Slow disk speed on my Windows 7 desktop

I've been suffering with slow disk speed on my Windows 7 desktop.

It was a new HP desktop in 2010, running an i7-930 at 2.8 GHz, 8 GB of 1066 MHz RAM. It had a 1.5 TB C: drive, 500 GB D: drive (both SATA 3Gb/s).

The 1.5 TB drive eventually crashed and was replaced four years ago by a 1 TB WD Black. A local shop installed the drive, and they also reinstalled Windows.

It was after the drive replacement that I noticed some drive slowdown. And it seemed worse on C: than on D:. I've been living with it since. I don't remember whether the slowness was immediate, or happened later when lots of software was re-installed.

Despite that I was getting good speed numbers from Crystal Disk Mark. It makes me think that the AV is performing checks when I run software (and maybe when I copy files), but not when CDM is running its disk thrash activity? That would account for slow real-world performance, but respectable CDM measurements.

Anyway ... I had been running AVG anti-virus before, but it slowed down my piano VST software, causing dropouts. So I switched to Malwarebytes. The latter seemed lightweight, and did not cause dropouts.

Wind ahead three years ... and last month I got fed up with Malwarebytes. I guessed that maybe AVG has improved in these last years, so I installed the free version again. It worked well enough, but it kept nagging me that my 30 trial of "Internet Protection" would soon end.

I presumed that Internet Protection was some "extra" package at extra cost. One that I don't need. All I want is the active anti-virus part.

But no! Beginning this morning AVG completely stopped working. It says, basically, "pay or get out". (Now why does my wife's desktop NOT say that? She has AVG free, too.)

So I guessed that I had the wrong "free" version, and I downloaded a new one. I uninstalled the old, installed the new ... and it got stuck at 37% installed. I uninstalled and tried again ... and got stuck at 37%.

I found an online board in which AVG recommends their own .exe file to run the uninstall. I used that and tried again (this time with yet another, different AVG free version). This time I got stuck at 75%.

Dismayed at wasting so much of my early Sunday morning on this garbage, I sought a new AV.

I tried Avast free. It's installer doesn't give percentages. It just sits there with a scrollbar/worm sliding left and right and left and right ... forever and ever. It's stuck!

Kill. Try another! This time Avira. Installs fast and works. No problems. At last.

All of this long-winded blather might seem a lesson in pain with anti-virus software. But in fact, there's a portion that's MUCH more important to me ...

I found that disk access has improved way way much. My Kontakt music software loads in five seconds. I don't know what it was before, but it was WAY more.

Then when I load six pianos into Kontakt (about 1.5+ GB of digital audio data), they load in seconds. It used to take minutes.

And the only changes I'm aware of were dumping MWB and AVG, and installing Avira.

Were MWB and AVG really so bad that they slowed me down so much?

Hello margrave mate for starters I wouldn't touch AVG with a stick if were me. If Avira is ok with then keep it - personally when I tried it on my tester I really didn't think much of it.
If you ever want a change then see this.
If you want a good free AV then there are plenty in this
Free Windows Desktop Software Security List - Realtime Protection | Gizmo's Freeware
However I would advise you against using AVG, McAfee, Baidu, Ad-Adaware, and Comodo (only because it is a terrible nagger)
I have tested out Bitdefender, Avast,Avira, MSE, Sophos, and Panda and out of those I would if I were not using a paid for version of Kaspersky run Bitdefender, Avast, and Avira in that order and then the others. I mentioned the Kaspersky only because I have used it for a very long time now and as well as being an excellent AV is also very cheap to run at approx $0.035 a day (currently) and that is just about free and one gets the extra benefits.
The choice is yours as always.
(pretyped to save time)

Now I not saying that you should swap again just a suggestion should you want to.

Now I am assuming you have tied the WD test tool?? Software and Firmware Downloads | WD Support

Now I really don't know what to make of your system specs either so could you update them mate.
Now before we can help we do need to know what is in your machine so please do this System Info - See Your System Specs
or either enter the specs of your system in your forum profile the specs will appear when we click on that little box bottom left of the post screen it is for me the preferable option as it is easy. As you may appreciate it is very hard when you don’t know what one is working with for example a diesel or petrol engine.
*(pretyped to save time)

The reason I ask is that I'm considering a new high-spec desktop: i7-7700K at 4+ GHz, 16 GB RAM, 512 GB SSD, Windows 10. That would surely solve my problems for around $1500. But if $100 of RAM or $200 of SSD would boost the existing box? ...

Hmm now I wanted to know your current specs to see if anything there was maybe throttling the system down and me I use SSD's exclusively now and I was actually wondering if you were still using a spinner but....

I suppose you have checked out the processes in the task manager? it might give you some idea of what is taking up the RAM at least. I run Kasperksy which is suppose to be a bit of a hog but truly I find it doesn't slow down any of my machines and I have six which I use for various purposes. If it were me I would be checking in the registry too to see if there are any remnants of AVG and MBAM lurking there as I find using the removal tools for AV's in particular Norton never remove the entries entirely. I am not saying that is the cause of the slowdown more that it keeps the registry clear of that sort of crap.
The other thing I use and I don't know if you do is CCleaner for keeping the rubbish down on my machines plus SupreAntiSpyware (SAS) which not only find the occasional malware but also a lot of adware stuff that may clog up your system.

The new build looks good though I have to say at the rate that things are moving with the tech stuff ie the new Intel Optane gear building is more than ever not "future proof". In fact the new build I was considering has now blown out the budget for me and to be honest I don't like the way that Intel and Microsoft are in cahoots with the new gear insomuch that nothing is back compatible and one is forced to use Windows 10 like it or not.
Having said that I do have two machines running 10 and I configure both to look like 7 (have attached a pic of the Start screen) as I am not a fan of the "app look" at all. It is faster of course and once the settings have been figured out and set as one likes I find it as usable as 7 - just that I like 7 a tad more than 10. Oh plus I am making this travel laptop a dual 7/10 boot when I get home from hospital which I am really looking forward to after three months here

I reckon it might be worth you signing up for the sister forum at the top of this page - same crew and ask re your new build. Keep in mind that that Kabylake stuff is going to or could set you back a few more dollars than the older stuff was

Oh by the by I also wear Sketchers - size 8 LOL!!