I've been there. I used to think it was just Windows being Windows—inevitable slowdown, time to reinstall or buy a new machine. But after years of digging, tweaking, and pulling my hair out, I found the culprit. It's not just "Windows getting old." There's a specific feature, something that's actually designed to help you, that's secretly eating your RAM alive and slowing everything down over time.
I'm talking about a feature with a few different names depending on your Windows version: SysMain, SuperFetch, or Prefetch. These are all part of a system Microsoft calls Delivery Optimization—and yes, it's probably running on your PC right now without you ever knowing it existed.
What Is Delivery Optimization and Why Does Windows Use It?
First, let's understand what we're dealing with. Delivery Optimization is a feature Microsoft introduced to make updating Windows and downloading apps from the Microsoft Store faster and more reliable. It's like BitTorrent, but built into Windows.
Here's how it's supposed to work. When you download a Windows update, instead of getting it all from Microsoft's servers (which can be slow and expensive for Microsoft), Delivery Optimization lets your PC grab pieces of that update from other computers on your local network or even from PCs on the internet. It's peer-to-peer sharing, Microsoft-style.
The theory is simple. More sources means faster downloads and less strain on Microsoft's servers. For businesses with many PCs on the same network, it can save huge amounts of bandwidth. Instead of 100 computers each downloading the same 1GB update from the internet, they grab it from each other locally. Genius, right?
But here's where it gets problematic. To make this work, Windows runs background services that track what updates are available, what pieces your PC has, and what pieces it needs to share with others. These services—Delivery Optimization, SysMain (formerly SuperFetch), and Prefetch—run constantly. They use RAM, CPU, and disk activity even when you're not actively downloading anything.
On a powerful machine with plenty of resources, this is barely noticeable. But on older hardware, budget laptops, or systems with limited RAM, these services can slowly choke your performance over time. They accumulate data, hold onto memory, and never fully let go.
If you've ever opened Task Manager, looked at your RAM usage, and thought "why is 80% of my memory used when I only have three tabs open?"—Delivery Optimization and its related services might be your answer.
The Three Culprits – SysMain, SuperFetch, and Prefetch
Let's break down exactly what each of these related features does, because Microsoft loves renaming things and it gets confusing.
SysMain / SuperFetch (Same Thing, Different Names)
This is the main memory eater. SuperFetch was the original name in Windows Vista through early Windows 10. Around Windows 10 version 1809, Microsoft renamed it to SysMain in the services list, but it's the exact same technology.
What it does: Watches which applications you use most often. Chrome in the morning, Excel in the afternoon, games at night. It learns your patterns. Then it pre-loads parts of those frequently-used applications into your RAM before you even click them. The idea is faster app launches. The reality is it holds onto memory aggressively and doesn't always let go when you need it.
On systems with limited RAM (4GB to 8GB), this is a disaster. Your limited memory fills up with cached data, leaving nothing for actual work. Your system starts using the page file (hard drive pretending to be RAM), and suddenly everything slows to a crawl.
Prefetch
Prefetch is related but slightly different. It's been around since Windows XP. Prefetch monitors which files are loaded when you start certain applications and during boot. It creates a "map" of these files and stores them in a more organized way on your hard drive so they can be accessed faster.
The problem: Prefetch creates and maintains files in C:\Windows\Prefetch. Over months and years, this folder can accumulate thousands of entries. Windows constantly reads and writes to these files, causing disk activity. On SSDs this is less noticeable, but on old HDDs it can contribute to that feeling of "my computer is always doing something."
Delivery Optimization Itself
The actual Delivery Optimization service (cryptically named "DoSvc" in the services list) handles the peer-to-peer update sharing. It runs in the background, checking for update pieces to share, maintaining connections, and using memory even when you're not actively downloading.
If you're on a metered connection, or if you just don't want your PC acting as a server for other people's updates, this service is unnecessary. Yet it runs by default on most Windows installations.
These three services work together under the Delivery Optimization umbrella. And together, they can quietly consume resources until your once-fast PC feels like it's running through mud.
How These Features Can Become a Problem
Okay, so why do well-intentioned features go bad? There's a few reasons.
They Don't Always Let Go of Memory
SysMain and SuperFetch are designed to use unused RAM. The thinking is: unused RAM is wasted RAM. So it fills that unused space with cached data. That's fine when you have plenty of free memory. But when you actually need that RAM for a new application, it's supposed to release it immediately. In practice, sometimes it's slow to let go. Sometimes it holds on longer than it should. And when you're trying to run a memory-hungry program like a game or video editor, that delay causes stuttering, lag, and slowdowns.
