RAM and ROM

Systems require storage units whether it was for short term or long term purposes. Computer systems take advantage of the memory systems they have, whether it was Random Access Memory (RAM), Read-Only Access Memory (ROM), or highly dense storage units like hard drives.

You might be thinking why we can’t have one storage unit for all. To put it simply, it’s because each system is specially designed to work efficiently for its function rather than carry out all the functions you desire.

Let’s take this article as an example of how you can be utilising those three storage compartments on your computer right now.

We’ll start from the beginning with Read Only Memory (ROM). Without ROM you couldn’t initiate your system to boot up, this is because ROM is where the firmware is placed by the manufacturer i.e. your systems instructions this can also be referred to as BIOS.

To open up this article you had to initiate a sequence of commands, one of them is opening up a browser. For this to happen, the computer system will have to make use of its short term memory, this is referred to as Random Access Memory (RAM). Despite it being for a number of seconds, sometimes even instantly depending on your computer specification, the loading time between clicking on a program and getting an interface that a user can see and use is the time your system is sending and receiving information from the RAM.

Lastly, once you complete reading this article, you might want to save it. When you press the save button, the article is saved into your hard drive, which is used for long term storage, moreover, this is because if goes to the RAM, and you shut down your computer, you will not see it when you reboot your computer. This is why RAM is considered to be volatile, as it’s only considered to be temporary storage for tasks and functions you require which can be modified, unlike ROM.

Computer architects are always trying to increase efficiency in our computer systems and how we store our content. Nowadays, the use of cloud computing is emerging, where you physically store your content on a server in various locations around the world, and they are accessible from the internet.

Though there are concerns over cloud computing such as data security, the longevity of a company (this rises bankruptcy issues as you pay for your services for cloud computing), and accessibility where the performance depends on how much a customer is willing to pay for WAN bandwidth.

What is RAM?

RAM = Random Access Memory

The earliest form of RAM dates back to the 1940s which is when the first computers emerged. Magnetic memory had relied on magnetised rings to store data in each ring. This incorporated very large installations as each ring was wired separated, and each one of these rings managed to store a “bit” of data, the direction of magnetisation indicated one or zero (binary form).

The penultimate breakthrough in computational memory came in around the 1970s with the innovation of solid state memory within integrated circuits.

These memory units had used very small transistors, allowing architects to build memory units that can withhold lots of information in a small amount of space.

Essentially, RAM is the computer system short term memory, which is the opposite of what your hard drive is (SSD). RAM is also considered to be “volatile” as it’s only used for temporary storage, meaning that the content will not be available if the system is shut down and rebooted.

RAM will temporarily store everything that is running on the system, whether if you are using a text editor, browser (cached), or an image editing tool.

The benefit of having RAM in a computer is that the CPU can fetch the information it requires rapidly rather than excavate through the solid state hard drive (SSD). Despite have SSD’s which are a lot faster nowadays, they are still much slower than RAM.

Architecture of RAM

Due to RAM architecture, the memory cells can be accessed for information from anywhere on the computer system.

This communication between different peripherals and RAM is achieved by data input and output lines, control lines which specify the direction of transfer, and address selection lines.

(A “word” is a unit that a machine uses when working with memory, i.e. 32bit machine, means the word is 32bits long)

(A “bit” is the basic unit of information in computing)

Read and Write Operations

RAM can perform two operations, they are read and write.

Read: A signal transferring out

Write: A signal transferring in

Once the RAM accepts one of these control units, the internal circuits, which are situated inside the memory, provide the function, which is expected, from the user.

The process is:

1. The binary address of the required word is applied into the address lines
2. Apply the “data bits” that will be stored in memory into the data input lines
3. The write input will be activated
4. Once the steps above are complete, the memory unit will take the bits in the input data lines and will store them, specified by the address lines.

To transfer a stored word out of the memory unit the following occurs:

1. The binary address of the required word is applied into the address lines
2. Activate the read input (content of the word does not change after reading)

Lastly, the memory unit will take the “bits” from the “word” which was selected by the address, and apply them into the output data lines.

Types of RAM

Although there are quite a few types of RAM we will focus on the main three:

SRAM (Static Random Access Memory)

SRAM is a type of memory, which uses multiple transistors, usually around four to six. There is no capacitor (they act like batteries, they store electrical energy) in each cell and SRAM is used for caching.

