Types and Uses of Drive Bays in PC Cases [Custom PC Guide]

The drive bays in a PC case are mainly spaces for installing storage devices, and the type and number of drive bays needed will change depending on the storage configuration.

If a PC case is chosen without the right type or number of drive bays, it may not be possible to install the desired storage devices.

This article explains the role and types of drive bays in PC cases, as well as how to read the specifications for drive bays in PC cases.

Key Points of This Article

Drive bays are mainly spaces for installing storage devices
There are four types of drive bays, each with a specific use
Check the drive bay specifications according to the type and number of storage devices to be installed
Shadow bays (internal bays) are for storage devices that do not need to be accessed from outside
The 5.25-inch bay for optical drives and expansion parts can be accessed from outside
Recently, many builds use NVMe SSDs, so drive bays are sometimes not used
Drive bay specifications may include terms like “2.5/3.5 shared” or “+1”, so be careful

This article also explains how to choose a PC case from the perspective of basic knowledge such as manufacturer and size, as well as performance and compatibility.

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Basics of PC Case Drive Bays

This section explains the basics of drive bays in PC cases.

Basics of PC Case Drive Bays

What is a Drive Bay?
The Four Types of Drive Bays and Their Uses
What is a Shadow Bay?

What is a Drive Bay?

A drive bay is a space inside a PC case used for installing storage devices and other expansion parts.

Specifically, it refers to the physical space for securing SATA SSDs, HDDs, optical drives, card readers, and so on.

*In this article, SATA SSD is written to distinguish it from NVMe SSDs.

Since drive bays are mainly for installing storage devices, it is necessary to choose a PC case with the right type and number of drive bays according to the storage configuration.

The Four Types of Drive Bays and Their Uses

There are four types of drive bays in PC cases, and each has a specific use for what can be installed.

Type of Drive Bay	Use
2.5-inch drive bay	SATA SSD
3.5-inch drive bay	HDD
2.5/3.5 shared inch drive bay	SATA SSD, HDD
5.25-inch drive bay	Optical drives, expansion parts such as card readers and USB ports

As shown above, each type of drive bay has a specific use, so it is necessary to choose a PC case according to the storage configuration being considered.

Some PC cases have only 2.5-inch drive bays, while others have no 5.25-inch drive bays. If a PC case is chosen based only on design or price, it may not be possible to install the desired devices, so be careful.

Recently, about 80% of storage configurations use only NVMe SSDs, so drive bays are used less often.

Therefore, depending on the storage configuration, it may not be necessary to worry about drive bays, but if SATA SSDs, HDDs, optical drives, or multiple storage devices are to be used, be sure to check the specifications.

What is a Shadow Bay?

A shadow bay is a type of drive bay installed inside a PC case that is located where it cannot be accessed directly from outside.

For example, it may be written as follows:

・Internal 3.5-inch ×2, Internal 2.5-inch ×2, External 5.25-inch ×2

Details on how to read drive bay specifications will be explained later.

Besides “shadow bay,” the term “internal” may also be used, and in contrast, “external” is used for bays accessible from outside.

External bays are for drives that can be accessed from outside the case, while internal (shadow) bays are for drives that stay inside the case.

Basically, 2.5-inch and 3.5-inch drive bays are usually “internal (shadow)”, and 5.25-inch drive bays are “external”.

For example, when installing storage in 2.5-inch or 3.5-inch drive bays, there is usually no need to access them from outside during normal PC use, except for upgrades or replacements.

Therefore, these drive bays are located completely inside the PC case.

On the other hand, “external (shadow)” bays are for installing expansion parts such as optical drives, USB ports, and card readers. The DVD slot, USB ports, and SD card slots need to be accessible to the user.

Therefore, the 5.25-inch drive bay is designed so that the slot appears on the front of the PC case.

Types of PC Case Drive Bays

This section explains the types of drive bays in PC cases.

Types of PC Case Drive Bays

3.5-inch Drive Bay (HDD)
2.5-inch Drive Bay (SATA SSD)
5.25-inch Drive Bay (Optical Drive)
2.5/3.5 Shared Inch Drive Bay (SATA SSD / HDD)

Generally, there are these four types, so it is important to check how many of each type are available and choose a PC case based on the storage configuration and future expandability.

3.5-inch Drive Bay (HDD)

The 3.5-inch drive bay is mainly for installing HDDs.

Some small PC cases, and occasionally even standard PC cases, may not have a 3.5-inch drive bay, so caution is needed.