They're Overkill on Modern SSDs
SuperFetch and Prefetch were designed back when most computers used slow mechanical hard drives. Pre-loading data into RAM made a huge difference when hard drives took seconds to find files. But on modern SSDs, where access times are measured in microseconds, the benefit is tiny. Yet the services still run, still use RAM, still create disk activity—for almost no real-world gain.
They Can Run Wild on Systems with Limited RAM
If you have 16GB or 32GB of RAM, these services might not bother you much. But if you're on a budget laptop with 4GB or 8GB—which is still super common—they can be a real problem. They fill your limited memory, leaving little for actual work. Your system starts using the page file, and suddenly your computer feels like it's moving through molasses.
They Can Leak Memory Over Time
This is the sneaky one. Memory leaks happen when a program allocates memory but never fully releases it. Over days of uptime, these small leaks add up. Eventually, you're left with a system that's sluggish, unresponsive, and desperately needs a reboot. And SysMain, in particular, has been known to have these kinds of leaks—especially on older Windows builds.
They Cause High Disk Usage on Some Systems
If you're still using an old-school hard drive, Prefetch and SysMain can sometimes go haywire, causing constant disk activity at 100%. Your system slows to a crawl, and opening anything takes forever. This was a huge complaint in early Windows 10 days—people checking Task Manager and seeing "System" or "SysMain" using 100% disk. If that's ever happened to you, yeah, this is why.
The frustrating part is that these services run silently. There's no pop-up, no notification. They just do their thing in the background, slowly degrading your performance until one day you're wondering why your "fast" computer feels like a dinosaur.
How to Check If These Services Are Causing Your Problems
Before you go disabling things left and right, let's figure out if Delivery Optimization and its friends are actually the problem on YOUR machine. Here's how to check.
Step 1: Open Task Manager
Press Ctrl + Shift + Esc on your keyboard. That's the shortcut to jump straight to Task Manager. If you're on Windows 11, it opens to a simplified view—click "More details" at the bottom to see the full picture.
Step 2: Check Memory Usage
Look at the "Memory" column. Sort by it (click the column header) to see what's using the most RAM. Do you see something called "Service Host: SysMain" or just "SysMain" near the top? Also look for "Delivery Optimization" or "DoSvc." If any of these are using hundreds of MB or even a GB of RAM, that's suspicious.
Step 3: Check Disk Usage
Still in the Processes tab, look at the "Disk" column. Is anything related to SysMain or Delivery Optimization showing high disk activity? Also check the "Performance" tab, then select "Disk 0" (or your main drive). Look at "Active time." If it's consistently high—like 90 to 100%—when you're not doing anything intensive, these services could be the cause.
Step 4: Check the Prefetch Folder
Open File Explorer and go to C:\Windows\Prefetch. Windows might ask for permission—click Continue. Look at how many files are in there. Hundreds? Thousands? Each file represents an application that's been tracked. A large Prefetch folder means Windows is constantly tracking and optimizing, which uses resources. You can also check the folder size—if it's hundreds of MB, that's another clue.
Step 5: Check Delivery Optimization Settings
Go to Settings > Update & Security > Delivery Optimization (or just search "Delivery Optimization" in Start). Click "Advanced options." Look at the settings for "Download settings" and "Upload settings." If it's set to allow downloads from PCs on the internet, your machine could be acting as a server for strangers' updates, using bandwidth and resources.
Step 6: Check Your System Uptime
Still in Task Manager, go to the "Performance" tab and look at the "Up time" at the bottom. If your system has been running for days or weeks without a reboot, memory leaks have had time to build up. This is when problems often become noticeable.
If you're seeing high resource usage from these services, combined with general system sluggishness, there's a good chance disabling them will help.
How to Disable Delivery Optimization and Related Services
Alright, let's get to the fix. Disabling these services is safe and can be reversed. If you notice problems afterward, you can always turn them back on. Here's how to do it.
First: Disable Delivery Optimization Itself (The Easy Part)
1. Open Settings (Windows Key + I).
2. Go to Update & Security > Delivery Optimization (on Windows 10) or Windows Update > Advanced options > Delivery Optimization (on Windows 11).
3. Turn off the toggle for "Allow downloads from other PCs."
4. Click "Advanced options" and make sure both download and upload settings are set to "Off" or the most restrictive options.
This stops your PC from sharing updates with the internet or your local network. It doesn't fully disable the service, but it stops the worst resource usage.
Second: Disable SysMain via Services (Most Important)
1. Press Windows Key + R, type services.msc, and hit Enter.
2. Scroll down until you find SysMain. (If you're on an older Windows version, it might be called SuperFetch.)
3. Right-click on it and select Properties.
4. In the "Startup type" dropdown, change it from "Automatic" to Disabled.
5. If the service is currently running (it probably is), click the Stop button.
6. Click Apply, then OK.
This is the single most impactful change for freeing up RAM.
