What is computer memory
Imagine your computer is like a brain, and just like our brains remember things, computers have
something called "memory" that helps them remember stuff too. Computer memory is like a bunch of
little storage spaces where the computer stores information it needs to work with.
Alu, input unit, main memory, secondary memory, control unit, output unit
1. Alu (arithmetic logic unit): this is like the math brain of the computer. It helps the computer do
all sorts of math and logical operations, like adding numbers, comparing if things are equal or not,
and making decisions.
2. Input unit: think of this like the computer's ears and eyes. It's how the computer gets information
from you. When you type on the keyboard, move the mouse, or plug in a device like a camera, the
input unit makes sure the computer understands what you're doing.
3. Main memory: this is the computer's short-term memory. It's like a desk where the computer puts
things it's currently working on. When you open a program or file, it goes into the main memory
so the computer can use it quickly.
4. Secondary memory: imagine this as the computer's long-term memory. It's like a big closet where
the computer stores things it doesn't need to use right away. Your pictures, videos, and files are
usually kept here. Even when you turn off the computer, the stuff in secondary memory stays safe.
5. Control unit: this is like the computer's manager. It directs all the other parts to work together. It
tells the alu to do math, the memory where to store things, and manages how data moves around
inside the computer.
6. Output unit: think of this like the computer's mouth and hands. It helps the computer show you
results. When you see things on the screen, hear sounds, or get something printed, that's the output
unit working.
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Storage evaluation criteria > memory capacity
Imagine your computer's memory like a backpack. The memory capacity is like how many things that
backpack can hold. If the backpack has a big capacity, you can put lots of toys, snacks, and books
inside.
Similarly, in a computer, memory capacity is about how many pieces of information it can hold at one
time. If the memory has a high capacity, the computer can remember and work with lots of programs
and files without feeling overwhelmed. It's like having a super spacious backpack that can hold
everything you need for your adventures in the digital world.
***units of memory capacity in number
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Storage evaluation criteria > access time
Access time is like the time it takes for your computer to find and use a piece of information it has
stored. Imagine you have a toy box with lots of different toys inside. When you want a specific toy,
you need to open the box, look inside, and find the toy you want to play with.
Similarly, when your computer needs to use something from its memory, like a picture or a program,
it takes a little bit of time to find and bring that information to where it can use it. This time is called
"access time."
Faster access time is like having a toy box where the toys are super organized and easy to find. You
can quickly reach in and grab the toy you want. Slower access time is like a messy toy box where you
have to search around a bit before you find what you're looking for.
So, access time is about how quickly your computer can find and use the stuff it needs from its memory.
Just like finding your favourite toy in a toy box!
Access time = seek + latency + reading/writing time
1. Seek time: imagine your computer's storage, like a hard drive, is like a library with many
shelves. When you ask the computer to find a specific piece of information, like a book in the
library, it needs to move its "reading head" to the right shelf where the information is stored.
Seek time is the time it takes for this reading head to move to the correct spot. Just like it takes
a little time for you to walk over to the right bookshelf in a library to find a book.
2. Latency time: now, let's say you've reached the right shelf with the book you want. But the
book isn't magically open in front of you. You still need to wait for the book to be in the right
position for you to read it. Similarly, in a computer's storage, when you've reached the right
location, you might have to wait a tiny bit for the specific information to come under the reading
head. This waiting time is called latency time. It's like waiting a moment for the pages of the
book to turn open in front of you.
3. Reading/writing time: once you've found the book, you read or write the information. This is
how fast you can get the information from the storage and use it. It's like how quickly you can
read the pages of the book once you have it in your hands.
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Storage evaluation criteria > cost per of storage
Think about buying a bunch of toy boxes to store your toys. Each toy box has a price tag. The "cost
per storage" is like figuring out how much you're paying for each toy box's space. If you have a lot of
toys and need a few big boxes, the cost per storage might be lower because you're dividing the cost
among more toys.
In the world of computers, it's similar. You're buying space to store your digital stuff, like photos,
videos, and files. The cost per storage tells you how much you're paying for each unit of space. If you
get a bigger storage drive (like a hard drive or a cloud storage plan), the cost per storage might be
lower because you're spreading the cost over more space.
So, "cost per storage" helps you figure out if you're getting a good deal for the amount of space you're
getting to keep your digital things. It's like comparing how much you're paying for each toy box you
need to keep your toys organized. Lower cost is expected.
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Storage evaluation criteria > memory access
Type of memory access
Random access: imagine you have a toy box with lots of different toys inside. Now, let's say you can
instantly pick any toy you want from the box, no matter where it's located. That's what we call "random
access."
In computers, it's like having a magical toy box where you can reach in and grab any piece of
information you need right away, without going through all the other information first. This is really
helpful because it means you can get to your stuff quickly, just like finding your favourite toy in your
magical toy box without having to dig through everything else.
