer is off), making it quite unique as a primary non-volatile memory. As suggested by the name, the ROM can only be “read” and cannot be modified or erased due to the integral role it plays in the basic operation of the computer.

  • Cache – serves a similar purpose to RAM in terms of storing commands. However, where they differ is that cache will also hold copies of program instructions that are most frequently used by the CPU. This optimises efficiency as those instructions can be retrieved by the CPU a lot faster due to the close proximity between the cache and the CPU – positioned either on the CPU itself or in very close vicinity of it. 

Secondary Memory 

Secondary memory is not located on the motherboard but is still indirectly connected to it through cables. Since it is dedicated to storing large amounts of data permanently (i.e. non-volatile), it tends to be significantly larger than primary memory; usually at least 128GB if not in excess of 256GB. Examples of secondary memory include HDD (Hard Disk Drive) and SSD (Solid State Drive).

A good analogy for cache, RAM and HDD is to think of the human body as the CPU, the cache as your hands, the RAM as your pockets, and HDD as your backpack. As the things in your hands are quickly and directly accessible, you would probably use it to hold something that you frequently use, such as your phone. However, since your hands can only hold a limited number of things at once, you will need pockets to store your other possessions. Things in your pockets are still easily accessible but not as quickly as the things that are already in your hands. This reflects the speed difference between a CPU retrieving data from the cache vs. the RAM, as well as their capacity difference. However, when your pockets are full, a backpack will be required to store your extra possessions. Accessing things from your backpack will obviously be a lot slower, hence why the computer will start to slow down when the RAM is reaching full capacity as it is needing to temporarily direct the overflow of data from the RAM to the HDD (this is known as virtual memory). Therefore, with more pockets (i.e. more RAM), you can have easier access to more things at once (i.e. handle more tasks or applications) without resorting to your backpack (i.e. HDD).

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