Advantages include:

• Simplicity
• Performance
• Reliability
• Low idle power consumption

Disadvantages include:

• Density
• Price
• High operational power consumption

DRAM (Dynamic Random Access Memory)

The memory cells in this type of memory are paired with a transistor and a capacitor requiring constant refreshing.

Though it is more complicated than SRAM due to its complicated circuitry and timing requirements. The advantage of using DRAM is because of its memory cell structural simplicity. These units only require one capacitor and transistor per bit, compared to SRAM which requires 4-6. This makes DRAM less costly per bit.

VRAM (Video Random Access Memory)

This type of memory also known as “Multiport Dynamic Random Access Memory” (MPDRAM), is specially used for 3-D accelerators or video adapters.

The reason why it is also called “multiport” is that VRAM has two independent access ports instead of one. This allows the graphics processor and the CPU to access the memory unit simultaneously.

Resolution and colour depth is determined by the VRAM specifications on a device, furthermore, VRAM also holds graphic specific information like 3-D cemetery data and texture maps.

Most systems nowadays use SGRAM (synchronous graphics RAM), as it’s less costly and the performance is nearly the same.

Advantages of having RAM

• Increases the computer system speed, essentially, the more RAM a system has the faster it will operate.
• RAM is a component that is a mandatory to have in a system to allow for the storage of data, which will be processed by the CPU.
• It’s efficient. It’s extremely fast compared to hard drive storage for a CPU to read data from.
• It can write and read operations.
• RAM is power efficient.
• Cost less than SSD’s and operate faster than them.

Disadvantages of RAM:

• If CPU wants to read data only from the RAM, then the data access from the cache and the registers is slow in comparison to ROM.
• RAM is volatile, which means it is difficult to store data for a lengthy period of time. Unplanned circumstances like a power outage can result in data loss.
• It is expensive.

What is ROM?

ROM = “Read Only Memory”

ROM is a non-volatile read only storage unit within electronic systems, however, with ROM, data that is stored inside the memory units cannot be electrically modified after the device has been manufactured, as it is hard wired. 

ROM is a type of memory, which is useful at storing information, which doesn’t change during its lifespan in the system, this is referred to as firmware.

Read only memory is memory, which is hard-wired, this can include a diode matrix, for instance, a system that cannot be electronically changed.

Architecture of ROM:

Information in the form of binary is stored permanently inside ROM by the manufacture, the information is injected in the form of bits. ROM consists of logic gates only, arranged in a way that they store specified bits.

Block structure:

• The unit consists of k input lines and n out lines.
• The k input lines take the input address from where we want to access the content of the ROM.
• Since the input lines are either 0 or 1 (binary form). The input lines can be referred to as 2^k total addresses and each of these addresses contains n bit of information, which will be given out as the output of the ROM. This is specified as 2^k x n ROM

Internal structure:

The internal structure consists of two components: the decoder and OR (logic) gates.

• The decoder is a combinational circuit. It is used to decode any encoded form like binary to understandable forms like decimal form. Within the ROM structure, the input into a decoder will be binary and the output will be represented in decimal form.
• All the OR logic gates will have outputs of the decoder as their input.

Types of ROM

ROM can be classified into the following:

MROM (Masked Read Only Memory)

• MROM is the original type of ROM, it is read only. Therefore this memory unit cannot be modified.

PROM (Programmable Read Only Memory):

• This type of ROM is one, which can be programmed once the chip has been created. However once the chip has been programmed, the information written is permanent and it cannot be erased or removed.

EPROM (Erasable Programmable Read Only Memory):

• This type of memory, which was developed in 1971 by Dov Frohman, can be reprogrammed only when exposed to ultraviolet light, otherwise it cannot be modified and therefore no new data can be saved. These types of chips are not commonly used anymore in computer systems, and their use has been replaced by EEPROM chips.

EEPROM (Electrically Erasable Programmable Read Only Memory) :

• This type of memory can be erased and reprogrammed only by using an electrical charge. EEPROM was developed in 1970 by George Perlegos when he was in Intel. The edge that EEPROM has, is that it can remember data when the system is powered off. EEPROM is considered to be more superior to PROM and EPROM. It is used for the BIOS (Basic input/output system which deals with hardware initialisation during the booting process) of computers designed after 1994.
• The use of EEPROM allows the computer system to update the BIOS without the need to open the computer system or remove any chips.