So, "random access" in computers is like having a super-fast way to find and use any piece of
information, kind of like how you can quickly pick out any toy you want from your special toy box.
Sequential access: imagine you have a storybook with pages full of different stories. When you read
the book from the beginning to the end, following one story after another, you're using "sequential
access." you go through the pages in order, like following a path step by step.
In computers, sequential access is similar. It's like going through information in a straight line, one
after another. If you're looking for something specific, you might have to start at the beginning and
keep going until you find it. It's a bit like flipping through the pages of your storybook until you find
the story you're looking for.
However, it can be slower if you're searching for something in the middle of a long list, just like
needing to read through the stories before the one you want in the book. So, "sequential access" is like
following a path or reading through information one step at a time, like going through the pages of a
book in order.
Volatile memory, non-volatile memory, memory address, memory word
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Volatile memory: memory that forgets when the power is turned off, like a whiteboard that erases
when you close it.
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Non-volatile memory: memory that remembers even when the power is off
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Memory address: a unique label that helps the computer find information in its memory, like a
house address guiding you to a specific place.
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Memory word: a chunk of information that the computer handles together, like a puzzle piece in
a larger picture of data.
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Destructive memory: memory that changes by erasing or replacing the original information.
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Non-destructive memory: memory that changes without erasing or damaging the original
information.
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Memory store/write: putting things into a computer's memory so it can remember them, just like
putting your toys in a box to remember where they are.

Memory read: taking things out of a computer's memory to see or use them, similar to reading a
book to understand the words on its pages.
1. Volatile memory: imagine a whiteboard where you can write down important things, but as soon
as you turn off the lights, everything you wrote disappears. Volatile memory is like that. It's a type
of computer memory that holds onto information only as long as the computer is turned on. When
you turn off the computer, the information stored in volatile memory disappears.
2. Non-volatile memory: now think of a special notebook where your writings stay even when you
close the book. Non-volatile memory is like that. It's a type of memory that can keep information
even when the computer is turned off. Your photos, documents, and important stuff are usually
stored in non-volatile memory so they don't disappear when the computer takes a rest.
3. Memory address: imagine a street address for your house. It helps people find your place. A
memory address is like that but for the computer's memory. Each tiny space in the computer's
memory has a unique address. This helps the computer find where it put certain information, just
like you can find a specific house using its address.
4. Memory word: think of a puzzle piece with a word written on it. A memory word is like that
puzzle piece. It's a chunk of information that the computer deals with at once. Computers usually
process information in groups of memory words, like reading a bunch of puzzle pieces that fit
together to make a whole picture.
Imagine you're building a puzzle with big, colourful pieces. Each of these puzzle pieces has a letter
or a picture on it. Now, when you put a few puzzle pieces together, they start to form a word. In a
similar way, a "memory word" in a computer is like a group of pieces of information that fit
together and make sense to the computer.
Think of these memory words as building blocks that the computer uses to understand and work
with information. Instead of dealing with every tiny piece of data separately, the computer groups
them into memory words, making it easier to handle and process. It's like putting together puzzle
pieces to create a clear picture of what's going on in the computer's mind. So, a memory word is
like a bunch of puzzle pieces that hold information and help the computer figure things out, much
like putting together parts of a puzzle to see the bigger picture.
5. Destructive memory: imagine you have a sandcastle you're building at the beach. If you decide
to reshape the sandcastle into a new design, the old shape gets destroyed. Similarly, "destructive
memory" is like making changes to something that erase or replace what was there before. In
computers, when you work with destructive memory, the changes you make can remove or
overwrite the original information. It's like changing the sandcastle's shape and losing the old one.
6. Non-destructive memory: think of using sticky notes on a board. You can write or draw on these
notes and then move them around without damaging them. "non-destructive memory" is similar.
It's memory that lets you make changes without erasing or damaging the original information. In
computers, working with non-destructive memory means you can modify things without losing the
previous data. It's like rearranging sticky notes without tearing them up.
7. Memory store/write: imagine you have a special box where you can keep your favorite toys.
When you put a toy inside the box, you're "storing" or "writing" it there. In a computer, it's like
saving a picture, a song, or some information in its memory. When you store or write something,
the computer keeps it safe so you can use it later, even after you turn off the computer.
8. Memory read: think of a book in a library. When you open the book and read the words, you're
"reading" the information in it. Similarly, in a computer, "reading" means getting the stored
information from its memory. For example, when you open a file or look at a picture, the computer
"reads" the data and shows it to you on the screen. It's like flipping through the pages of a book to
understand what's written inside.
Classification of memory
1. Internal processor memory:
Imagine you have a small notepad next to you where you jot down quick notes while you work.
