Using compact flash as a hard drive

Old IDE hard drives are slow and unreliable, due to their age. What if I could tell you there’s a cheap, readily available substitute that’s both solid state and faster? There is. Let’s talk about using compact flash as a hard drive.

Compact flash, as in digital cameras

Compact flash as IDE hard drive
Inexpensive adapters like this one let you substitute a compact flash card for an IDE hard drive. This card plugs straight into the IDE connector and uses a floppy drive power connector.

Compact flash cards communicate using the same standards as IDE hard drives. So adapters to turn them into hard drive workalikes are very simple and cheap. These make using compact flash as a hard drive very affordable and practical.

A compact flash card won’t keep pace with a modern SSD in terms of transfer rate or random I/O. But for retro computing, it doesn’t need to. MS-DOS is a single tasking operating system, and on Pentiums, IDE generally tops out at 33 or 66 megabytes per second at best. On 386 and 486 systems, it tops out at a fraction of that. So a compact flash card offers a better transfer rate than vintage hard drives and much better seek times. They are faster, quieter, run cooler, use less power, and are more reliable. What’s not to like?

Selecting a compact flash card

Remember, most vintage systems had very limited capacity drives. DOS itself has a limit of 8.5 GB, so there is no reason to use a drive larger than 8 GB. So depending on the vintage, even a half gigabyte may be bigger than some systems can handle. You may have to load an overlay to use a drive of even 512 megabytes.

Generally speaking, systems from before 1997 have a limit of 4.2 GB. Pre-1996 systems often have a limit of 2.1 GB. And pre-1996 systems that can’t take a 2 GB drive often can only take a 504 MB drive.

Old MS-DOS versions, such as the ubiquitous DOS 6.22, are limited to disk partitions of 2 GB in size. So if you use a card larger than 2 GB, you’ll have to use multiple partitions.

Given these limitations, it makes sense to select an 8 GB card for late 1990s systems such as late Pentium II systems. Pentiums take better to 2 or 4 GB cards. Late 486 systems take well to 2 GB cards. Early 486 systems and 386 systems are happiest with 512 MB cards.

Connecting the adapter

Here is a compact flash-IDE adapter in use, plugged into an IDE socket on a motherboard.

Many adapters just plug straight into the 40-pin IDE connector. The compact flash card plugs into a slot on the adapter. For power, use a 3.5″ floppy drive power connector. And that’s it. The whole setup takes very little space and saves you some cable-routing pain.

Other adapters have a 40-pin socket on them to take an IDE cable like a hard drive does. These setups are better for systems that don’t have a lot of vertical clearance near the IDE connectors, or if you want to connect two drives to a particular IDE connector.

The very nicest adapters bolt onto an ISA bracket inside the machine and allow you to remove the card without opening the machine. These are convenient because you can take the card out of the machine and plug it into a newer PC to copy data onto it easily.

If you don’t have enough 3.5″ floppy power connectors, use a Molex to mini 4-pin power cable adapter┬áto convert the power connector intended for the hard drive into one suitable for the compact flash adapter.

Using compact flash as a hard drive

Once you install MS-DOS on a compact flash drive standing in for a hard drive, you’ll find it’s very fast. DOS itself boots in seconds, and most programs load in seconds. Random writes tend to be a bit slow, but tasks like retro gaming tend not to do a lot of random writes, so you may never notice the limitations of the compact flash in a vintage system.

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