Recently, fewer users install HDDs, but if an HDD is to be installed, make sure the case has a 3.5-inch drive bay.

Ken

In the past, floppy disk drives were also installed in these!

2.5-inch Drive Bay (SATA SSD)

The 2.5-inch drive bay is mainly for installing SATA SSDs.

Recently, NVMe SSDs installed in the motherboard’s M.2 slot are often used, so 2.5-inch drive bays are less common. However, if a second or more SATA SSD is to be installed as sub-storage, or if storage is to be added easily, the 2.5-inch drive bay is often used.

Ken

It can be difficult to add more NVMe SSDs later due to workspace or interference with other parts, but SATA SSDs are usually easier to add!

5.25-inch Drive Bay (Optical Drive)

The 5.25-inch drive bay is for installing optical drives and other expansion parts.

In the past, many PC cases came standard with 5.25-inch bays for CD/DVD/Blu-ray drives, but recently, the use and demand for optical media has decreased, so more cases do not include this bay.

Therefore, if a part that requires a 5.25-inch drive bay is needed, always check that the case has this bay.

Other expansion parts that can be installed in the 5.25-inch bay include:

Card reader
SSD / HDD mount
Expansion units for USB ports or audio jacks

For those who often use SD cards for photography or video, a card reader can make data transfer smoother.

Also, if a PC case is chosen for other reasons but there is no plan to use the 5.25-inch bay, it can be used as a storage drive bay.

In addition, if many USB devices are frequently connected and disconnected, adding more USB ports to the front panel can improve convenience.

By installing such expansion parts, more specific needs can be met.

2.5/3.5 Shared Inch Drive Bay (SATA SSD / HDD)

The 2.5/3.5 shared inch drive bay is a flexible bay that can hold both 2.5-inch and 3.5-inch drives.

In other words, it supports both SATA SSDs and HDDs, and either a SATA SSD or an HDD can be installed in one drive bay.

If the drive bay specification includes words like “2.5/3.5”, “shared”, “combo”, or “共用”, it means both types are supported.

This shared type of drive bay is compatible with both, so it saves space and is highly versatile. Most recent PC cases use this type.

This allows users to have more options for storage and to combine different sizes of drives as needed.

How to Read Drive Bay Specifications

This section explains how to read the specifications for drive bays in PC cases.

How to Read Drive Bay Specifications

Basic Notation and How to Read
When There is a 2.5/3.5 Shared Drive Bay
When There is a “+1”
Other Special Cases

Some specifications can be confusing, so let’s look at examples to avoid mistakes.

Basic Notation and How to Read

Examples of basic drive bay specifications for PC cases are as follows:

・2.5-inch SSD ×5, 3.5-inch HDD ×2

・2.5-inch SSD ×4, 3.5-inch HDD ×4, 5.25-inch ×1

・Internal 3.5-inch ×2, Internal 2.5-inch ×2, External 5.25-inch ×2

Each line is the specification for one PC case, and several patterns are listed.

The details may differ depending on the PC case manufacturer or product, but basically, the number of 2.5-inch, 3.5-inch, and 5.25-inch drive bays is listed.

This is a very simple and easy-to-understand notation, so it should not be confusing.

When There is a 2.5/3.5 Shared Drive Bay

Examples of notation when there is a 2.5/3.5 shared drive bay are as follows:

・3.5/2.5-inch bay ×2, 2.5-inch bay ×1

・3.5/2.5-inch shared shadow bay ×2, 2.5-inch dedicated shadow bay ×3

・Internal 2.5/3.5-inch ×2, Internal 2.5-inch ×1

・5.25-inch ×1, 2.5-inch/3.5-inch (COMBO) ×2, 2.5-inch ×2

In the first example, there are two bays that can be used for either 2.5-inch or 3.5-inch drives, and one bay for 2.5-inch drives only.

This means the following storage configurations are possible:

Three SATA SSDs
Two SATA SSDs and one HDD
One SATA SSD and two HDDs

With shared drive bays, it is possible to support various storage configurations in a space-saving way compared to preparing separate bays.

If the specification includes words like “2.5/3.5”, “shared”, “combo”, or “コンボ”, it is a shared drive bay.

Also, as in the second example, if only one size is supported, it may be labeled as “dedicated” for clarity.

When the Number of 2.5/3.5 Shared Drive Bays Differs

・3.5-inch HDD ×1 or 2.5-inch SSD ×2

・3.5-inch HDD ×2 or 2.5-inch SSD ×4

・Internal 3.5-inch x 2 (compatible with 2.5-inch x 3)

In the previous examples, the number of 2.5-inch and 3.5-inch shared drive bays was the same.