The "internal processor memory" is like that notepad for the computer. It's a tiny space right inside
the processor where the computer stores information it's using right now. Just like your notepad
helps you keep track of important things, this memory helps the computer work on tasks.
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Registers: imagine you have a small shelf right next to your desk where you keep your
most important tools – like a pen, calculator, and sticky notes. These tools are super handy
because they're right there when you need them. In a computer, "registers" are similar.
They're tiny, super-fast memory spaces inside the processor that hold the most important
data the computer is using right now. Just like you keep your essential tools nearby, a
computer keeps its vital information in registers for quick access.
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Cache memory: think about having a special drawer in your desk where you keep things
you use often, like your favourite snacks. This drawer is closer to you than the bigger
closet across the room. In a computer, "cache memory" is like that drawer. It's a faster and
smaller memory space than the main memory, and it holds frequently used data so the
computer can get to it quickly. Just as you keep your favourite snacks in the easy-to-reach
drawer, a computer stores important stuff in cache memory to speed up its tasks.
2. Main memory:
Think of a big table where you put things you need while you're working. The "main memory" of a
computer is similar. It's a large space where the computer keeps programs and data that it's currently
using. When you're using software or opening files, the information is stored in the main memory
so the computer can access it quickly, like having your tools on the table while you're working.
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Ram (random access memory): imagine you have a big table where you can spread out
all your toys and play with them. Ram is like that table for your computer. It's a space
where your computer can quickly put things it's using right now, like a game you're
playing or a document you're working on. Ram helps the computer work faster because it
can easily reach and use the stuff it needs. However, just like your table doesn't keep things
forever, ram forgets everything when the computer is turned off.
A place in a computer where it quickly stores and uses information while it's working, like
a temporary workspace. Ram helps the computer work faster, but it forgets everything
when the computer is turned off.
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Static ram (sram): imagine you have a whiteboard where you draw pictures,
and they stay exactly as you drew them until you decide to erase them. Static
ram is similar. It's a type of computer memory that can remember things without
needing a constant refresh. When your computer needs to use information
quickly, it turns to sram. It's like having a whiteboard where your drawings stay
clear until you change them.
Fast memory that remembers without needing constant refreshing.
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Dynamic ram (dram): think of a snowflake that melts away if you don't keep
it cold. Dynamic ram is kind of like that – it needs to be refreshed regularly to
keep the data alive. It's another type of computer memory that can store a lot of
information, but it's not as quick as sram. It's like having a snowflake that you
need to keep from melting by giving it a little chill every now and then.
Memory that needs regular refreshing to keep data alive.
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Rom (read-only memory): think of a bookshelf where you keep special books that you
never need to change, like your favorite stories. Rom is like that bookshelf for your
computer. It stores important stuff that the computer needs to start up and work, like
instructions on how to begin. Unlike ram, rom doesn't forget when the computer is turned
off. It's like having a permanent shelf of information that's always there, even when the
power goes off.
A part of the computer's memory that holds important instructions and data that the
computer needs to start up and function. It keeps this information even when the computer
is turned off, acting like a permanent storage.
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Mask rom (read-only memory): imagine a special book with fixed pages that
you can't change. A mask rom is like that. It's a type of computer memory where
information is permanently set during manufacturing. It's like having a book where
the words are already printed, and you can't change them. Computers use mask
rom for essential instructions that never need to be updated, like a recipe that's
always the same. A memory with fixed information that can't be changed, like a
preprinted book.
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Prom (programmable read-only memory): think of a blank puzzle where you
can write things with a special pen. A prom is similar. It's a memory that you can
program once with your own data or instructions. Once you write on it, the
information stays there, just like a completed puzzle that doesn't change. Prom is
like having a puzzle where you can create your own picture, but once you've
placed the pieces, they can't be moved. A memory you can write on once, like a
puzzle that's completed and can't be changed.
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Eprom (erasable programmable read-only memory): imagine a whiteboard
where you can write something, erase it, and write something new. An eprom is
like that, but for computers. It's a memory you can program, erase, and then
reprogram with different information. You can change what's stored in it, but it
needs special uv light to erase the previous data. Eprom is like having a whiteboard
that you can write and rewrite on, but with a bit of a process to start over. A
memory you can erase with special light and reprogram, like a whiteboard that
needs a certain process to clear.
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Eeprom (electrically erasable programmable read-only memory): think of a
special notebook where you can write and erase things using a magical pen. An
eeprom is like that notebook. It's a memory that you can program and erase using
electricity, without any uv light. This makes it more convenient to use and
reprogram multiple times. Eeprom is like having a notebook where you can write,
erase, and rewrite things with ease. A memory you can erase and reprogram using
electricity, like a notebook with a magical pen for writing and erasing.