Third: Clear the Prefetch Folder (Easy and Safe)
1. Open File Explorer and go to C:\Windows\Prefetch.
2. Select all files (Ctrl + A) and delete them. Windows might keep a few files that are in use—that's fine, just delete the rest.
3. Empty your Recycle Bin to free up the space.
This won't disable Prefetch permanently, but it clears out the accumulated data. Windows will rebuild the folder, but starting fresh can help performance.
Fourth: Disable the Delivery Optimization Service Completely (Optional)
For full disabling, you can also stop the underlying service:
1. Open Services (services.msc) again.
2. Find Delivery Optimization (listed as "Delivery Optimization" or "DoSvc").
3. Right-click, Properties, set Startup type to Disabled, and click Stop.
4. Click Apply and OK.
Note: This might affect Windows Update speed slightly, as you'll only download from Microsoft's servers. For most people on broadband, the difference is unnoticeable.
After doing any of these methods, restart your computer to make sure everything takes effect. Then give your system a day or two of normal use. You should notice:
- Lower RAM usage at idle (check Task Manager)
- Less constant disk activity
- Programs opening just as fast (or faster) without the overhead
- Overall smoother experience, especially if you had limited RAM
What If Disabling These Doesn't Help?
Okay, you disabled Delivery Optimization, SysMain, and cleared Prefetch, but your computer's still slow. What now? These are common problems, but they're not the only ones. Here's what else to check.
Check Other Startup Programs
Open Task Manager, go to the "Startup apps" tab. Disable anything you don't need opening automatically. That gaming launcher, that Adobe updater, that random printer software—they all eat RAM and CPU in the background. Every program you disable frees up resources.
Check for Malware
Run a full scan with Windows Defender or your antivirus of choice. Malware can hijack your system and use resources without you knowing. It's always worth ruling out. Consider using Malwarebytes for a second opinion—the free version is great for occasional scans.
Check Your Browser
Modern browsers are RAM hogs. Open Task Manager while Chrome or Edge is running. Look at the sub-processes. Too many extensions? Too many tabs? Close what you don't need. Consider using a more lightweight browser if you're on limited RAM. Also check for browser extensions you don't actually use—they run in the background constantly.
Check for Driver Issues
Outdated or corrupted drivers can cause all sorts of performance problems. Go to Device Manager (right-click Start), look for any devices with yellow exclamation marks. Update your graphics driver, chipset driver, and storage controller driver from the manufacturer's website—not just through Windows Update. For many users, outdated graphics drivers cause mysterious slowdowns.
Check Your Hard Drive Health
If you're still on an old mechanical hard drive, that might be your real problem. Consider upgrading to an SSD. It's the single biggest performance upgrade you can make for an older computer. HDDs are just slow, and no amount of software tweaking will change that. A 240GB SSD can be had for under $30 and will transform your machine.
Check for Windows Bloatware
Windows 10 and 11 come with a lot of pre-installed apps you probably don't need. Xbox stuff, News, Weather, Skype, Candy Crush (yes, really). You can uninstall many of them through Settings > Apps > Installed apps. Every little bit helps, especially on low-end hardware.
Add More RAM
If your system only has 4GB or 8GB, and you regularly run multiple programs, you might simply need more memory. RAM is relatively cheap, and it's often the bottleneck on older machines. Check if your laptop or desktop allows upgrades. For many older machines, going from 4GB to 8GB or 8GB to 16GB makes a massive difference.
Check Power Settings
If you're on a laptop, check your power plan. "Power Saver" mode dramatically reduces performance. Switch to "Balanced" or "High Performance" to see if it helps. In Control Panel > Power Options, you can also adjust advanced settings to prevent the CPU from slowing down unnecessarily.
Why Microsoft Keeps These Features On By Default
You might be wondering: if these features cause problems for some people, why does Microsoft keep them enabled? It's a fair question.
The answer is that for most users, on modern hardware, these features actually do what they're supposed to. They improve performance more often than they hurt it. On a system with plenty of RAM, a fast SSD, and a decent CPU, the benefits outweigh the costs.
Delivery Optimization genuinely speeds up updates for many people, especially in offices with multiple PCs. SysMain really does make frequently-used apps open faster on mechanical hard drives. Prefetch helps boot times and application load times on older hardware.
The problems arise on specific setups:
- Systems with limited RAM (4GB to 8GB)
- Systems with slow hard drives where the overhead becomes noticeable
- Systems that rarely reboot (letting memory leaks build up)
- Certain Windows versions with bugs (like early Windows 10 builds)
- Budget laptops where every megabyte of RAM counts
Microsoft's data probably shows that these features help more people than they hurt. So they leave them on by default. It's the classic trade-off: make things work well for the average user, and let the edge cases tweak things manually.
