Why is it taking so long to install Big Sur?

macOS Big Sur is Apple’s latest operating system for Mac computers, released in November 2020. It features a major redesign with a more modern look, new features like customizable icons, and better integration with iOS. While many users are excited about the update, there have been numerous complaints about excessively slow installation times. Some report waiting multiple hours for Big Sur to fully download and install on their machines.

In this article, we’ll investigate the potential reasons for these lengthy installs. What’s causing a process that once took under an hour to now require several? By examining factors like file size, system requirements, installation processes, and server loads, we can understand the issues at play and hopefully identify solutions to speed up upgrades.

File Size

macOS Big Sur represents a major evolution in terms of features and design from previous generations and this impacts the size of the installer and system requirements. The macOS Big Sur installer file is around 12GB, making it by far the largest macOS installer to date. This significant jump in size is roughly double the size of some previous macOS installers, like macOS High Sierra which was around 5GB (source). The large size of Big Sur is related to major architectural changes under the hood to allow for faster updates and new features moving forward.

After installation, macOS Big Sur takes up approximately 15GB of storage space. In comparison, previous versions like macOS Mojave took up 8-10GB. Overall, the increased size of Big Sur is a necessary tradeoff for the modern foundations that will power future innovation.

System Requirements

According to Apple’s macOS Big Sur technical specifications, Big Sur has some minimum system requirements that must be met to install and run the operating system properly. Big Sur requires a Mac running macOS 10.9 or later, at least 4GB of memory, and 35.5GB of available storage space on macOS Sierra or later versions. Some features like iCloud also require an Apple ID.

Many users have older Macs that just barely meet these system requirements, if at all. For machines running close to the minimum specs, the Big Sur upgrade process may take quite a long time as the system struggles to delete and replace system files while running low on storage and memory. Upgrading is also not recommended on systems that do not meet the minimum requirements.

Installation Process

The installation process for macOS Big Sur can be lengthy and encounter bottlenecks at certain steps. The basic process involves downloading the installer, preparing for installation by backing up the Mac, and then actually installing the OS update. Some of the key steps include:

Downloading the nearly 12GB Big Sur installer file from the App Store, which can take a long time depending on internet speeds (Source). The large file size makes the download slow.

Creating a bootable USB installer drive, which involves formatting the drive, downloading the installer again, and transferring the installer to the drive (Source). This also takes time.

The actual installation involves copying files, configuring settings, optimizing the storage, and more. The entire process can take over an hour on many machines as the OS updates system files and apps.

Overall, the installation process has multiple steps that require downloading large files, preparing drives, and systematically updating system files. Bottlenecks like slow internet or an older hard drive can substantially increase the install time.

User Files

One potential cause for the lengthy Big Sur installation time is that the installer needs to convert many of the user’s files to make them compatible with the new operating system (Apple). For example, the upgrade process may need to convert documents, media files, or even apps saved on the user’s system. Converting these files can take considerable time, especially for users who have large libraries of documents and media.

Some of the file types commonly affected include documents (.pages, .docx, .pdf), images (.jpg, .png), videos (.mov, .mp4), music (.mp3, .aac), and even certain apps and game save files. The sheer amount of user files that need conversion could significantly slow down the upgrade.

So in summary, Big Sur’s changes to the system and file architecture mean that existing user documents and media need to be converted before the OS can be fully installed. This conversion process happens in the background but can still slow things down substantially (Apple).

Installer Bug

Shortly after the initial release of macOS Big Sur, there were widespread rumors and reports of bugs in the Big Sur installer that caused installs to stall or fail for many users. The issues seemed particularly prevalent with the M1-based MacBook Pro and MacBook Air models that had just been released.

The installer problems manifested in different ways, from repeated reboots during install to becoming stuck in an endless loop. In some cases, the failed installs resulted in data loss as user files were deleted without the OS actually being upgraded. Understandably, this caused a great deal of frustration for eager upgraders.

Apple acknowledged the installer issues and quickly released a revised macOS 11.0.1 update that addressed the bugs. Users were encouraged to upgrade to the patched version of Big Sur once available to avoid any installation problems. While early OS releases often have bugs to iron out, the severity of the installer issues likely contributed to slower adoption rates of Big Sur in the first few weeks after launch.

Internet Speeds

Slow internet connection speeds can lead to long download times for large files like operating system updates. The average internet speed in the United States is around 200 Mbps according to Speed reports says US Has World’s 8th Fastest Internet. However, speeds can vary widely across the country, with some rural areas still stuck on older, slower broadband connections. Even with a relatively fast 200 Mbps connection, downloading a 12+ GB operating system update can take over an hour. For users with slower speeds, it may take multiple hours just to download Big Sur. This extended download time is one factor contributing to the overall lengthy install process.

Server Load

One key reason that the macOS Big Sur installation has been slow for many users is heavy server demand on release day. When a major operating system update like Big Sur is made available to the public, a huge surge of users try to download and install it immediately. This spike in traffic puts a strain on Apple’s update servers.

According to user reports on Reddit and Apple support forums, on launch day many people found the Big Sur download to be very slow, sometimes less than 1 Mbps. One Reddit thread described slow speeds even with a high-bandwidth connection. This indicates that heavy demand, rather than the user’s own connection, was responsible for the delays.

The rush of users all attempting to upgrade to Big Sur at the same time overwhelmed Apple’s servers, resulting in temporarily slowed download speeds. This highlights the need for patience from users, as it can take some time for servers to catch up to release day demand.

User Patience

When installing major operating system updates like macOS Big Sur, users should expect the process to take much longer than minor updates. However, many users perceive Big Sur as taking longer to install than previous macOS versions. This can lead to frustration and impatience.

According to MiniTool, upgrading from an older Windows version to Windows 10 can take hours or even all day due to updating Windows components during installation. Similarly, Big Sur may need to update and reconfigure many system files. Users upgrading from older macOS versions like Mojave or High Sierra should be prepared for a lengthy install time.

Although it may feel slower, Apple has not indicated Big Sur requires markedly longer install times than Catalina. However, user perception can make the process feel excessively long. Managing expectations around normal install times for major OS updates like Big Sur can help users stay patient.


In this article, we went over some of the main reasons why installing macOS Big Sur can end up taking a long time. The large file size of the installer, hardware requirements, and the complex installation process all contribute to a lengthy upgrade. Users with large personal files and folders can also prolong the process, as these need to be transferred over to the new OS.

To help speed things up, make sure your internet connection is fast and stable during installation. If possible, plug into ethernet instead of using WiFi. Also try freeing up extra disk space by offloading files to external drives beforehand. Avoid starting the install if you’re low on time or patience. And if you run into installer bugs, workarounds like restarting, trying again, or even clean installing may help.

Installing major OS updates is never a quick or painless process. But with the right preparation and setup, you can minimize headache and disruption. Remember to be patient, backup critical data, and set aside ample time to upgrade to Big Sur.