However, as in these examples, the number of drives that can be installed may differ between 2.5-inch and 3.5-inch.

In the first example, one 3.5-inch drive or two 2.5-inch drives can be installed. In such cases, “or” is used, or “compatible” is written.

When There is a “+1”

Sometimes, a “+1” is written after the type and number of drive bays.

・3.5-inch bay ×2, 2.5-inch bay ×2+1

・3.5-inch drive bay ×1, 2.5-inch drive bay ×3+1 (converted from 3.5-inch drive bay)

The “+1” notation indicates an additional bay that can be used in addition to the standard bays.

This extra bay may require a different installation method or may only be available under certain conditions.

“+1” is mainly used in the following cases:

Unusual installation location
A drive can be installed in a different place, such as an empty space inside the case or behind the cable management area.
Example: Above the power supply unit, behind the cable routing space, etc.
Additional installation using an adapter or tray
An adapter can be used to add a different size drive to a standard bay.
Example: Using an adapter to install a 2.5-inch drive in a 3.5-inch bay, providing “+1” expandability.
Using an expansion bracket
The number of bays can be increased by using an extra bracket or optional part.
Example: An extra bracket installed on the side or top of the case.

For example, if it says “2.5-inch bay ×2+1“, it means there are two standard 2.5-inch drive bays, plus one more that can be used.

This “+1” usually means the extra installation space is shared with another space or can only be used under certain conditions, such as when other drives or expansion cards are not installed.

This way, the “+1” notation shows an optional installation location in addition to the standard number of bays.

When checking drive bays in a PC case, it is helpful to look at both the specifications and actual images to see where the drive bays are located.

With standard notation, it is usually clear from the images, but when there is a “+1”, it is often difficult to tell from the images alone where the extra drive can be installed.

Sometimes, the “+1” is used simply because the location is separate, or it may be shared with another space, so using the “+1” drive may make another location unavailable.

Conversely, using another location may make the “+1” unavailable, so if planning to use the “+1” for storage, it is wise to consider the risk that it may not be usable.

Other Special Cases

Sometimes, special conditions are written in parentheses.

・3.5-inch bay ×3 (maximum with SFX power supply), or ×2 (maximum with ATX power supply)

・2.5-inch ×2 (includes 3.5-inch/2.5-inch HDD bracket ×1)

・Internal 3.5-inch ×2 (if no water cooling is installed)

・External 5.25-inch ×2, internal 3.5/2.5-inch shared ×6, internal 2.5-inch ×2, (with storage layout: external 5.25-inch ×2, internal 3.5/2.5-inch shared ×8, internal 2.5-inch ×2)

For example, in the first line, there are three 3.5-inch bays with an SFX power supply, or two with an ATX power supply.

The number of storage devices that can be installed changes depending on the size of the power supply unit.

The third line means that two internal 3.5-inch bays can be used if an air-cooled CPU cooler is used.

In the fourth line, some PC cases allow the layout to be changed by attaching or removing brackets, and by adding a storage bracket, two more internal 3.5/2.5-inch shared bays can be added.

Since various conditions may be written, if planning to install multiple storage devices or the maximum number allowed by the specifications, it is recommended to check the official product page of the PC case.

Summary: Check the Required Bays and Choose a Suitable PC Case!

This article explained the basics, types, and notation of drive bays in PC cases.

Here are the key points again.

Key Points of This Article

Drive bays are mainly spaces for installing storage devices
There are four types of drive bays, each with a specific use
Check the drive bay specifications according to the type and number of storage devices to be installed
Shadow bays (internal bays) are for storage devices that do not need to be accessed from outside
The 5.25-inch bay for optical drives and expansion parts can be accessed from outside
Recently, many builds use NVMe SSDs, so drive bays are sometimes not used
Drive bay specifications may include terms like “2.5/3.5 shared” or “+1”, so be careful

Recently, many storage configurations use a single NVMe SSD installed in the M.2 slot on the motherboard, so many users do not use drive bays.

However, if a PC is to be used for purposes that require a lot of storage, be sure to decide on the storage configuration (types and number of SATA SSDs/HDDs) and check if the PC case has the necessary drive bays.

Also, if planning to add more storage in the future in case more capacity is needed, consider that as well.

This article also explains how to choose a PC case from the perspective of basic knowledge such as manufacturer and size, as well as performance and compatibility.