In simple words, mask rom is like a fixed book, prom is like a puzzle you can write
on once, eprom is like a whiteboard you can erase with uv light, and eeprom is
like a magical notebook that you can write and erase using electricity. These types
of memory help store different kinds of information in computers and devices.
3. Secondary memory:
Imagine you have a storage room at home where you keep things that you don't need all the time,
like old clothes or books. The "secondary memory" of a computer is like that storage room. It's a
much bigger space where the computer stores files, photos, videos, and other stuff for the long term.
Even when the computer is off, the information remains safe in this storage, just like your things in
the storage room at home.
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Hard drive: imagine a big storage room in your house where you keep all your toys,
books, and clothes. A hard drive is like that storage room for your computer. It's a box
inside your computer where you can store lots of files, pictures, and programs. It's like
having a big closet where you keep everything you want to use on your computer. The
hard drive can hold a ton of information, and it keeps your stuff safe even when you turn
off the computer.
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Cd (compact disc): think of a music player where you put a round disc to listen to your
favorite songs. A cd is similar. It's a flat, shiny disc that can hold a lot of information, like
music, pictures, or software. You can put a cd into your computer's cd player, and the
computer can read the information from it. It's like playing a story from a magic disc.

Floppy disk: picture a small box where you keep some small cards with important notes.
A floppy disk is a bit like that. It's a small, thin piece of plastic that stores data. In the past,
people used floppy disks to save their files and move them between computers. It's like
having a tiny pocket that holds important information you can carry around.
Flash memory and cache memory
1. Flash memory:
Imagine a tiny box where you keep your special treasures, and you can take it anywhere. Flash
memory is like that portable box for your computer. It's a kind of storage that can store lots of stuff
– like your photos, music, and apps. The cool part is, even when the computer is turned off, the
stuff stays inside, just like your treasures in the box. It's handy because you can take your flash
memory and use it in different devices, like moving your treasures to different places.
2. Cache memory:
Think of a super-fast but small desk drawer right next to you. You keep the things you're using
right now in this drawer, so you can quickly grab them. Cache memory is like that special drawer
for your computer. It's a small and super-speedy storage where the computer puts stuff it thinks
you'll need soon. When you're doing something on the computer, it uses the cache memory to work
really fast, like having your important tools right at your fingertips.
In simple words, flash memory is like a portable box for storing your important things, and cache
memory is like a quick-access drawer that the computer uses to speed up tasks. Both of these help
make your computer work efficiently!
Factors affecting ram speed
Here are the factors that can affect the speed of ram (random access memory):
1. Clock speed: ram operates at a certain speed known as its clock speed. Higher clock speeds mean
that the ram can perform more operations per second, which leads to faster data access and
processing.
2. Memory type: different types of ram, such as ddr3, ddr4, and ddr5, have varying speeds and
capabilities. Newer generations of ram generally offer faster speeds compared to older ones.
3. Memory channels: some computer systems use multiple memory channels to access ram
simultaneously. This can boost data transfer rates and improve overall system performance.
4. Memory timings: ram modules have timing values that determine how quickly they can respond
to requests. Lower timing values generally indicate faster responsiveness.
5. Cache latency: the time it takes for data to be transferred from the ram to the processor's cache
memory can impact overall system performance.
6. Bus speed: the speed at which the computer's memory bus operates affects how quickly data can
be transferred between ram and the processor.
7. Processor compatibility: the compatibility and synchronization between the ram and the processor
can affect how efficiently data is transferred and processed.
Explain memory hierarchy
Here's a breakdown of the memory hierarchy layers:
1. Registers: these are the fastest but smallest memory units, located inside the cpu. Registers store
the data that the cpu is actively working with, ensuring lightning-fast access.
2. Cache memory: this memory is faster than main memory but smaller in capacity. There are usually
multiple levels of cache (l1, l2, l3), each progressively larger and slightly slower. Cache stores
frequently used data to reduce the time the cpu spends waiting for information.
3. Main memory (ram): this is larger in capacity than cache memory but slightly slower. Ram holds
programs and data that are currently being used or processed by the computer. It's faster than
secondary storage but more expensive.
4. Secondary storage: this includes devices like hard drives (hdds) and solid-state drives (ssds).
Secondary storage has larger capacity but is slower than ram. It's used to store data and programs
when they're not actively being used.
5. Tertiary storage: this can include external storage devices like usb drives or network-attached
storage (nas). While slower than secondary storage, tertiary storage provides additional capacity
for less frequently accessed data.
The memory hierarchy is designed to optimize the trade-offs between speed, capacity, and cost.
The faster and smaller memories are used for quick data access and processing, while the larger
and slower memories store more data at a more affordable cost. The computer's control system
manages data movement between these layers, ensuring that the most relevant data is readily
available to the cpu while efficiently managing storage needs.