Welcome to the ITFreeTraining video on the basics of how Random Access Memory or RAM works. Since RAM was first created, there have been major changes in how it operates. Having an understanding of how RAM works will give you an idea of what to expect from different RAM types.

Download the PDF handout: http://itfreetraining.com/handouts/ap/3a04.pdf

What is Random Access Memory (RAM)?
0:18 So, what is RAM? RAM is essentially a form of storage that holds data and machine code. The difference from other types of storage is that RAM is currently in use by the computer and thus needs to be fast. By fast I mean, the speed of RAM is measured in milliseconds.

Inside your computer is a motherboard. This motherboard will contain one or more memory modules. Memory modules are also commonly referred to as memory sticks or sticks of RAM. These memory modules hold the data and software the computer needs to operate.

On the memory module will be a number of chips called DRAM chips or Dynamic RAM chips. The DRAM chips are what holds the data. Although there are many DRAM chips and they have improved over the years, these DRAM chips are the same kind that you would find in your hardware devices or mobile devices.

Essentially any device that runs code and needs to store data will have some kind of memory in it. In small hardware devices, the memory is often soldered onto the printed circuit board or PCB. In most computers, the memory modules can be replaced. However, in some computers the memory will be soldered onto the PCB. To understand how modern memory works, I will first look at one of the first ways that memory was implemented.

Vacuum Tubes
1:42 One of the first methods of storing data in a computer was with the use of vacuum tubes, back in the 1940’s. A vacuum tube is essentially a glass tube with no air inside, just like a light globe. The glass tube contains a filament.

If the filament is connected to a power source, the filament heats up. Now consider that you have two wires connected to the vacuum tube. If power is applied to the left and the filament is active; power will be allowed to flow through to the right.

If power is applied, this essentially mean that the vacuum tube is in the ‘on’ state. Next consider what happens if I have a second vacuum tube in which the filament is not on. When power is applied, this time the power will not be allowed through. This is called the ‘off’ state.

What the vacuum tube allowed was for a basic switch to be created, which could be in the on or off state. Or to think of it another way, it could be one or zero. This is the basic concept of how a transistor works. Transistors are a fundamental part of electronics. To understand this better, let’s look at a different example.

Example
2:56 The basics of a transistor work like this; consider that you have a door that is connected to a button, a bit like what you may find in a puzzle style computer game. If the button is not being held down the door remains closed. However, if something were to press the button and hold the button down, the door would open and remain open until the button is released. If the button is no longer being held down, the door will close.

This is the basic fundamentals of how a transistor works. When multiple transistors are combined together, more complex results can be achieved. In order to store one bit of information you may think you only need one transistor. You also need to consider that you need a way of accessing the bit and changing the bit. To store a single bit and control functions can take four or more transistors depending on what method is used.

Nowadays, a computer CPU can contain over a billion transistors in a single chip, so using minimum of four transistors does not sound like a lot. However, if you consider a gigabyte of memory would be eight billion bits, now times this by four, this would give 32 billion transistors. You can start to understand why there is only a small amount of RAM in a CPU and the majority of the RAM is found on memory modules outside the CPU.

Video description to long for YouTube. Please see the following link for the rest of the description. http://itfreetraining.com/ap/3a04

References
“CompTIA A+ Certification Exam Guide Ninth Edition” pages 138-154
“Flash memory” https://en.wikipedia.org/wiki/Flash_memory
“Nano-RAM” https://en.wikipedia.org/wiki/Nano-RAM
“Memory cell (computing)” https://en.wikipedia.org/wiki/Memory_cell_(computing)
“Flash memory” https://en.wikipedia.org/wiki/Flash_memory

Credits
Trainer: Austin Mason http://ITFreeTraining.com
Voice Talent: HP Lewis http://hplewis.com
Quality Assurance: Brett Batson http://www.pbb-proofreading.uk

Exploring some of the basics of computer memory: latches, flip flops, and registers!

The simulation tool is now available to download:
https://sebastian.itch.io/digital-logic-sim
Source code for the simulator can be found here:
https://github.com/SebLague/Digital-Logic-Sim

If you’d like to support the creation of more videos (and get early access to new content), I’d greatly appreciate the support here: https://www.patreon.com/SebastianLague

See the full playlist here: https://www.youtube.com/playlist?list=PLFt_AvWsXl0dPhqVsKt1Ni_46ARyiCGSq

Resources and Inspiration:
https://www.youtube.com/c/BenEater
https://www.coursera.org/learn/build-a-computer
https://en.wikipedia.org/wiki/Flip-flop_(electronics)#SR_NOR_latch
https://en.wikipedia.org/wiki/Sequential_logic
https://electronics.stackexchange.com/questions/65463/why-edge-triggering-is-preferred-over-level-triggering
https://tams.informatik.uni-hamburg.de/applets/hades/webdemos/16-flipflops/20-dlatch/dff-enable.html

Chapters:
00:00 Intro
00:33 Set-Reset Latch
04:33 Data Latch
05:56 Race Condition!
07:32 Breadboard Data Latch
09:36 Asynchronous Register
11:41 The Clock
13:03 Edge Triggered Flip Flop
14:18 Synchronous Register
16:48 Testing 4-bit Registers
18:25 Outro

Music:
“Frontier” by Shimmer
“A Quiet Place” by Jordan White
“Constellations” by Acreage
“Beyond the Horizon” by Sounds Like Sander
“Crystal Bursts” by Cody Martin
“When Rain Comes” by Tide Electric
“Air” by Assaf Ayalon
“Mallets of Mischief” by Rhythm Scott

Images:
https://upload.wikimedia.org/wikipedia/commons/8/87/TTL_flip-flop.svg

Take the 2017 PBS Digital Studios Survey: http://surveymonkey.com/r/pbsds2017. Today we’re going to create memory! Using the basic logic gates we discussed in episode 3 we can build a circuit that stores a single bit of information, and then through some clever scaling (and of course many new levels of abstraction) we’ll show you how we can construct the modern random-access memory, or RAM, found in our computers today. RAM is the working memory of a computer. It holds the information that is being executed by the computer and as such is a crucial component for a computer to operate. Next week we’ll use this RAM, and the ALU we made last episode, to help us construct our CPU – the heart of a computer.

*CORRECTION*

In our 16×16 Latch Matrix graphic, we inadvertently left off the horizontal row access line above the top row of latches. As a result, the highlighted line for the row at address 12 should actually be one line higher.

Produced in collaboration with PBS Digital Studios: http://youtube.com/pbsdigitalstudios

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