Advantages of ROM

• It is non-volatile, meaning data which was set by the manufacture will function as expected when device is turned on.
• Due to them being static, they don’t need a refreshing time.
• In comparison to RAM, the circuitry is simpler.
• Data can be stored permanently.

Disadvantages of ROM: (with most use cases of ROM)

• ROM is a read only memory unit, so it can’t be modified.
• If any changes are required, it’s not possible.

Summary and Facts

What is RAM?

Random Access Memory (RAM), is one of the most vital components of a computerised system, whether it was mobile phones, gaming consoles, smart phones etc. Without RAM, these devices will not be able to function at all, and if they can function it will be at a much slower rate, that what the user visualises will be a slideshow rather than a constant flow.

Types of RAM

• SRAM: Static Random Access Memory
• DRAM: Dynamic Random Access Memory
• VRAM: Video Random Access Memory

What is ROM?

ROM is a non-volatile read only storage unit within electronic systems, with ROM, data that is stored inside the memory units cannot be electrically modified after the device has been manufactured, as it is hard wired, and an example of ROM is firmware.  

Nowadays, ROM is essential for the devices that we use in our everyday life. While ROM was made as a Read only memory unit, some of them have been modified to allow users to make adjustments to suit their own preferences.

ROM is used in many appliances, such as microwaves, dishwashers, electrical grills, and smartphones, in essence, any device which needs to know how to work when it’s turned on, after being turned off.

Types of ROM

• MROM (Masked Read Only Memory)
• PROM (Programmable Read Only Memory)
• EPROM (Erasable Programmable Read Only Memory)
• EEPROM (Electrically Erasable Programmable Read Only Memory)

Advantages of RAM

The advantage of RAM in a system is essentially its speed, the more RAM a system has the faster the system will operate, this increases the system efficiency. Although SSD hard drives are quite fast nowadays, they’re still considerably slower than RAM.

Disadvantages of RAM

Despite RAM being less costly than SSD hard drives, they are still relatively expensive. RAM’s biggest downside is considered to be the fact that they are volatile, which means that it can’t store data after the system is shut down.

Advantages of ROM

The advantage of ROM is that it’s non volatile, which means data can be stored permanently, and they don’t require a refreshing time as they are static. This enables the circuitry of the element to be simple in comparison to RAM.

Disadvantages of ROM: (with most use cases of ROM)

A massive disadvantage of ROM is that it’s a read only unit, so this means that programmers cannot modify it, if any changes were required.

RAM vs. ROM

RAM	ROM
Random Access Memory	Read Only Memory
Volatile memory	Non volatile memory
If the system is turned off, the information will be deleted	If the system is turned off, the information it carries will still be on the memory, meaning that the system can retrieve it again when the system is switched on
Requires power to store data	Doesn’t require power to store data
RAM is a temporary storage unit to store files	ROM is used to store BIOS/Firmware/software, programs and instructions which don’t change
Chips often range from 1 to 256 GB	Chips often range from 4 to 8 MB
Available in two primary sizes	They can vary in size
Temporary memory	Permanent memory

References:

1. https://www.digitaltrends.com/computing/what-is-ram/
2. https://centralvalleycomputerparts.com/articles/-ram-explained/
3. https://www.studytonight.com/computer-architecture/random-access-memory
4. https://computer.howstuffworks.com/ram2.htm
5. https://uk.crucial.com/articles/about-memory/different-types-of-memory-explained
6. https://www.computerhope.com/issues/ch001361.htm
7. https://tijeii.wordpress.com/2017/02/17/characteristics-advantages-disadvantages-of-ram-memory/
8. https://t4tutorials.com/ram-types-of-ram-advantages-of-ram-shortcomings-of-ram/
9. https://am7s.com/what-is-rom/
10. https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-536.html
11. https://en.wikipedia.org/wiki/Dynamic_random-access_memory
12. https://tijeii.wordpress.com/2017/10/26/disadvantages-of-read-only-memory-rom/
13. https://www.classmate4u.com/ram-and-rom/