HP Pavilion Desktop Slimline s3421p Compatible Accessories

100% HP Compatible Upgrades from the UK's Leading Supplier of Memory & SSDs

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Model Specifications 161,437 HP Upgrades Supplied

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HP Pavilion Desktop Slimline s3421p

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We help people to feel safe, happy and secure. You can trust the Mr Memory brand - we will protect your data, save you money and improve the performance of your valued devices, whilst being eco-responsible.

Our specialists provide free support to anyone who needs it - at any stage of the order process. Our communication is fast and our guidance is as technical or as basic as you need it to be.

Buy from a UK based company with 32 years experience
100% Safe & Secure website
Fully informed at every stage of the order
Fast dispatch - 98% of orders dispatched same day
Highest quality brand new products from the best brands in the world
RAM extensively tested prior to shipment
Accurate database with new models added daily
30-day credit available to the Public / Private Sector
250,000+ businesses use Mr Memory for their Memory/RAM & SSD upgrades
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Mr Memory is tackling climate change as a team with an aim to being carbon neutral by 2027.

Our employees are encouraged to walk, cycle or car share
We encourage our employees to stay healthy, eat more sustainable food and buy locally
We always try to purchase from UK based companies where possible
We hold regular staff meetings where our employees opinions on climate change are heard
We supply appropriate uniform to reduce heating and air-con use
We have waste reduction procedures in place - all of our packaging can be recycled
Our refuse bags are bio-degradable
Our cleaning equipment and products are all eco-friendly
Our printing is limited to essential customer paperwork only
When not in use all electrical devices are turned off and we always purchase energy efficient devices
Our energy supplier is moving to 100% renewable electricity and is a COP29 Principal Partner
All of our suppliers use recyclable packaging, which we reuse where possible
We are constantly reviewing our Sustainability Statement

Trusted & Reliable Customer Reviews

Good service

Great after care when we had an issue

Chris - Friday 22nd May 2026

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Mr Memory was very helpful all the time

M. Bran - Tuesday 19th May 2026

Verified order

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Items arrive quickly and well packaged

Items arrive quickly and well packaged. Bought from Mr Memory 4 or 5 times over past few years. Always great customer support.

Sharon E - Monday 4th May 2026

Verified order

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First Class all round!

I don't use Mr Memory frequently but have bought from them for many years when upgrading my (and extended friends and family's) various computers or replacing hard drives. I have never had cause to contact them outside of the normal process because a) everything has always been spot on and b) I haven't been a numpty before and ordered the wrong thing! So the most recent transaction with them has been a wholly enjoyable experience and totally different from any other contact I have had with any other company.
I ordered PC memory, when I should have ordered laptop memory -totally my fault! - and upon completing the returns details (which is all free post by the way!) I received an email from a wonderful person named Zoe, who happens to be Head of Operations, within 30 minutes giving me a return reference and asking what I wanted to exchange it for (the return request was for replacement not refund).
I replied with my brain fart issue and stated the laptop memory needed.
I received a very fast reply stating the laptop memory will not be in stock until the following Monday.
I then - being the awkward customer I am - asked if it could be posted to a different address as I was on a bit of a time crunch. Zoe replied saying it wouldn't be a problem. I then asked how I could pay the (very small amount) difference..... and she replied saying that they wouldn't charge any more than I had already paid!
If anyone out there doesn't agree about the absolute first class customer focus and service after hearing all my issues and stupidity that Zoe dealt with....
I have no words!
Thank you Zoe and Mr Memory, I am very glad I purchase hardware from you and will continue to do so!

HSP - Friday 24th April 2026

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4.9 out of 5 MORE REVIEWS