That's where you come in. If you're in one of those edge cases, now you know how to fix it.
Should You Keep Them Disabled Forever?
Once you disable these features, you might wonder if you should ever turn them back on. Here's my take.
Keep them disabled if:
- You're on a system with 8GB RAM or less (definitely keep SysMain off)
- You have an old HDD and disabling helped with disk usage
- You noticed a real improvement after disabling them
- You prefer maximum free RAM over potentially faster app loading
- You're on a metered internet connection and don't want update sharing
Consider turning them back on if:
- You upgrade your RAM (to 16GB or more)
- You switch to a fast SSD and want to experiment
- You notice that frequently-used apps feel slower to open without SysMain
- You're on a modern system and want to give them another try
- You work in an office with many PCs and want faster local updates
The nice thing is that it's easy to switch back. If you turn something back on and notice problems again, just disable it. You're in control.
For most people reading this article—especially if you found it because your computer feels slow—I'd recommend keeping Delivery Optimization's sharing disabled and SysMain disabled permanently. The resource savings are worth more than the small speed benefits on modern hardware.
Conclusion
Windows is complicated. There are thousands of moving parts, and sometimes well-meaning features cause unexpected problems. Delivery Optimization, SysMain, SuperFetch, and Prefetch are examples of that. They're supposed to help, and for many people they do. But for a significant number of users—especially those with older hardware or limited RAM—they become hidden performance killers.
The good news is that it's easy to check and easy to fix. Ten minutes in the Services panel and Settings could breathe new life into your sluggish computer. No reinstalling Windows, no buying new hardware (unless you want to). Just a few simple tweaks that might make everything feel faster again.
I've done this on my own machines, on family members' laptops, on friends' gaming rigs. More often than not, it helps. Not always dramatically, but enough to notice. Enough to stop the spinning wheel frustration. Enough to make an old laptop usable again.
So go ahead. Check your Task Manager. Look at your RAM usage. See if Delivery Optimization or SysMain are hogging resources. Try disabling them. Your computer might just thank you.
And if nothing else, you've learned a little more about how Windows works under the hood. Knowledge is power—especially when it comes to keeping your PC running smoothly.
FAQs:
1. Is it safe to disable Delivery Optimization and SysMain?
Yes, absolutely. These are performance features, not critical system parts. Disabling them will not break Windows or cause stability problems. You can always turn them back on if you change your mind.
2. Will disabling SysMain make my apps open slower?
Maybe, but probably not much on modern hardware. The feature is meant to pre-load apps, but on SSDs, the speed difference is tiny. Many users find their system feels quicker overall because more RAM is available for things they're actually using.
3. What's the difference between SysMain and SuperFetch?
Same thing, different name. Earlier Windows versions called it SuperFetch. Around Windows 10 version 1809, Microsoft renamed it to SysMain in the services list. They're the same technology.
4. How much RAM should these services be using normally?
There's no set number. But if SysMain is using 500MB or more on a system with limited RAM, that's a problem. If it's using over 1GB on any system, that's too much. Delivery Optimization should use very little when not actively downloading.
5. Do these features affect gaming performance?
They can. Games need memory. If SysMain is holding onto RAM, games might stutter, load slower, or run poorly—especially if your system starts using the page file. Many gamers disable SysMain and Delivery Optimization for this reason.
6. Will this work on Windows 10 and Windows 11?
Yes. These features exist on both, and the steps to disable them are almost the same. I've tested it on both versions.
7. Do I need to disable these if I have an SSD?
Not necessarily. SuperFetch was made for HDDs. On SSDs, the speed benefit is smaller, but SysMain can still cause memory issues. If you have plenty of RAM (16GB or more), you might not notice. If you have limited RAM, disabling it can still help no matter what drive you have.
8. What other Windows services can I safely turn off to improve performance?
Be careful here. Turning off the wrong service can cause problems. Besides SysMain and Delivery Optimization, services like "Windows Search" (if you don't use search often) and "Print Spooler" (if you don't have a printer) are sometimes turned off by advanced users. But look into each one before touching it. When in doubt, leave it alone.
9. Will disabling these improve battery life on my laptop?
Possibly. If these services were causing high disk or CPU activity, turning them off could reduce power use. But the effect is usually small. The main benefit is performance and available RAM, not battery.
10. I turned everything off and nothing changed. What now?
Then these weren't your main problem. Check the other areas I mentioned: startup programs, malware, browser usage, hard drive health, and RAM size. Your slowdown might have a different cause—maybe a failing hard drive, overheating CPU, or simply not enough RAM for what you're trying to do.